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{{Short description|Limbless, scaly, elongate reptile}}
{{pp|small=yes}}
{{About|the reptile||Snake (disambiguation)}}
{{Improve|reason=uncited text, undue weight and bad structure|date=June 2024}}
{{use dmy dates|date=February 2021}}
{{Automatic taxobox
| fossil_range = <br/>[[Late Cretaceous]] - [[Holocene|Present]],<ref name=snake_origin_ecology/> {{Fossil range|94|0|earliest=112|latest=|PS=}}
| image = Trimeresurus sabahi fucatus, Banded pit viper - Takua Pa District, Phang-nga Province (46710893582).jpg
| image_caption = ''[[Trimeresurus sabahi]]''
| display_parents = 2
| taxon = Serpentes
| authority = [[Carl Linnaeus|Linnaeus]], [[10th edition of Systema Naturae|1758]]
| range_map = World distribution of snakes.svg
| range_map_caption = <small>Approximate world distribution of snakes, all species</small>
| subdivision_ranks = Infraorders
| subdivision = {{Linked taxon list
| Alethinophidia | Nopcsa, 1923
| Scolecophidia | [[Edward Drinker Cope|Cope]], 1864
}}
}}

'''Snakes''' are elongated [[Limbless vertebrate|limbless]] [[reptile]]s of the [[suborder]] '''Serpentes'''.<ref>{{cite journal |vauthors=Reeder TW, Townsend TM, Mulcahy DG, Noonan BP, Wood PL, Sites JW, Wiens JJ |title=Integrated analyses resolve conflicts over squamate reptile phylogeny and reveal unexpected placements for fossil taxa |journal=[[PLOS ONE]] |volume=10 |issue=3 |article-number=e0118199 |year=2015 |pmid=25803280 |pmc=4372529 |doi=10.1371/journal.pone.0118199 |bibcode=2015PLoSO..1018199R |doi-access=free|issn=1932-6203}}</ref> Cladistically [[Squamata|squamates]], snakes are [[ectothermic]], [[amniote]] [[vertebrate]]s covered in overlapping [[Scale (zoology)|scales]] much like other members of the group. Many species of snakes have skulls with several more joints than their [[lizard]] ancestors and relatives, enabling them to swallow prey much larger than their heads ([[cranial kinesis]]). To accommodate their narrow bodies, snakes' paired organs (such as kidneys) appear one in front of the other instead of side by side, and most only have one functional [[lung]]. Some species retain a [[pelvic girdle]] with a pair of [[vestigial]] claws on either side of the [[cloaca]]. Lizards have independently evolved elongate bodies without limbs or with greatly reduced limbs at least twenty-five times via [[convergent evolution]], leading to many lineages of [[legless lizard]]s.<ref>{{cite journal |vauthors=Wiens JJ, Brandley MC, Reeder TW |title=Why does a trait evolve multiple times within a clade? Repeated evolution of snakelike body form in squamate reptiles |journal=Evolution; International Journal of Organic Evolution |volume=60 |issue=1 |pages=123-41 |date=January 2006 |pmid=16568638 |doi=10.1554/05-328.1 |bibcode=2006Evolu..60..123W |s2cid=17688691 |url=http://doc.rero.ch/record/13623/files/PAL_E653.pdf |access-date=21 January 2023 |archive-date=2 February 2023 |archive-url=https://web.archive.org/web/20230202043249/http s://doc.rero.ch/record/13623/files/PAL_E653.pdf |url-status=live }}</ref> These resemble snakes, but several common groups of legless lizards have eyelids and external ears, which snakes lack, although this rule is not universal (see [[Amphisbaenia]], [[Dibamidae]], and [[Pygopodidae]]).

Living snakes are found on every continent except Antarctica, and on most smaller land masses; exceptions include some large islands, such as Ireland, Iceland, Greenland, and the islands of New Zealand, as well as many small islands of the Atlantic and central Pacific oceans.<ref name=Bauchot>{{cite book |editor-first=Roland |editor-last=Bauchot |title=Snakes: A Natural History |url=https://archive.org/details/snakesnaturalhis0000bauc/pa ge/220 |url-access=registration |year=1994 |publisher=Sterling Publishing Co., Inc. |location=New York |isbn=978-1-4027-3181-5 |page= 220}}</ref> Additionally, [[sea snake]]s are widespread throughout the Indian and Pacific oceans. Around thirty [[Family (biology)|families]] are currently recognized, comprising about 520 [[Genus|genera]] and about more than 4,170 [[species]].<ref name="NRDB-Cs">{{cite web |editor-last1=Uetz |editor-first1=Peter |editor-last2=Hallermann |editor-first2=Jakob |title=Search results for Higher taxa: snake |url=https://reptile-database.reptarium.cz/advanced_search?t axon=snake&submit=Search |access-date=7 February 2025 |website=The Reptile Database |publisher=Hamburg Museum of Zoology }}</ref> They range in size from the tiny, {{convert|10.4|cm|in|abbr=on|adj=mid|-long}} [[Barbados threadsnake]]<ref name="zootaxa"/> to the [[reticulated python]] of {{convert|6.95|m|ft|sp=us}} in length.<ref name="SunBear">{{cite journal |last=Fredriksson |first=G. M. |title=Predation on Sun Bears by Reticulated Python in East Kalimantan, Indonesian Borneo |journal=Raffles Bulletin of Zoology |volume=53 |issue=1 |year=2005 |pages=165-168 |url=http://dare.uva.nl/document/161117 |url-status=live |archive-url=https://web.archive.org/web/20140709001708/http ://dare.uva.nl/document/161117 |archive-date=July 9, 2014}}</ref> The fossil species ''[[Titanoboa|Titanoboa cerrejonensis]]'' was {{convert|12.8|m|ft|sp=us}} long.<ref name="head"/> Snakes are thought to have evolved from either burrowing or aquatic lizards, perhaps during the [[Jurassic]] period, with the earliest known fossils dating to between 143 and 167 [[Mega-annum|Ma]] ago.<ref>{{cite web |last=Perkins |first=Sid |name-list-style=vanc |date = 27 January 2015 |title=Fossils of oldest known snakes unearthed |url=https://www.science.org/content/article/fossils-oldest- known-snakes-unearthed |website=news.sciencemag.org |access-date=29 January 2015 |url-status=live |archive-url=https://web.archive.org/web/20150130043614/http ://news.sciencemag.org/paleontology/2015/01/fossils-oldest-k nown-snakes-unearthed |archive-date=30 January 2015}}</ref><ref>{{cite journal |vauthors=Caldwell MW, Nydam RL, Palci A, Apesteguia S |title=The oldest known snakes from the Middle Jurassic-Lower Cretaceous provide insights on snake evolution |journal=[[Nature Communications]] |volume=6 |article-number=5996 |date=January 2015 |pmid=25625704 |doi=10.1038/ncomms6996 |number=5996 |bibcode=2015NatCo...6.5996C |doi-access=free|hdl=11336/37995 |hdl-access=free }}</ref> The diversity of modern snakes appeared during the [[Paleocene]] epoch ({{circa}} 66 to 56 Ma ago, after the [[Cretaceous-Paleogene extinction event]]). The oldest preserved descriptions of snakes can be found in the [[Brooklyn Papyrus]].

Most species of snake are nonvenomous and [[Venomous snake|those that have venom]] use it primarily to kill and subdue prey rather than for self-defense. Some possess venom that is potent enough to cause painful injury or death to humans. Nonvenomous snakes either swallow prey alive or kill by [[constriction]].

== Etymology ==
The English word ''snake'' comes from [[Old English]] {{lang|ang|snaca}}, itself from [[Proto-Germanic]] {{lang|gem-x-proto|*snak-an-}} ([[cf.]] [[Germanic languages|Germanic]] {{lang|gem|Schnake}} 'ring snake', Swedish {{lang|sv|snok}} 'grass snake'), from [[Proto-Indo-European language|Proto-Indo-European]] root {{lang|ine-x-proto|*(s)neg-o-}} 'to crawl to creep', which also gave ''sneak'' as well as [[Sanskrit]] {{transliteration|sa|naga}} 'snake'.<ref>Proto-IE: {{lang|ine-x-proto|*(s)neg-o-}}, Meaning: snake, Old Indian: naga- m. 'snake', Germanic: {{lang|gem|*snek-a-}} m., {{lang|gem|*snak-an-}} m., {{lang|gem|*snak-o}} f.; {{lang|gem|*snak-a-}} vb., Russ. meaning: {{lang|ru|zhaba}} ({{lang|ru|zmeia}}), References: WP ({{lang|de|[[Indogermanisches etymologisches Worterbuch|Vergleichendes Worterbuch der indogermanischen Sprachen]]}}) II 697 f.</ref> The word ousted ''[[wikt:adder|adder]]'', as ''adder'' went on to narrow in meaning, though in Old English {{lang|ang|naeddre}} was the general word for snake.<ref>{{cite web |url=https://www.etymonline.com/word/snake |title=snake (n.) |website=etymonline.com |archive-url=https://web.archive.org/web/20100719112253/http ://www.etymonline.com/index.php?term=snake |archive-date=July 19, 2010 |url-status=live |access-date=September 22, 2009}}</ref> The other term, ''serpent'', is from French, ultimately from Indo-European {{lang|ine-x-proto|*serp-}} 'to creep',<ref name="serpent">{{cite web |work=Merriam-Webster Online Dictionary |title=Definition of serpent |url=http://www.merriam-webster.com/dictionary/serpent |access-date=12 October 2006 |url-status=live |archive-url=https://web.archive.org/web/20071017210917/http ://www.merriam-webster.com/dictionary/serpent |archive-date=October 17, 2007}}</ref> which also gave [[Ancient Greek]] {{lang|grc|erpo}} ({{transliteration|grc|herpo}}) 'I crawl' and Sanskrit {{transliteration|sa|sarpa}} 'snake'.<ref>{{cite book|url=https://books.google.com/books?id=M2aqp2n2mKkC&pg=P A193|title=Indo-European and the Indo-Europeans: A Reconstruction and Historical Analysis of a Proto-Language and Proto-Culture. |first1=Thomas V.|last1=Gamkrelidze|first2=Vjaceslav V.|last2=Ivanov|date=2010|isbn=978-3-11-081503-0|page=193|pu blisher=Walter de Gruyter }}</ref>

== Taxonomy ==

{{See also|List of snake genera}}
All modern snakes are grouped within the [[Class (biology)|suborder]] Serpentes in [[Linnean taxonomy]], part of the [[class (biology)|order]] [[Squamata]], though their precise placement within squamates remains controversial.<ref name="ITIS">{{ITIS|id=174118|taxon=Serpentes|access-date=4 April 2017}}</ref>

The two [[infraorder]]s of Serpentes are [[Alethinophidia]] and [[Scolecophidia]].<ref name="ITIS"/> This separation is based on [[comparative anatomy|morphological]] characteristics and [[mitochondrial DNA]] sequence similarity. Alethinophidia is sometimes split into [[Henophidia]] and [[Caenophidia]], with the latter consisting of "colubroid" snakes ([[colubrids]], [[Viperidae|vipers]], [[elapids]], [[Hydrophiinae|hydrophiids]], and [[Atractaspidinae|atractaspids]]) and acrochordids, while the other alethinophidian families comprise Henophidia.<ref name="Pou92">{{cite book |vauthors=Pough FH |orig-date=1992 |title=Herpetology: Third Edition |publisher=Pearson [[Prentice Hall]] |year=2002 |isbn=978-0-13-100849-6}}</ref> While not extant today, the [[Madtsoiidae]], a family of giant, primitive, python-like snakes, lived until 50,000 years ago in Australia, represented by genera such as ''[[Wonambi]]''.<ref name="Vasuki">{{Cite journal |last1=Datta |first1=Debajit |last2=Bajpai |first2=Sunil |date=2024-04-18 |title=Largest known madtsoiid snake from warm Eocene period of India suggests intercontinental Gondwana dispersal |journal=[[Scientific Reports]] |language=en |volume=14 |issue=1 |page=8054 |doi=10.1038/s41598-024-58377-0 |issn=2045-2322|doi-access=free |pmid=38637509 |bibcode=2024NatSR..14.8054D |pmc=11549349 }}</ref>

Recent molecular studies support the [[monophyly]] of the [[clades]] of modern snakes, scolecophidians, typhlopids + anomalepidids, alethinophidians, core alethinophidians, uropeltids (''Cylindrophis'', ''Anomochilus'', uropeltines), macrostomatans, booids, boids, pythonids and caenophidians.<ref name=Lee>{{cite journal |first1=Michael S. Y. |last1=Lee |first2=Andrew F. |last2=Hugall |first3=Robin |last3=Lawson |first4=John D. |last4=Scanlon |name-list-style=vanc |title=Phylogeny of snakes (Serpentes): combining morphological and molecular data in likelihood, Bayesian and parsimony analyses |journal=[[Systematics and Biodiversity]] |volume=5 |issue=4 |pages=371-389 |doi=10.1017/S1477200007002290 |year=2007 |bibcode=2007SyBio...5..371L |hdl=2440/44258 |s2cid=85912034 |hdl-access=free}}</ref>

=== Families ===
{|class="wikitable"
|-
| colspan="100%"|Infraorder '''[[Alethinophidia]]''' 25 families
|-
!|Family<ref name="NRDB-Cs"/>
!|Taxon author<ref name="NRDB-Cs"/>
!|Genera<ref name="NRDB-Cs"/>
!|Species<ref name="NRDB-Cs"/>
!|Common name
!|Geographic range<ref name="McD99">McDiarmid RW, Campbell JA, Toure T. 1999. Snake Species of the World: A Taxonomic and Geographic Reference, vol. 1. Herpetologists' League. 511 pp. {{ISBN|1-893777-00-6}} (series). {{ISBN|1-893777-01-4}} (volume).</ref>
|-
|[[Acrochordidae]]
|[[Charles Lucien Bonaparte|Bonaparte]], 1831
||1
||3
|Wart snakes
|style="width:40%"|Western India and Sri Lanka through tropical Southeast Asia to the Philippines, south through the Indonesian/Malaysian island group to Timor, east through New Guinea to the northern coast of Australia to [[Mussau Island]], the [[Bismarck Archipelago]] and [[Guadalcanal Island]] in the Solomon Islands.
|-
|[[Aniliidae]]
|[[Leonhard Hess Stejneger|Stejneger]], 1907
||1
||1
|False coral snake
|Tropical South America.
|-
|[[Anomochilidae]]
|Cundall, Wallach, 1993
||1
||3
|Dwarf pipe snakes
|West Malaysia and on the Indonesian island of [[Sumatra]].
|-
|[[Atractaspididae]]
|[[Albert Gunther|Gunther]], 1858
||12
||72
|Burrowing asps
|Africa and the Middle East
|-
|[[Boidae]]
|[[John Edward Gray|Gray]], 1825
||14
||61
|Boas
|Northern, Central and South America, the Caribbean, southeastern Europe and Asia Minor, Northern, Central and East Africa, Madagascar and [[Reunion Island]], the Arabian Peninsula, Central and southwestern Asia, India and Sri Lanka, the [[Maluku Islands|Moluccas]] and New Guinea through to Melanesia and Samoa.
|-
|[[Bolyeriidae]]
|[[Robert Hoffstetter|Hoffstetter]], 1946
||2
||2
|Splitjaw snakes
|[[Mauritius]].
|-
|[[Colubridae]]
|[[Nicolaus Michael Oppel|Oppel]], 1811
||258<ref name="NRDB-Cs"/>
||2055<ref name="NRDB-Cs"/>
|Typical snakes
|Widespread on all continents, except Antarctica.<ref name="Spa04">{{cite book |last1=Spawls |first1=S. |last2=Howell |first2=K. |last3=Drewes |first3=R. |last4=Ashe |first4=J. |date=2004 |title=A Field Guide To The Reptiles Of East Africa |location=London |publisher=A & C Black Publishers Ltd |isbn=0-7136-6817-2}}</ref>
|-
|[[Cyclocoridae]]
|[[Jeffrey L.Weinell|Weinell]] & [[Rafe M.Brown|Brown]], 2017
||5
||8
|Cyclocorids
|The Philippines
|-
|[[Cylindrophiidae]]
|[[Leopold Fitzinger|Fitzinger]], 1843
||1
||14
|Asian pipe snakes
|Sri Lanka east through Myanmar, Thailand, Cambodia, Vietnam and the Malay Archipelago to as far east as [[Aru Islands Regency|Aru Islands]] off the southwestern coast of New Guinea. Also found in southern China (Fujian, Hong Kong and on Hainan Island) and in Laos.
|-
|[[Elapidae]]
|[[Friedrich Boie|Boie]], 1827
||55
||389
|Elapids
|On land, worldwide in tropical and subtropical regions, except in Europe. Sea snakes occur in the Indian Ocean and the Pacific.<ref name="NRDB-E">{{NRDB family |page=elapidae.php |family=Elapidae |date=3 December |year=2008}}</ref>
|-
|[[Homalopsidae]]
|[[Charles Lucien Bonaparte|Bonaparte]], 1845
||28
||53
|Homalopsids
|Southeastern Asia and northern Australia.
|-
|[[Lamprophiidae]]
|[[Leopold Fitzinger|Fitzinger]], 1843
||16
||89
|Lamprophiids (formerly included Atracaspididae, Psammophiidae, and several other families)
|Africa (including the Seychelles)
|-
|[[Loxocemidae]]
|[[Edward Drinker Cope|Cope]], 1861
||1
||1
|Mexican burrowing snake
|Along the Pacific versant from Mexico south to Costa Rica.
|-
|[[Micrelapidae]]
|[[Sunandan Das|Das]] ''et al''., 2023
||1
||4
|Two-headed snakes
|Eastern Africa and the Levant
|-
|[[Pareidae]]
|Romer, 1956
||3
||20
|Snail-eating snakes
|Southeast Asia and islands on the Sunda Shelf (Sumatra, Borneo, Java, and their surrounding smaller islands).
|-
|[[Prosymnidae]]
|Kelly, Barker, Villet & Broadley, 2009
||1
||16
|Shovel-snout snakes
|Subsaharan Africa
|-
|[[Psammodynastidae]]
|Das ''et al''., 2024
||1
||2
|Mock vipers
|Tropical Asia
|-
|[[Psammophiidae]]
|[[Monique Bourgeois|Bourgeois]], 1968
||8
||55
|Psammophiids
|Africa (including Madagascar), Asia and southern Europe
|-
|[[Pseudaspididae]]
|[[Edward Drinker Cope|Cope]], 1893
||2
||2
| Pseudaspidids
|Subsaharan Africa
|-
|[[Pseudoxyrhophiidae]]
|[[Herndon G. Dowling|Dowling]], 1975
||22
||89
| Pseudoxyrhophiids
|Mostly Madagascar and the Comoros; 5 species in subsaharan Africa, 1 in Socotra
|-
|[[Pythonidae]]
|[[Leopold Fitzinger|Fitzinger]], 1826
||8
||40
|Pythons
|Subsaharan Africa, India, Myanmar, southern China, Southeast Asia and from the Philippines southeast through Indonesia to New Guinea and Australia.
|-
|[[Tropidophiidae]]
|[[L.D. Brongersma|Brongersma]], 1951
||2
||34
|Dwarf boas
|West Indies; also Panama and northwestern South America, as well as in northwestern and southeastern Brazil.
|-
|[[Uropeltidae]]
|[[Johannes Peter Muller|Muller]], 1832
||8
||55
|Shield-tailed snakes
|Southern India and Sri Lanka.
|-
|[[Viperidae]]
|[[Nicolaus Michael Oppel|Oppel]], 1811
||35
||341
|Vipers
|The Americas, Africa, and Eurasia east to [[Wallace Line|Wallace's Line]].
|-
|[[Xenodermidae]]
|[[Edward Drinker Cope|Cope]], 1900
||6
||18
|Dragon and odd-scaled snakes
|East Asia, Southern and southeastern Asia, and islands on the Sunda Shelf (Sumatra, Borneo, Java, and their surrounding smaller islands).
|-
|[[Xenopeltidae]]
|[[Charles Lucien Bonaparte|Bonaparte]], 1845
||1
||2
|Sunbeam snakes
|Southeast Asia from the [[Andaman Islands|Andaman]] and [[Nicobar Islands]], east through Myanmar to southern China, Thailand, Laos, Cambodia, Vietnam, the Malay Peninsula and the East Indies to [[Sulawesi]], as well as the Philippines.
|-
|[[Xenophidiidae]]
|Wallach & Gunther, 1998
||1
||2
|Spine-jawed snakes
|Borneo and peninsular Malaysia.
|}
<br />
{|class="wikitable"
|-
| colspan="100%"|Infraorder '''[[Scolecophidia]]''' 5 families
|-
!|Family<ref name="NRDB-Cs"/>
!|Taxon author<ref name="NRDB-Cs"/>
!|Genera<ref name="NRDB-Cs"/>
!|Species<ref name="NRDB-Cs"/>
!|Common name
!|Geographic range<ref name="McD99"/>
|-
|[[Anomalepidae]]
|[[Edward Harrison Taylor|Taylor]], 1939
||4
||18
|Primitive blind snakes
|style="width:40%"|From southern Central America to northwestern South America. Disjunct populations in northeastern and southeastern South America.
|-
|[[Gerrhopilidae]]
|style="width:15%"|Vidal, Wynn, Donnellan and Hedges 2010
||2
||18
|Indo-Malayan blindsnakes
|Southern and southeastern Asia, including Sri Lanka, the Philippines, and New Guinea.
|-
|[[Leptotyphlopidae]]
|[[Leonhard Hess Stejneger|Stejneger]], 1892
||13
||139
|Slender blind snakes
|Africa, western Asia from Turkey to northwestern India, on [[Socotra Island]], from the southwestern United States south through Mexico and Central to South America, though not in the high [[Andes]]. In Pacific South America they occur as far south as southern coastal Peru, and on the Atlantic side as far as Uruguay and Argentina. In the Caribbean they are found on the Bahamas, [[Hispaniola]] and the [[Lesser Antilles]].
|-
|[[Typhlopidae]]
|[[Blasius Merrem|Merrem]], 1820
||18
||266
|Typical blind snakes
|Most tropical and many subtropical regions around the world, particularly in Africa, Madagascar, Asia, islands in the Pacific, tropical America and in southeastern Europe.
|-
|[[Xenotyphlopidae]]
|Vidal, Vences, Branch and Hedges 2010
||1
||1
|Round-nosed blindsnake
|Northern Madagascar.
|}

=== Legless lizards ===
{{Main|Legless lizard}}
While snakes are limbless reptiles, evolved from (and grouped with) lizards, there are many other species of lizards that have lost their limbs independently but which superficially look similar to snakes. These include the [[slowworm]], [[glass snake]], and [[amphisbaenia]]ns.<ref name="Southwest">{{cite book |last3=Browne-Cooper |first3=Robert |last1=Bush |first1=Brian |last2=Maryan |first2=Brad |last4=Robinson |first4=David |title=Reptiles and Frogs in the Bush: Southwestern Australia |year=2007 |publisher=[[University of Western Australia Press]] |isbn=978-1-920694-74-6 |pages=243, 244 }}</ref>

=== Evolution ===
{{Unsolved|biology|Did snakes evolve from burrowing lizards or aquatic lizards?}}
{{Cladogram|title=A family level phylogenetic overview of modern snakes.
|clades={{clade|style=font-size:88.888888%;line-height:100%
 |label1='''Snakes'''
 |1={{clade
 |label1=[[Scolecophidia]]
 |1={{clade
 |1=[[Leptotyphlopidae]]
 |label2=
 |2={{clade
 |1=[[Gerrhopilidae]]
 |2={{clade
 |1=[[Typhlopidae]]
 |2=[[Xenophidiidae]]
 }}
 }}
 }}
 |label2=
 |2={{clade
 |label1=
 |1=[[Anomalepididae]]
 |label2=[[Alethinophidia]]
 |2={{clade
 |1={{clade
 |label1=
 |1={{clade
 |1=[[Aniliidae]]
 |2=[[Tropidophiidae]]
 }}
 |label2=
 |2={{clade
 |1={{clade
 |1={{clade
 |1={{clade
 |1=[[Xenopeltidae]]}}
 |2={{clade
 |1=[[Loxocemidae]]
 |2=[[Pythonidae]]}}
 
 }}
 |2={{clade
 |label1=
 |1=[[Boidae]]
 |label2=
 |2={{clade
 |1=[[Bolyeridae]]
 |2=[[Xenophidiidae]]
 }}
 }}
 }}
 
 |2={{clade
 |label1=
 |1=[[Uropeltidae]]
 |label2=
 |2={{clade
 |1=[[Anomochilidae]]
 |2=[[Cylindrophiidae]]
 }}
 }}
 }}
 }}
 |2={{clade
 |1={{clade
 |1=[[Acrochordidae]]}}
 |2={{clade
 |1={{clade
 |1=[[Xenodermidae]]}}
 |2={{clade
 |1={{clade
 |1=[[Pareidae]]}}
 |2={{clade|1={{clade
 |1=[[Viperidae]]}}
 |2={{clade|1={{clade
 |1=[[Homalopsidae]]}}
 |2={{clade|1={{clade
 |1=[[Colubridae]]}}
 |2={{clade
 |1=[[Lamprophiidae]]
 |2=[[Elapidae]]}}}}}}}}}}}}
 }}
 }}
 }}
 }}
|caption=Note: the tree only indicates relationships, not evolutionary branching times. This is not a definitive tree. It is the best that could be done as of 2024. See original paper for a discussion of difficulties.<ref name="ScienceArticle">{{cite journal |last1=Title |first1=Pascal O. |last2=Singhal |first2=Sonal |last3=Grundler |first3=Michael C. |last4=Costa |first4=Gabriel C. |last5=Pyron |first5=R. Alexander |last6=Colston |first6=Timothy J. |last7=Grundler |first7=Maggie R. |last8=Prates |first8=Ivan |last9=Stepanova |first9=Natasha |last10=Jones |first10=Marc E. H. |last11=Cavalcanti |first11=Lucas B. Q. |last12=Colli |first12=Guarino R. |last13=Di-Poi |first13=Nicolas |last14=Donnellan |first14=Stephen C. |last15=Moritz |first15=Craig |last16=Mesquita |first16=Daniel O. |last17=Pianka |first17=Eric R. |last18=Smith |first18=Stephen A. |last19=Vitt |first19=Laurie J. |last20=Rabosky |first20=Daniel L. |title=The macroevolutionary singularity of snakes |journal=Science |date=23 February 2024 |volume=383 |issue=6685 |pages=918-923 |doi=10.1126/science.adh2449 |pmid=38386744 |bibcode=2024Sci...383..918T |url=https://www.science.org |access-date=22 March 2024|url-access=subscription }}</ref>
}}
}}
The fossil record of snakes is relatively poor because snake [[skeleton]]s are typically small and fragile making [[fossil]]ization uncommon. Fossils readily identifiable as snakes (though often retaining hind limbs) first appear in the fossil record during the [[Cretaceous]] period.<ref>{{cite book |last=Durand |first=J.F. |date=2004 |title=The origin of snakes |series=Geoscience Africa |volume=Abstract |publisher=[[University of the Witwatersrand]] |location=Johannesburg, South Africa |page=187}}</ref> The earliest known true snake fossils (members of the crown group Serpentes) come from the marine [[Simoliophiidae|simoliophiid]]s, the oldest of which is the [[Late Cretaceous]] ([[Cenomanian]] age) ''[[Haasiophis terrasanctus]]'' from the [[West Bank]],<ref name=snake_origin_ecology>{{cite journal |vauthors=Hsiang AY, Field DJ, Webster TH, Behlke AD, Davis MB, Racicot RA, Gauthier JA |title=The origin of snakes: revealing the ecology, behavior, and evolutionary history of early snakes using genomics, phenomics, and the fossil record |journal=BMC Evolutionary Biology |volume=15 |article-number=87 |date = May 2015 |issue=1 |pmid=25989795 |pmc=4438441 |doi=10.1186/s12862-015-0358-5 |bibcode=2015BMCEE..15...87H |doi-access=free }}</ref> dated to between 112 and 94 million years old.<ref name=timetree>{{cite book |last1=Vidal |first1=N. |last2=Rage |first2=J.-C. |last3=Couloux |first3=A. |last4=Hedges |first4=S.B. |date=2009 |chapter=Snakes (Serpentes) |pages=390-397 |editor1-last=Hedges |editor1-first=S. B. |editor2-last=Kumar |editor2-first=S. |title=The Timetree of Life |publisher=[[Oxford University Press]]}}</ref>

Based on genomic analysis it is certain that snakes descend from [[lizard]]s.<ref name="ScienceArticle"/> This conclusion is also supported by [[comparative anatomy]], and the fossil record.<ref name="Meh87">{{cite book |last=Mehrtens |first=J. M. |date=1987 |title=Living Snakes of the World in Color |location=New York |publisher=Sterling Publishers |isbn=0-8069-6460-X}}</ref>{{Rp|11}}<ref name="Sanchez">{{cite web |last=Sanchez |first=Alejandro |name-list-style=vanc |title=Diapsids III: Snakes |work=Father Sanchez's Web Site of West Indian Natural History |url=http://www.kingsnake.com/westindian/metazoa12.html |access-date=November 26, 2007|url-status=live |archive-url=https://web.archive.org/web/20071127163408/http ://www.kingsnake.com/westindian/metazoa12.html |archive-date=November 27, 2007}}</ref><ref name="ScienceArticle"/>

[[Pythonidae|Python]]s and [[Boidae|boa]]s--primitive groups among modern snakes--have vestigial hind limbs: tiny, clawed digits known as [[anal spur]]s, which are used to grasp during mating.<ref name="Meh87"/>{{Rp|11}}<ref name="legs"/> The families [[Leptotyphlopidae]] and [[Typhlopidae]] also possess remnants of the pelvic girdle, appearing as horny projections when visible.

Front limbs are nonexistent in all known snakes. This is caused by the evolution of their [[Hox gene]]s, controlling limb [[morphogenesis]]. The axial skeleton of the snakes' common ancestor, like most other tetrapods, had regional specializations consisting of cervical (neck), thoracic (chest), lumbar (lower back), sacral (pelvic), and caudal (tail) vertebrae. Early in snake evolution, the Hox gene expression in the axial skeleton responsible for the development of the thorax became dominant. As a result, the vertebrae anterior to the hindlimb buds (when present) all have the same thoracic-like identity (except from the [[Atlas (anatomy)|atlas]], [[Axis (anatomy)|axis]], and 1-3 neck vertebrae). In other words, most of a snake's skeleton is an extremely extended thorax. Ribs are found exclusively on the thoracic vertebrae. Neck, lumbar and pelvic vertebrae are very reduced in number (only 2-10 lumbar and pelvic vertebrae are present), while only a short tail remains of the caudal vertebrae. However, the tail is still long enough to be of important use in many species, and is modified in some aquatic and tree-dwelling species.{{Citation needed|date=November 2024}}

Many modern snake groups originated during the [[Paleocene]], alongside the [[adaptive radiation]] of mammals following the extinction of (non-avian) [[dinosaur]]s. The expansion of grasslands in North America also led to an explosive radiation among snakes.<ref name="Fossil Snakes of North America">{{cite book |last1=Holman |first1=J. Alan |name-list-style=vanc |title=Fossil Snakes of North America |date=2000 |publisher=[[Indiana University Press]] |location=Bloomington, IN |isbn=978-0-253-33721-4 |pages=284-323 |edition=First}}</ref> Previously, snakes were a minor component of the North American fauna, but during the Miocene, the number of species and their prevalence increased dramatically with the first appearances of [[viper]]s and [[elapid]]s in North America and the significant diversification of [[Colubridae]] (including the origin of many modern genera such as ''[[Nerodia]]'', ''[[Lampropeltis]]'', ''[[Pituophis]]'', and ''[[Pantherophis]]'').<ref name="Fossil Snakes of North America"/>

=== Fossils ===
There is fossil evidence to suggest that snakes may have evolved from burrowing lizards during the [[Cretaceous|Cretaceous Period]].<ref>{{cite journal |last1=Yi |first1=Hongyu |last2=Norell |first2=Mark A. |title=The burrowing origin of modern snakes |journal=[[Science Advances]] |year=2015 |volume=1 |issue=10 |article-number=e1500743 |doi=10.1126/sciadv.1500743 |pmid=26702436 |pmc=4681343 |bibcode=2015SciA....1E0743Y |s2cid=8912706}}</ref><ref name="EB">{{Cite book |last=Mc Dowell |first=Samuel |title=Evolutionary Biology |chapter=The Evolution of the Tongue of Snakes, and its Bearing on Snake Origins |name-list-style=vanc |year=1972 |volume=6 |pages=191-273 |doi=10.1007/978-1-4684-9063-3_8 |isbn =978-1-4684-9065-7}}</ref> An early fossil snake relative, ''[[Najash rionegrina]]'', was a two-legged burrowing animal with a [[sacrum]], and was fully [[Terrestrial animal|terrestrial]].<ref name=najash>{{cite journal |vauthors=Apesteguia S, Zaher H |title=A Cretaceous terrestrial snake with robust hindlimbs and a sacrum |journal=[[Nature (journal)|Nature]] |volume=440 |issue=7087 |pages=1037-40 |date=April 2006 |pmid=16625194 |doi=10.1038/nature04413 |url=http://www.nature.com/nature/journal/v440/n7087/edsumm/ e060420-11.html |url-status=live |archive-url=https://web.archive.org/web/20071218045427/http ://www.nature.com/nature/journal/v440/n7087/edsumm/e060420-1 1.html |bibcode=2006Natur.440.1037A |s2cid=4417196 |archive-date=December 18, 2007|url-access=subscription }}</ref> ''Najash'', which lived 95 million years ago, also had a skull with several features typical for lizards, but had evolved some of the mobile skull joints that define the flexible skull in most modern snakes. The species did not show any resemblances to the modern burrowing blind snakes, which have often been seen as the most primitive group of extant forms.<ref>{{Cite web |last1=Caldwell |first1=Michael |last2=Palci |first2=Alessandro |editor-first1=Nehal |editor-last1=El-Hadi |url=https://theconversation.com/extraordinary-skull-fossil- reveals-secrets-of-snake-evolution-127307 |title=Extraordinary skull fossil reveals secrets of snake evolution |date=20 November 2019 |doi=10.64628/AAM.ap5d3hu5f |access-date=24 February 2024 |archive-date=24 February 2024 |archive-url=https://web.archive.org/web/20240224202530/http s://theconversation.com/extraordinary-skull-fossil-reveals-s ecrets-of-snake-evolution-127307 |url-status=live }}</ref> One [[extant taxon|extant]] analog of these putative ancestors is the earless monitor ''[[Lanthanotidae|Lanthanotus]]'' of [[Borneo]] (though it is also [[Aquatic animal|semiaquatic]]).<ref name="M2">{{Cite journal |last=Mertens |first=Robert |name-list-style=vanc |title=Lanthanotus: an important lizard in evolution |journal=Sarawak Museum Journal |year=1961 |volume=10 |pages=320-322}}</ref> [[wikt:subterranean|Subterranean]] species evolved bodies streamlined for burrowing, and eventually lost their limbs.<ref name="M2"/> According to this hypothesis, features such as the [[Transparency (optics)|transparent]], fused eyelids ([[brille]]) and loss of external ears evolved to cope with [[fossorial]] difficulties, such as scratched [[cornea]]s and dirt in the ears.<ref name="EB"/><ref name="M2"/> Some primitive snakes are known to have possessed hindlimbs, but their pelvic bones lacked a direct connection to the vertebrae. These include fossil species like ''[[Haasiophis]]'', ''[[Pachyrhachis]]'' and ''[[Eupodophis]]'', which are slightly older than ''[[Najash]]''.<ref name="legs">{{cite web |title=New Fossil Snake With Legs |work=UNEP WCMC Database |publisher=[[American Association for the Advancement of Science]] |location=Washington, D.C. |url=http://www.wildlifenews.co.uk/articles2000/march/march2 500a.htm |access-date=November 29, 2007 |archive-url=https://web.archive.org/web/20071225225126/http ://www.wildlifenews.co.uk/articles2000/march/march2500a.htm |archive-date=December 25, 2007}}
</ref>

This hypothesis was strengthened in 2015 by the discovery of a 113-million-year-old fossil of a four-legged snake in Brazil that has been named ''[[Tetrapodophis|Tetrapodophis amplectus]]''. It has many snake-like features, is adapted for burrowing and its stomach indicates that it was preying on other animals.<ref>{{cite web |title=Four-legged snake ancestor 'dug burrows' |url=https://www.bbc.co.uk/news/science-environment-33621491 |first=Webb |last=Jonathan |name-list-style=vanc |date=July 24, 2014 |publisher=[[BBC|BBC Science & Environment]] |access-date=Jul 24, 2015 |url-status=live|archive-url=https://web.archive.org/web/201 50726051600/http://www.bbc.co.uk/news/science-environment-33 621491 |archive-date=July 26, 2015}}</ref> It is currently uncertain if ''Tetrapodophis'' is a snake or another species, in the [[Squamata|squamate]] order, as a snake-like body has independently evolved at least 26 times. ''Tetrapodophis'' does not have distinctive snake features in its spine and skull.<ref>{{cite web |title=A Fossil Snake With Four Legs |website=[[National Geographic]] |url=http://phenomena.nationalgeographic.com/2015/07/23/a-fo ssil-snake-with-four-legs/ |access-date=July 24, 2015 |first=Ed |last=Yong |name-list-style=vanc |archive-url=https://web.archive.org/web/20150723221358/http ://phenomena.nationalgeographic.com/2015/07/23/a-fossil-snak e-with-four-legs/ |archive-date=July 23, 2015 |date=July 23, 2015}}</ref><ref>{{cite journal |vauthors=Martill DM, Tischlinger H, Longrich NR |title=EVOLUTION. A four-legged snake from the Early Cretaceous of Gondwana |journal=[[Science (journal)|Science]] |volume=349 |issue=6246 |pages=416-9 |date=July 2015 |pmid=26206932 |doi=10.1126/science.aaa9208 |url=https://researchportal.port.ac.uk/portal/en/publication s/a-fourlegged-snake-from-the-early-cretaceous-of-gondwana(b 6583c89-da01-4b9a-9f1e-dc142b9331ff).html |bibcode=2015Sci...349..416M |s2cid=25822461 |access-date=20 March 2020 |archive-date=2 August 2021 |archive-url=https://web.archive.org/web/20210802182407/http s://researchportal.port.ac.uk/portal/en/publications/a-fourl egged-snake-from-the-early-cretaceous-of-gondwana(b6583c89-d a01-4b9a-9f1e-dc142b9331ff).html |url-status=live }}</ref> A study in 2021 places the animal in a group of extinct marine lizards from the Cretaceous period known as [[Dolichosaurus|dolichosaur]]s and not directly related to snakes.<ref>{{Cite web |title=Famous Discovery of Four-Legged Snake Fossil Turns Out to Have a Twist in The Tale |url=https://www.msn.com/en-us/news/technology/famous-discov ery-of-four-legged-snake-fossil-turns-out-to-have-a-twist-in -the-tale/ar-AAQQeEM?ocid=msedgdhp&pc=U531#comments |access-date=November 18, 2021 |website=www.msn.com |language=en-US |archive-date=18 November 2021 |archive-url=https://web.archive.org/web/20211118231312/http s://www.msn.com/en-us/news/technology/famous-discovery-of-fo ur-legged-snake-fossil-turns-out-to-have-a-twist-in-the-tale /ar-AAQQeEM?ocid=msedgdhp&pc=U531#comments |url-status=live }}</ref>

An alternative hypothesis, based on [[Morphology (biology)|morphology]], suggests the ancestors of snakes were related to [[mosasaur]]s--extinct [[aquatic animal|aquatic]] reptiles from the [[Cretaceous]]--forming the clade [[Pythonomorpha]].<ref name="Sanchez"/> According to this hypothesis, the fused, transparent eyelids of snakes are thought to have evolved to combat marine conditions (corneal water loss through osmosis), and the external ears were lost through disuse in an aquatic environment. This ultimately led to an animal similar to today's [[sea snake]]s. In the Late [[Cretaceous]], snakes recolonized land, and continued to diversify into today's snakes. Fossilized snake remains are known from early Late Cretaceous marine sediments, which is consistent with this hypothesis; particularly so, as they are older than the terrestrial ''Najash rionegrina''. Similar skull structure, reduced or absent limbs, and other anatomical features found in both mosasaurs and snakes lead to a positive [[Cladistics|cladistical]] correlation, although some of these features are shared with varanids.{{citation needed|date=June 2016}}

Genetic studies in recent years have indicated snakes are not as closely related to monitor lizards as was once believed--and therefore not to mosasaurs, the proposed ancestor in the aquatic scenario of their evolution. However, more evidence links mosasaurs to snakes than to varanids. Fragmented remains found from the [[Jurassic]] and Early Cretaceous indicate deeper fossil records for these groups, which may potentially refute either hypothesis.<ref>{{cite journal |vauthors=Vidal N, Hedges SB |title=Molecular evidence for a terrestrial origin of snakes |journal=[[Proceedings. Biological Sciences]] |volume=271 |issue=Suppl 4 |pages=S226-9 |date=May 2004 |pmid=15252991 |pmc=1810015 |doi=10.1098/rsbl.2003.0151 |bibcode=2004PBioS.271.0151V }}</ref><ref>{{cite journal |vauthors=Caldwell MW, Nydam RL, Palci A, Apesteguia S |title=The oldest known snakes from the Middle Jurassic-Lower Cretaceous provide insights on snake evolution |journal=[[Nature Communications]] |volume=6 |issue=1 |article-number=5996 |date=January 2015 |pmid=25625704 |doi=10.1038/ncomms6996 |bibcode=2015NatCo...6.5996C |doi-access=free|hdl=11336/37995 |hdl-access=free }}</ref>

<gallery>
File:Tetrapodophis amplectus 3483.jpg|''[[Tetrapodophis]]''
File:Eupodophis at Royal Belgian Institute of Natural Sciences, Brussels.jpg|''[[Eupodophis descouensi]]''
File:Eupodophis descouensi Holotype.jpg|''[[Eupodophis descouensi]]''
File:Eupodophis descouensi Holotype hind leg.jpg|''[[Eupodophis]] descouensi'' hind leg
</gallery>

=== Genetic basis of snake evolution ===
{{Main|Limb development}}
Both fossils and [[Phylogenetics|phylogenetic]] studies demonstrate that snakes evolved from [[lizard]]s, hence the question became which genetic changes led to limb loss in the snake ancestor. Limb loss is actually very common in extant reptiles and has happened dozens of times within [[skink]]s, [[Anguidae|anguids]], and other lizards.<ref>{{cite journal |last1=Bergmann |first1=Philip J. |last2=Morinaga |first2=Gen |title=The convergent evolution of snake-like forms by divergent evolutionary pathways in squamate reptiles |journal=Evolution |date=March 2019 |volume=73 |issue=3 |pages=481-496 |doi=10.1111/evo.13651 |pmid=30460998 }}</ref>

In 2016, two studies reported that limb loss in snakes is associated with DNA mutations in the Zone of Polarizing Activity Regulatory Sequence (ZRS), a regulatory region of the [[sonic hedgehog]] gene which is critically required for limb development. More advanced snakes have no remnants of limbs, but basal snakes such as pythons and boas do have traces of highly reduced, vestigial hind limbs. Python embryos even have fully developed hind limb buds, but their later development is stopped by the DNA mutations in the ZRS.<ref>{{Cite news |url=https://www.theatlantic.com/science/archive/2016/10/wha t-a-legless-mouse-tells-us-about-snake-evolution/504779/ |title=What a Legless Mouse Tells Us About Snake Evolution |newspaper=[[The Atlantic]] |access-date=October 25, 2016 |url-status=live |archive-url=https://web.archive.org/web/20161024222452/http ://www.theatlantic.com/science/archive/2016/10/what-a-legles s-mouse-tells-us-about-snake-evolution/504779/ |archive-date=October 24, 2016}}</ref><ref>{{Cite news |url=http://www.livescience.com/56573-mutation-caused-snakes -to-lose-legs.html |title=Snakes Used to Have Legs and Arms ... Until These Mutations Happened |newspaper=Live Science |access-date=October 22, 2016 |url-status=live |archive-url=https://web.archive.org/web/20161022150634/http ://www.livescience.com/56573-mutation-caused-snakes-to-lose- legs.html |archive-date=October 22, 2016}}</ref><ref>{{cite journal |vauthors=Leal F, Cohn MJ |title=Loss and Re-emergence of Legs in Snakes by Modular Evolution of Sonic hedgehog and HOXD Enhancers |journal=[[Current Biology]] |volume=26 |issue=21 |pages=2966-2973 |date=November 2016 |pmid=27773569 |doi=10.1016/j.cub.2016.09.020 |doi-access=free|bibcode=2016CBio...26.2966L }}</ref><ref>{{cite journal |vauthors=Kvon EZ, Kamneva OK, Melo US, Barozzi I, Osterwalder M, Mannion BJ, Tissieres V, Pickle CS, Plajzer-Frick I, Lee EA, Kato M, Garvin TH, Akiyama JA, Afzal V, Lopez-Rios J, Rubin EM, Dickel DE, Pennacchio LA, Visel A |display-authors=6 |title=Progressive Loss of Function in a Limb Enhancer during Snake Evolution |journal=[[Cell (journal)|Cell]] |volume=167 |issue=3 |pages=633-642.e11 |date=October 2016 |pmid=27768887 |pmc=5484524 |doi=10.1016/j.cell.2016.09.028 |url=}}</ref>

== Distribution ==
[[File:World distribution of snakes.svg|thumb|upright=2.0|Approximate world distribution of snakes]]

There are about 3,900 species of snakes,<ref>{{Cite web |title=The Reptile Database |url=http://www.reptile-database.org/ |access-date=March 6, 2021 |website=www.reptile-database.org |archive-date=2 November 2015 |archive-url=https://web.archive.org/web/20151102083427/http ://reptile-database.org/ |url-status=live }}</ref> ranging as far northward as the Arctic Circle in Scandinavia and southward through Australia.<ref name="Sanchez"/> Snakes can be found on every continent except Antarctica, as well as in the sea, and as high as {{convert|16000|ft|m}} in the [[Himalayan Mountains]] of Asia.<ref name="Sanchez"/><ref name="Con91">{{cite book |last1=Conant |first1=Roger |last2=Collins |first2=Joseph |name-list-style=vanc |author-link=Roger Conant (herpetologist) |title=A Field Guide to Reptiles and Amphibians Eastern/Central North America |publisher=[[Houghton Mifflin Company]] |year=1991 |location=Boston |isbn=978-0-395-58389-0 |url-access=registration |url=https://archive.org/details/fieldguidetorept00cona}}</ref>{{Rp|143}} There are numerous islands from which snakes are absent, such as [[Ireland]], [[Iceland]], and [[New Zealand]]<ref name=Bauchot/><ref name="Con91"/> (although New Zealand's northern waters are infrequently visited by the [[Pelamis platura|yellow-bellied sea snake]] and the [[Laticauda colubrina|banded sea krait]]).<ref name="AucklandMuseum">{{cite web |url=http://www.aucklandmuseum.com/349/natural-history-quest ions |title=Natural History Questions |author1=Natural History Information Centre |author2=Auckland War Memorial Museum |work=Auckland War Memorial Museum {{pipe}} Tamaki Paenga Hira |publisher=[[Auckland War Memorial Museum]] |location=[[Auckland]], New Zealand |at=Q. Are there any snakes in New Zealand? |access-date=April 26, 2012 |archive-url=https://web.archive.org/web/20120712124349/http ://www.aucklandmuseum.com/349/natural-history-questions |archive-date=July 12, 2012}}</ref>

== Biology ==
[[File:Leptotyphlops carlae.jpg|thumb|upright=0.9|An adult Barbados threadsnake, ''[[Leptotyphlops carlae]]'', on an [[Quarter (United States coin)|American quarter dollar]] ]]

===Size===
The now [[Extinction|extinct]] ''[[Titanoboa|Titanoboa cerrejonensis]]'' was {{convert|12.8|m|ft|abbr=on}} in length.<ref name="head">{{cite journal |vauthors=Head JJ, Bloch JI, Hastings AK, Bourque JR, Cadena EA, Herrera FA, Polly PD, Jaramillo CA |display-authors=6 |title=Giant boid snake from the Palaeocene neotropics reveals hotter past equatorial temperatures |journal=[[Nature (journal)|Nature]] |volume=457 |issue=7230 |pages=715-7 |date=February 2009 |pmid=19194448 |doi=10.1038/nature07671 |bibcode=2009Natur.457..715H |s2cid=4381423}}</ref> By comparison, the largest [[Extant taxon|extant]] snakes are the [[reticulated python]], measuring about {{convert|6.95|m|abbr=on}} long,<ref name="SunBear"/> and the [[green anaconda]], which measures about {{convert|5.21|m|abbr=on}} long and is considered the heaviest snake on Earth at {{convert|97.5|kg|lb|abbr=on}}.<ref name="Riv00">{{cite thesis |last=Rivas |first=Jesus Antonio |name-list-style=vanc |year=2000 |title=The life history of the green anaconda (''Eunectes murinus''), with emphasis on its reproductive Biology |degree=[[Doctor of Philosophy|Ph.D.]] |publisher=[[University of Tennessee]] |url=http://www.anacondas.org/diss/disser.pdf |archive-url=https://web.archive.org/web/20160303202240/http ://www.anacondas.org/diss/disser.pdf |archive-date=March 3, 2016 |access-date=December 12, 2014}}</ref>

At the other end of the scale, the smallest extant snake is ''[[Barbados threadsnake|Leptotyphlops carlae]]'', with a length of about {{convert|10.4|cm|in|abbr=on}}.<ref name="zootaxa">{{cite journal |url=http://www.mapress.com/zootaxa/2008/f/zt01841p030.pdf |title=At the lower size limit in snakes: two new species of threadsnakes (Squamata: Leptotyphlopidae: Leptotyphlops) from the Lesser Antilles |first=S. Blair |last=Hedges |name-list-style=vanc |journal=[[Zootaxa]] |volume=1841 |pages=1-30 |date=August 4, 2008 |access-date=August 4, 2008 |url-status=live |archive-url=https://web.archive.org/web/20080813023833/http ://www.mapress.com/zootaxa/2008/f/zt01841p030.pdf |archive-date=August 13, 2008 |doi=10.11646/zootaxa.1841.1.1 |doi-access=free}}</ref> Most snakes are fairly small animals, approximately {{convert|1|m|ft|abbr=on}} in length.<ref>{{cite journal |vauthors=Boback SM, Guyer C |title=Empirical evidence for an optimal body size in snakes |journal=Evolution; International Journal of Organic Evolution |volume=57 |issue=2 |pages=345-51 |date=February 2003 |pmid=12683530 |doi=10.1554/0014-3820(2003)057[0345:EEFAOB]2.0.CO;2 |s2cid=198156987}}</ref>

=== Perception ===
The sensory systems of snakes, particularly those of the Crotalidae family, commonly known as pit vipers, are among the most specialized in the animal kingdom. Pit vipers, which include rattlesnakes and related species, possess all the sensory organs found in other snakes, as well as additional adaptations. These include specialized [[infrared sensing in snakes|infrared-sensitive receptors]], known as pits, located on either side of the head between the nostrils and eyes. These pits, which resemble an additional pair of nostrils, are highly developed and allow pit vipers to detect minute temperature changes. Each pit consists of two cavities: a larger outer cavity positioned just behind and below the nostril, and a smaller inner cavity. These cavities are connected internally by a membrane containing nerves highly sensitive to thermal variations. The forward-facing pits create a combined field of detection, enabling pit vipers to distinguish objects from their surroundings and accurately judge distances. The sensitivity of these pits allows them to detect temperature differences as small as one-third of a degree Fahrenheit. Other infrared-sensitive snakes, such as those in the Boidae family, possess multiple smaller labial pits along the upper lip, just below the nostrils.{{sfn|Cogger|Zweifel|1992|p=180}}

Snakes rely heavily on their sense of smell to track prey. They collect particles from the air, ground, or water using their [[forked tongue]], which are then transferred to the [[vomeronasal organ]] (also known as Jacobson's organ) in the mouth for analysis.{{sfn|Cogger|Zweifel|1992|p=180}} The forked structure of the tongue provides directional information of smell which helps locate prey or predators. In aquatic species, such as the [[anaconda]], the tongue functions efficiently underwater.{{sfn|Cogger|Zweifel|1992|p=180}} When the tongue is retracted, the forked tips are pressed into the cavities of the Jacobson's organ, enabling a combined taste-smell analysis that provides the snake with detailed information about its environment.{{sfn|Campbell|Shaw|1974}}{{page needed|date=April 2024}}{{sfn|Cogger|Zweifel|1992|p=180}}

[[File:Ptyas gab fbi.png|thumb|A line diagram from ''[[The Fauna of British India, Including Ceylon and Burma|The Fauna of British India]]'' by [[George Albert Boulenger|G. A. Boulenger]] (1890), illustrating the terminology of shields on the head of a snake]] Until the mid-20th century, it was widely believed that snakes were unable to hear.{{sfn|Campbell|Shaw|1974|p=19}}<ref name="ReferenceA">{{Cite journal |title=Sound garden: How snakes respond to airborne and groundborne sounds |date=2023 |doi=10.1371/journal.pone.0281285 |doi-access=free |last1=Zdenek |first1=Christina N. |last2=Staples |first2=Timothy |last3=Hay |first3=Chris |last4=Bourke |first4=Lachlan N. |last5=Candusso |first5=Damian |journal=PLOS ONE |volume=18 |issue=2 |article-number=e0281285 |pmid=36787306 |pmc=9928108 |bibcode=2023PLoSO..1881285Z }}</ref> However, snakes possess two distinct auditory systems. One system, the somatic system, involves the transmission of vibrations through ventral skin receptors to the spine. The other system involves vibrations transmitted through the snake's elongated lung to the brain via cranial nerves. Snakes exhibit high sensitivity to vibrations, allowing them to detect even subtle sounds, such as soft speech, in quiet environments.{{sfn|Campbell|Shaw|1974|p=19}}{{Sfn|Cogger|Zweifel|1992|p=180}}<ref name="ReferenceA"/>

Snake vision varies significantly among species. While some snakes have keen eyesight, others can only distinguish light from dark. However, most snakes possess visual acuity sufficient to track movement.<ref>{{cite web |url=http://www.petplace.com/reptiles/reptile-senses-underst anding-their-world/page1.aspx |title=Reptile Senses: Understanding Their World |website=Petplace.com |date=May 18, 2015 |access-date=January 9, 2016 |url-status=live |archive-url=https://web.archive.org/web/20150219062040/http ://www.petplace.com/reptiles/reptile-senses-understanding-th eir-world/page1.aspx |archive-date=February 19, 2015}}</ref> Arboreal snakes generally have better vision than burrowing species. Some snakes, such as the [[Ahaetulla|Asian vine snake]], possess [[binocular vision]], enabling both eyes to focus on the same point. Most snakes focus by moving the [[Lens (anatomy)|lens]] back and forth relative to the [[retina]]. Diurnal snakes typically have round pupils, while many nocturnal species have slit pupils. Most snakes possess three visual pigments, allowing them to perceive two primary colors in daylight. Certain species, such as the [[Hydrophis cyanocinctus|annulated sea snake]] and members of the genus [[Helicops (snake)|Helicops]], have regained significant color vision as an adaptation to their aquatic environments.<ref>{{Cite web |url=https://neurosciencenews.com/color-vision-snake-genetic s-23618/ |title=Sea Snakes Regained Color Vision via Rare Genetic Evolution |date=12 July 2023 |access-date=28 September 2023 |archive-date=28 September 2023 |archive-url=https://web.archive.org/web/20230928181052/http s://neurosciencenews.com/color-vision-snake-genetics-23618/ |url-status=live }}</ref><ref>{{Cite web |url=https://www.newscientist.com/article/2382064-some-sea-s nakes-have-re-evolved-the-ability-to-see-more-colours/ |title=Some sea snakes have re-evolved the ability to see more colours |access-date=28 September 2023 |archive-date=28 September 2023 |archive-url=https://web.archive.org/web/20230928182513/http s://www.newscientist.com/article/2382064-some-sea-snakes-hav e-re-evolved-the-ability-to-see-more-colours/ |url-status=live }}</ref> Research suggests that the last common ancestor of all snakes had [[Ultraviolet|UV]]-sensitive vision. However, many diurnal snakes have evolved lenses that filter out UV light, likely improving [[Contrast (vision)|contrast]] and sharpening their vision.<ref>{{cite web |url=https://www.sciencedaily.com/releases/2016/08/160816182 620.htm |title=Snake eyes: New insights into visual adaptations |date=August 16, 2016 |website=[[ScienceDaily]] |access-date=18 December 2019 |archive-date=18 December 2019 |archive-url=https://web.archive.org/web/20191218105018/http s://www.sciencedaily.com/releases/2016/08/160816182620.htm |url-status=live }}</ref><ref>{{cite journal |url=https://academic.oup.com/mbe/article/33/10/2483/2925599 |title=Visual Pigments, Ocular Filters and the Evolution of Snake Vision |last1=Simoes |first1=Bruno F. |last2=Sampaio |first2=Filipa L. |last3=Douglas |first3=Ronald H. |last4=Kodandaramaiah |first4=Ullasa |last5=Casewell |first5=Nicholas R. |last6=Harrison |first6=Robert A. |last7=Hart |first7=Nathan S. |last8=Partridge |first8=Julian C. |last9=Hunt |first9=David M. |last10=Gower |first10=David J. |display-authors=1 |journal=[[Molecular Biology and Evolution]] |publisher=[[Oxford University Press]] |volume=33 |issue=10 |date=October 2016 |pages=2483-2495 |doi=10.1093/molbev/msw148 |pmid=27535583 |doi-access=free |access-date=1 March 2021 |archive-date=23 March 2021 |archive-url=https://web.archive.org/web/20210323015254/http s://academic.oup.com/mbe/article/33/10/2483/2925599 |url-status=live |hdl=1983/2008257f-b043-4206-a44b-39ebbdd1bea8 |hdl-access=free }}</ref>

=== Skin ===
{{Main|Snake scale}}
The skin of a snake is covered in [[Scale (anatomy)|scales]]. Contrary to the popular notion of snakes being slimy (because of possible confusion of snakes with [[worm]]s), [[snakeskin]] has a smooth, dry texture. Most snakes use specialized belly scales to travel, allowing them to grip surfaces. The body scales may be smooth, [[keeled scales|keeled]], or granular. The eyelids of a snake are transparent "spectacle" scales, also known as [[brille]], which remain permanently closed.{{Citation needed|date=November 2024}}

For a snake, the skin has been modified to its specialized form of locomotion. Between the inner layer and the outer layer lies the dermis, which contains all the pigments and cells that make up the snake's distinguishing pattern and color. The epidermis, or outer layer, is formed of a substance called [[keratin]], which in mammals is the same basic material that forms nails, claws, and hair. The snake's epidermis of keratin provides it with the armor it needs to protect its internal organs and reduce friction as it passes over rocks. Parts of this keratin armor are rougher than others. The less restricted portion overlaps the front of the scale beneath it. Between them lies a folded back connecting material, also of keratin, also part of the epidermis. This folded back material gives as the snake undulates or eats things bigger than the circumference of its body.{{sfn|Campbell|Shaw|1974}}{{page needed|date=April 2024}}

The shedding of scales is called ''[[ecdysis]]'' (or in normal usage, ''molting'' or ''sloughing''). Snakes shed the complete outer layer of skin in one piece.<ref name = "Smith1_30">Smith, Malcolm A. ''[[The Fauna of British India, Including Ceylon and Burma]]''. Vol I, Loricata and Testudines. p. 30.</ref> Snake scales are not discrete, but extensions of the [[epidermis]]--hence they are not shed separately but as a complete outer layer during each molt, akin to a sock being turned inside out.<ref name="RSSlimy">{{cite web|url=http://www.szgdocent.org/resource/rr/c-slimy.htm |title=Are Snakes Slimy? |website=szgdocent.org |archive-url=https://web.archive.org/web/20060805131135/http ://www.szgdocent.org/resource/rr/c-slimy.htm |archive-date=5 August 2006 |url-status=live}}</ref>

Snakes have a wide diversity of skin coloration patterns which are often related to behavior, such as the tendency to have to flee from predators. Snakes that are at a high risk of predation tend to be plain, or have longitudinal stripes, providing few reference points to predators, thus allowing the snake to escape without being noticed. Plain snakes usually adopt active hunting strategies, as their pattern allows them to send little information to prey about motion. Blotched snakes usually use ambush-based strategies, likely because it helps them blend into an environment with irregularly shaped objects, like sticks or rocks. Spotted patterning can similarly help snakes to blend into their environment.<ref name="AllenBaddeley2013">{{cite journal |last1=Allen |first1=William L. |last2=Baddeley |first2=Roland |last3=Scott-Samuel |first3=Nicholas E. |last4=Cuthill |first4=Innes C. |name-list-style=vanc |title=The evolution and function of pattern diversity in snakes |journal=[[Behavioral Ecology (journal)|Behavioral Ecology]] |volume=24 |issue=5 |year=2013 |pages=1237-1250 |issn=1465-7279 |doi=10.1093/beheco/art058 |doi-access=free}}</ref>

The shape and number of scales on the head, back, and belly are often characteristic and used for taxonomic purposes. Scales are named mainly according to their positions on the body. In "advanced" ([[Caenophidia]]n) snakes, the broad belly scales and rows of [[dorsal scale]]s correspond to the [[vertebra]]e, allowing these to be counted without the need for [[dissection]].{{Citation needed|date=November 2024}}

==== Molting ====
[[File:Nerodia sipedon shedding.JPG|thumb|left|A [[common watersnake]] shedding its skin]]
[[Molting]] (or "ecdysis") serves a number of purposes - it allows old, worn skin to be replaced and can be synced to mating cycles, as with other animals. Molting occurs periodically throughout the life of a snake. Before each molt, the snake regulates its diet and seeks defensible shelter. Just before shedding, the skin becomes grey and the snake's eyes turn silvery. The inner surface of the old skin liquefies, causing it to separate from the new skin beneath it. After a few days, the eyes clear and the snake reaches out of its old skin, which splits. The snake rubs its body against rough surfaces to aid in the shedding of its old skin. In many cases, the castaway skin peels backward over the body from head to tail in one piece, like taking the dust jacket off a book, revealing a new, larger, brighter layer of skin which has formed underneath.<ref name="RSSlimy"/><ref name="GenSnakeInfo">{{cite web|url=http://www.sdgfp.info/Wildlife/Snakes/SnakeInfo.htm |title=General Snake Information |website=sdgfp.info |archive-url=https://web.archive.org/web/20071125210255/http ://www.sdgfp.info/Wildlife/Snakes/SnakeInfo.htm |archive-date=November 25, 2007 }}</ref> Renewal of the skin by molting supposedly increases the mass of some animals such as insects, but in the case of snakes this has been disputed.<ref name="RSSlimy"/><ref name="ZooPax3">{{cite web |url=http://whozoo.org/ZooPax/ZPScales_3.htm |title=ZooPax: A Matter of Scale: Part III |website=Whozoo.org |access-date=January 9, 2016 |url-status=live |archive-url=https://web.archive.org/web/20160116034245/http ://whozoo.org/ZooPax/ZPScales_3.htm |archive-date=January 16, 2016}}</ref> Shedding skin can release pheromones and revitalize color and patterns of the skin to increase attraction of mates.<ref>{{Cite journal |last1=Bauwens |first1=Dirk |last2=Van Damme |first2=Raoul |last3=Verheyen |first3=Rudolf F. |date=1989 |title=Synchronization of Spring Molting with the Onset of Mating Behavior in Male Lizards, Lacerta vivipara |journal=[[Journal of Herpetology]] |volume=23 |issue=1 |pages=89-91 |doi=10.2307/1564326 |jstor=1564326 |bibcode=1989JHerp..23...89B |issn=0022-1511 }}</ref>

[[File:Shed skin of a snake.jpg|thumb|Shed skin of a snake]]

Snakes may shed four or five times a year, depending on the weather conditions, food supply, age of the snake, and other factors.{{sfn|Campbell|Shaw|1974}}{{page needed|date=April 2024}}<ref name = "GenSnakeInfo"/> It is theoretically possible to identify the snake from its cast skin if it is reasonably intact.<ref name="RSSlimy"/> Mythological associations of snakes with symbols of [[healing]] and [[medicine]], as pictured in the [[Rod of Asclepius]], are derivative of molting.<ref name=AIM>{{cite journal |vauthors=Wilcox RA, Whitham EM |title=The symbol of modern medicine: why one snake is more than two |journal=Annals of Internal Medicine |volume=138 |issue=8 |pages=673-7 |date=April 2003 |pmid=12693891 |doi=10.7326/0003-4819-138-8-200304150-00016 |citeseerx=10.1.1.731.8485 |s2cid=19125435}}</ref>

One can attempt to identify the sex of a snake when the species is not distinctly [[Sexual dimorphism|sexually dimorphic]] by counting scales. The [[cloaca]] is probed and measured against the [[subcaudal scales]].<ref name="Rosenfeld_11">Rosenfeld (1989), p. 11.</ref> Counting scales determines whether a snake is a male or female, as the [[Hemipenis|hemipenes]] of a male being probed is usually longer.<ref name="Rosenfeld_11"/>{{clarify|reason=Is it really scale counts or are the scales merely used to measure the probe penetration?|date=July 2016}}

=== Skeleton ===
{{main|Snake skeleton}}
[[File:Reticulated python (Python reticulatus) skull 1 (cropped).jpg|thumb|[[Reticulated python]] skull, showing jaw movements when swallowing]]
The skull of a snake differs from a lizards in several ways. Snakes have more flexible jaws, that is, instead of a juncture at the upper and lower jaw, the snake's jaws are connected by a bone hinge that is called the [[quadrate bone]]. Between the two halves of the lower jaw at the chin there is an elastic ligament that allows for a separation. This allows the snake to swallow food larger in proportion to their size and go longer without it, since snakes ingest relatively more in one feeding.{{sfn|Campbell|Shaw|1974|p=11}} Because the sides of the lower jaw can move independently of one another, a snake resting its jaw on a surface has stereo [[Hearing|auditory perception]], used for detecting the position of prey. The jaw-quadrate-[[stapes]] pathway is capable of detecting vibrations on the [[angstrom]] scale, despite the absence of an outer ear and the lack of an [[impedance matching]] mechanism--provided by the [[ossicles]] in other vertebrates.<ref>{{cite journal |vauthors=Friedel P, Young BA, van Hemmen JL |title=Auditory localization of ground-borne vibrations in snakes |journal=[[Physical Review Letters]] |volume=100 |issue=4 |article-number=048701 |date=February 2008 |pmid=18352341 |doi=10.1103/physrevlett.100.048701 |bibcode=2008PhRvL.100d8701F}}</ref><ref>{{cite web |url=http://www.physorg.com/news122123444.html |title=Desert Snake Hears Mouse Footsteps with its Jaw |date=February 13, 2008 |first=Lisa |last=Zyga |name-list-style=vanc |publisher=[[Phys.org]] |url-status=live |archive-url=https://web.archive.org/web/20111010152337/http ://www.physorg.com/news122123444.html |archive-date=October 10, 2011}}</ref> In a snake's skull the brain is well protected. As brain tissues could be damaged through the palate, this protection is especially valuable. The solid and complete [[neurocranium]] of snakes is closed at the front.{{sfn|Campbell|Shaw|1974}}{{page needed|date=April 2024}}<ref>{{cite journal |vauthors=Hartline PH |title=Physiological basis for detection of sound and vibration in snakes |journal=The Journal of Experimental Biology |volume=54 |issue=2 |pages=349-71 |date=April 1971 |doi=10.1242/jeb.54.2.349 |pmid=5553415 |bibcode=1971JExpB..54..349H |url=http://jeb.biologists.org/cgi/reprint/54/2/349.pdf |url-status=live |archive-url=https://web.archive.org/web/20081217012157/http ://jeb.biologists.org/cgi/reprint/54/2/349.pdf |archive-date=December 17, 2008}}</ref>

[[File:Snake Skeletons.jpg|thumb|The skeletons of snakes are radically different from those of most other reptiles (as compared with the [[turtle]] here, for example), consisting almost entirely of an extended ribcage.]]

The skeleton of most snakes consists solely of the skull, [[hyoid]], vertebral column, and ribs, though [[henophidia]]n snakes retain vestiges of the pelvis and rear limbs. The hyoid is a small bone located posterior and ventral to the skull, in the 'neck' region, which serves as an attachment for the muscles of the snake's tongue, as it does in all other [[tetrapod]]s. The vertebral column consists of between 200 and 400 vertebrae, or sometimes more. The body vertebrae each have two ribs articulating with them. The tail vertebrae are comparatively few in number (often less than 20% of the total) and lack ribs. The vertebrae have projections that allow for strong muscle attachment, enabling locomotion without limbs.{{Citation needed|date=November 2024}}

Caudal [[autotomy]] (self-amputation of the tail), a feature found in some lizards, is absent in most snakes.<ref>Cogger, H 1993 Fauna of Australia. Vol. 2A Amphibia and Reptilia. Australian Biological Resources Studies, Canberra.</ref> In the rare cases where it does exist in snakes, caudal autotomy is intervertebral (meaning the separation of adjacent vertebrae), unlike that in lizards, which is intravertebral, i.e. the break happens along a predefined fracture plane present on a vertebra.<ref>{{cite journal |vauthors=Arnold EN |doi=10.1080/00222938400770131 |title=Evolutionary aspects of tail shedding in lizards and their relatives |journal=[[Journal of Natural History]] |year=1984 |volume=18 |issue=1 |pages=127-169|bibcode=1984JNatH..18..127A }}</ref><ref>{{cite journal |vauthors=Ananjeva NB, Orlov NL |year=1994 |title=Caudal autotomy in Colubrid snake ''Xenochrophis piscator'' from Vietnam |journal=Russian Journal of Herpetology |volume=1 |issue=2}}</ref>

In some snakes, most notably boas and pythons, there are vestiges of the hindlimbs in the form of a pair of [[pelvic spur]]s. These small, claw-like protrusions on each side of the cloaca are the external portion of the vestigial hindlimb skeleton, which includes the remains of an ilium and femur.{{Citation needed|date=November 2024}}

Snakes are [[polyphyodont]]s with teeth that are continuously replaced.<ref>{{cite journal |vauthors=Gaete M, Tucker AS |title=Organized emergence of multiple-generations of teeth in snakes is dysregulated by activation of Wnt/beta-catenin signalling |journal=[[PLOS ONE]] |volume=8 |issue=9 |article-number=e74484 |year=2013 |pmid=24019968 |pmc=3760860 |doi=10.1371/journal.pone.0074484 |bibcode=2013PLoSO...874484G |doi-access=free}}</ref>

=== Internal organs ===
{{snake anatomy imagemap}}
Snakes and other non-[[archosaur]] ([[crocodilia]]ns, [[dinosaur]]s + [[bird]]s and allies) reptiles have a three-chambered heart that controls the [[circulatory system]] via the left and right atrium, and one ventricle.<ref>{{cite journal |vauthors=Jensen B, Moorman AF, Wang T |title=Structure and function of the hearts of lizards and snakes |journal=Biological Reviews of the Cambridge Philosophical Society |volume=89 |issue=2 |pages=302-36 |date=May 2014 |pmid=23998743 |doi=10.1111/brv.12056 |s2cid=20035062}}</ref> Internally, the ventricle is divided into three interconnected cavities: the cavum arteriosum, the cavum pulmonale, and the cavum venosum.<ref>{{cite journal |last1=Burggren |first1=Warren W. |name-list-style=vanc |title=Form and Function in Reptilian Circulations |journal=Integrative and Comparative Biology |date=1 February 1987 |volume=27 |issue=1 |pages=5-19 |doi=10.1093/icb/27.1.5 |language=en |issn=1540-7063 |doi-access=free}}</ref> The cavum venosum receives deoxygenated [[blood]] from the right atrium and the cavum arteriosum receives oxygenated blood from the left atrium. Located beneath the cavum venosum is the cavum pulmonale, which pumps blood to the pulmonary trunk.<ref>{{cite journal |last1=Mathur |first1=Prahlad |name-list-style=vanc |title=The anatomy of the reptilian heart. Part I. Varanus monitor (Linn.) |journal=Proc. Ind. Acad. Sci. |date=1944 |volume=Sect. B 20 |pages=1-29 |url=https://www.ias.ac.in/article/fulltext/secb/020/01/0001 -0029 |access-date=May 10, 2019 |archive-date=10 May 2019 |archive-url=https://web.archive.org/web/20190510203803/http s://www.ias.ac.in/article/fulltext/secb/020/01/0001-0029 |url-status=live }}</ref>

The snake's heart is encased in a sac, called the ''[[pericardium]]'', located at the [[:wiktionary:bifurcation|bifurcation]] of the [[bronchi]]. The heart is able to move around, owing to the lack of a diaphragm; this adjustment protects the heart from potential damage when large ingested prey is passed through the [[esophagus]]. The [[spleen]] is attached to the [[gall bladder]] and [[pancreas]] and filters the blood. The [[thymus]], located in fatty tissue above the heart, is responsible for the generation of immune cells in the blood. The cardiovascular system of snakes is unique for the presence of a renal portal system in which the blood from the snake's tail passes through the kidneys before returning to the heart.<ref name="Mader"/>

The circulatory system of a snake is basically like those of any other vertebrae. However, snakes do not regulate internally the temperature of their blood. Called [[Ectotherm|cold-blooded]], snakes actually have blood that is responsive to the varying temperature of the immediate environment. Snakes can regulate blood temperature by moving. Too long in direct sunlight, the snakes' blood is heated beyond tolerance. Left in the ice or snow, the snake may freeze. In temperate zones with pronounced seasonal changes, snakes denning together have adapted to the onslaught of winter.{{sfn|Campbell|Shaw|1974}}{{page needed|date=April 2024}}

The [[vestige|vestigial]] left [[lung]] is often small or sometimes even absent, as snakes' tubular bodies require all of their organs to be long and thin.<ref name="Mader">{{Cite journal |last=Mader |first=Douglas |name-list-style=vanc |title=Reptilian Anatomy |journal=Reptiles |volume=3 |issue=2 |pages=84-93 |date=June 1995}}</ref> In the majority of species, only one lung is functional. This lung contains a vascularized anterior portion and a posterior portion that does not function in gas exchange.<ref name="Mader"/> This 'saccular lung' is used for [[hydrostatic]] purposes to adjust buoyancy in some aquatic snakes and its function remains unknown in terrestrial species.<ref name="Mader"/> Many organs that are paired, such as [[kidneys]] or [[reproductive organs]], are staggered within the body, one located ahead of the other.<ref name="Mader"/>

The snake with its particular arrangement of organs may achieve a greater efficiency.{{compared to?|date=April 2024}} For example, the lung encloses at the part nearest the head and throat an oxygen intake organ, while the other half is used for air reserve. The esophagus-stomach-intestine arrangement is a straight line. It ends where intestinal, urinary, and reproductive tracts open, in a chamber called the cloaca.{{sfn|Campbell|Shaw|1974}}{{page needed|date=April 2024}}

Snakes have no [[lymph node]]s.<ref name="Mader"/>

=== Venom ===
{{See also|Snake venom|Venomous snake|#Bite}}{{Multi image
| image1 = Eastern Milksnake (Lampropeltis triangulum)1.jpg
| image2 = Micrurus pyrrhocryptus 1127095.jpg
| total_width = 250
| direction = vertical
| footer = Innocuous [[milk snakes]] (top) are often mistaken for [[coral snakes]] (bottom) whose venom is deadly to humans.
}}
Cobras, vipers, and closely related species use [[venom]] to immobilize, injure, or kill their prey. The venom is modified [[saliva]], delivered through [[fangs]].<ref name="Meh87" /><ref name=":3">{{Cite journal |last1=Oliveira |first1=Ana L. |last2=Viegas |first2=Matilde F. |last3=da Silva |first3=Saulo L. |last4=Soares |first4=Andreimar M. |last5=Ramos |first5=Maria J. |last6=Fernandes |first6=Pedro A. |date=July 2022 |title=The chemistry of snake venom and its medicinal potential |journal=Nature Reviews Chemistry |language=en |volume=6 |issue=7 |pages=451-469 |doi=10.1038/s41570-022-00393-7 |issn=2397-3358 |pmc=9185726 |pmid=35702592}}</ref>{{Rp|243}} The fangs of 'advanced' venomous snakes like viperids and elapids are hollow, allowing venom to be injected more effectively, and the fangs of [[Snake skeleton#Opisthoglyph|rear-fanged]] snakes such as the boomslang simply have a groove on the posterior edge to channel venom into the wound. Snake venoms are often prey-specific, and their role in self-defense is secondary.<ref name="Meh87" /><ref name=":3" />{{Rp|243}}

Venom, like all salivary secretions, is a predigestant that initiates the breakdown of food into soluble compounds, facilitating proper digestion. Even nonvenomous snakebites (like any animal bite) cause tissue damage.<ref name="Meh87"/><ref name=":3" />{{Rp|209}}
[[File:Snake fang types (cropped).jpg|thumb|Skulls from left to right: Nonvenomous (''[[Pseustes]] sp.''), rear-fanged (''[[Toxicodryas blandingii]]''), elapid (''[[Micropechis|Micropechis ikaheca]]''), viperid (''[[Eastern diamondback rattlesnake|Crotalus adamanteus]]''), venomous lizard (''[[Gila monster|Heloderma suspectum]]''). [[Maxilla]] in red.]]
Certain birds, mammals, and other snakes (such as [[kingsnake]]s) that prey on venomous snakes have developed resistance and even immunity to certain venoms.<ref name="Meh87"/>{{Rp|243}} Venomous snakes include three [[Family (biology)|families]] of snakes, and do not constitute a formal [[Taxonomy (biology)|taxonomic classification]] group.{{Citation needed|date=November 2024}}

The [[Colloquialism|colloquial]] term "poisonous snake" is generally an incorrect label for snakes. A poison is inhaled or ingested, whereas venom produced by snakes is injected into its victim via fangs.{{sfn|Freiberg|Walls|1984|p=125}} There are, however, two exceptions: ''[[Rhabdophis]]'' sequesters toxins from the toads it eats, then secretes them from nuchal glands to ward off predators; and a small unusual population of [[garter snake]]s in the US state of [[Oregon]] retains enough toxins in their livers from ingested [[newt]]s to be effectively poisonous to small local predators (such as [[crow]]s and [[fox]]es).{{sfn|Freiberg|Walls|1984|p=123}}

Snake venoms are complex mixtures of [[protein]]s,<ref name=":3" /> and are stored in [[Venom gland|venom glands]] at the back of the head.{{sfn|Freiberg|Walls|1984|p=123}} In all venomous snakes, these glands open through ducts into grooved or hollow teeth in the upper jaw.<ref name="Meh87"/>{{Rp|243}}{{sfn|Freiberg|Walls|1984|p=125}} The proteins can potentially be a mix of [[neurotoxin]]s (which attack the nervous system), [[hemotoxin]]s (which attack the circulatory system), [[cytotoxin]]s (which attack the cells directly), [[bungarotoxin]]s (related to neurotoxins, but also directly affect muscle tissue), and many other toxins that affect the body in different ways.{{sfn|Freiberg|Walls|1984|p=125}}<ref name=":3" /> Almost all snake venom contains ''[[hyaluronidase]]'', an enzyme that ensures rapid diffusion of the venom.<ref name="Meh87"/>{{Rp|243}}

Venomous snakes that use hemotoxins usually have fangs in the front of their mouths, making it easier for them to inject the venom into their victims.<ref name=":3" />{{sfn|Freiberg|Walls|1984|p=125}} Some snakes that use neurotoxins (such as the [[Boiga dendrophila|mangrove snake]]) have fangs in the back of their mouths, with the fangs curled backwards.{{sfn|Freiberg|Walls|1984|p=126}} This makes it difficult both for the snake to use its venom and for scientists to milk them.{{sfn|Freiberg|Walls|1984|p=125}} Elapids, however, such as cobras and kraits are ''[[proteroglyphous]]''--they possess hollow fangs that cannot be erected toward the front of their mouths, and cannot "stab" like a viper. They must actually bite the victim.<ref name="Meh87"/>{{Rp|242}}

It has been suggested that all snakes may be venomous to a certain degree, with harmless snakes having weak venom and no fangs.<ref name="Fry_2006_earlyevolution">{{cite journal |vauthors=Fry BG, Vidal N, Norman JA, Vonk FJ, Scheib H, Ramjan SF, Kuruppu S, Fung K, Hedges SB, Richardson MK, Hodgson WC, Ignjatovic V, Summerhayes R, Kochva E |display-authors=6 |title=Early evolution of the venom system in lizards and snakes |journal=[[Nature (journal)|Nature]] |volume=439 |issue=7076 |pages=584-8 |date=February 2006 |pmid=16292255 |doi=10.1038/nature04328 |bibcode=2006Natur.439..584F |s2cid=4386245}}</ref> According to this theory, most snakes that are labelled "nonvenomous" would be considered harmless because they either lack a venom delivery method or are incapable of delivering enough to endanger a human. The theory postulates that snakes may have evolved from a common lizard ancestor that was venomous, and also that venomous lizards like the [[gila monster]], [[beaded lizard]], [[monitor lizard]]s, and the now-extinct [[mosasaurs]], may have derived from this same common ancestor. They share this "[[venom clade]]" with various other [[sauria]]n species.{{Citation needed|date=November 2024}}

Venomous snakes are classified in two taxonomic families:

* '''[[Elapidae|Elapid]]s''' - [[cobra]]s including [[king cobra]]s, [[Bungarus|kraits]], [[mamba]]s, [[Austrelaps|Australian copperheads]], [[Hydrophiinae|sea snake]]s, and [[coral snake]]s.{{sfn|Freiberg|Walls|1984|p=126}}
* '''[[Viperidae|Viperids]]''' - vipers, [[rattlesnake]]s, [[Agkistrodon contortrix|copperheads]]/[[Agkistrodon piscivorus|cottonmouths]], and [[Lachesis (genus)|bushmasters]].{{sfn|Freiberg|Walls|1984|p=126}}

There is a third family containing the ''opistoglyphous'' (rear-fanged) snakes (as well as the majority of other snake species):

* '''[[Colubridae|Colubrid]]s''' - [[boomslang]]s, [[tree snake]]s, [[Ahaetulla|vine snakes]], [[Boiga|cat snakes]], although not all colubrids are venomous.<ref name="Meh87"/>{{Rp|209}}{{sfn|Freiberg|Walls|1984|p=126}}

=== Reproduction ===
{{See also|Sexual selection in scaled reptiles}}
[[File:Boa and python.JPG|thumb|''[[Boa imperator]]'' (left) and an [[Albinism|albino]] ''[[Indian python|Python molurus]]'' (right). The former gives birth to live young, while the latter lays eggs.]]
Although a wide range of reproductive modes are used by snakes, all employ [[internal fertilization]]. This is accomplished by means of paired, forked [[hemipenis|hemipenes]], which are stored, inverted, in the male's tail.<ref name="Capula89_117">Capula (1989), p. 117.</ref> The hemipenes are often grooved, hooked, or spined--designed to grip the walls of the female's [[cloaca]].<ref name="AldridgeSever2016">{{cite book |first1=Robert D. |last1=Aldridge |first2=David M. |last2=Sever |name-list-style=vanc |title=Reproductive Biology and Phylogeny of Snakes |url=https://books.google.com/books?id=u-3RBQAAQBAJ |date=April 19, 2016 |publisher=[[CRC Press]] |isbn=978-1-4398-5833-2 |via=[[Google Books]]}}</ref><ref name="Capula89_117"/> The [[Hemipenis#Hemiclitoris|clitoris of the female snake]] consists of two structures located between the cloaca and the scent glands.<ref name="hemic">{{cite journal |last1=Fowell |first1=Megan J. |last2=Sanders |first2=Kate L. |last3=Brennan |first3=Patricia L. R. |last4=Crowe-Riddell |first4=Jenna M. |title=First evidence of hemiclitores in snakes |journal=[[Proceedings of the Royal Society B]] |date=December 21, 2022 |volume=289 |issue=1989 |article-number=20221702 |doi=10.1098/rspb.2022.1702 |pmid=36515117 |pmc=9748774}}</ref>

Most species of snakes lay [[egg (biology)|eggs]] which they abandon shortly after laying. However, a few species (such as the king cobra) construct nests and stay in the vicinity of the hatchlings after incubation.<ref name="Capula89_117"/> Most pythons coil around their egg-clutches and remain with them until they hatch.{{sfn|Cogger|Zweifel|1992|p=186}} A female python will not leave the eggs, except to occasionally bask in the sun or drink water. She will even "shiver" to generate heat to incubate the eggs.{{sfn|Cogger|Zweifel|1992|p=186}}

Some species of snake are [[Ovoviviparity|ovoviviparous]] and retain the eggs within their bodies until they are almost ready to hatch.<ref name="Capula89_118">Capula (1989), p. 118.</ref>{{sfn|Cogger|Zweifel|1992|p=182}} Several species of snake, such as the [[boa constrictor]] and green anaconda, are fully [[Viviparity|viviparous]], nourishing their young through a [[placenta]] as well as a [[yolk sac]]; this is highly unusual among reptiles, and normally found in [[requiem sharks]] or [[placental mammals]].<ref name="Capula89_118"/>{{sfn|Cogger|Zweifel|1992|p=182}} Retention of eggs and live birth are most often associated with colder environments.<ref name="Capula89_117"/>{{sfn|Cogger|Zweifel|1992|p=182}}

[[File:Coast Garter Snake.jpg|thumb|right|The [[garter snake]] has been studied for sexual selection.]]
[[Sexual selection]] in snakes is demonstrated by the 3,000 species that each use different tactics in acquiring mates.<ref name="two">{{cite journal |doi=10.1016/j.anbehav.2003.05.007 |title=Courtship tactics in garter snakes: How do a male's morphology and behaviour influence his mating success? |year=2004 |last1=Shine |first1=Richard |last2=Langkilde |first2=Tracy |last3=Mason |first3=Robert T |name-list-style=vanc |journal=[[Animal Behaviour (journal)|Animal Behaviour]] |volume=67 |issue=3 |pages=477-83 |bibcode=2004AnBeh..67..477S |s2cid=4830666}}</ref> Ritual combat between males for the females they want to [[mating|mate]] with includes topping, a behavior exhibited by most viperids in which one male will twist around the vertically elevated fore body of its opponent and force it downward. It is common for neck-biting to occur while the snakes are entwined.<ref name="three">{{cite journal |doi=10.1016/j.anbehav.2004.03.012 |title=Genetic evidence for sexual selection in black ratsnakes, ''Elaphe obsoleta'' |year=2005 |last1=Blouin-Demers |first1=Gabriel |last2=Gibbs |first2=H. Lisle |last3=Weatherhead |first3=Patrick J. |name-list-style=vanc |journal=[[Animal Behaviour (journal)|Animal Behaviour]] |volume=69 |issue=1 |pages=225-34 |bibcode=2005AnBeh..69..225B |s2cid=3907523}}</ref>

=== Facultative parthenogenesis ===
[[Parthenogenesis]] is a natural form of reproduction in which growth and development of embryos occur without fertilization. ''Agkistrodon contortrix'' (copperhead) and ''Agkistrodon piscivorus'' (cottonmouth) can reproduce by [[Parthenogenesis#Facultative|facultative parthenogenesis]], meaning that they are capable of switching from a [[Sexual reproduction|sexual]] mode of reproduction to an [[Asexual reproduction|asexual]] mode.<ref name=Booth2012>{{cite journal |vauthors=Booth W, Smith CF, Eskridge PH, Hoss SK, Mendelson JR, Schuett GW |title=Facultative parthenogenesis discovered in wild vertebrates |journal=[[Biology Letters]] |volume=8 |issue=6 |pages=983-5 |date=December 2012 |pmid=22977071 |pmc=3497136 |doi=10.1098/rsbl.2012.0666 |bibcode=2012BiLet...8..983B }}</ref> The most likely type of parthenogenesis to occur is [[Parthenogenesis#Automictic|automixis]] with terminal fusion, a process in which two terminal products from the same [[meiosis]] fuse to form a diploid [[zygote]]. This process leads to genome-wide [[Zygosity#Homozygous|homozygosity]], expression of deleterious recessive [[allele]]s, and often to developmental abnormalities. Both captive-born and wild-born copperheads and cottonmouths appear to be capable of this form of parthenogenesis.<ref name=Booth2012 />

Reproduction in [[Squamata|squamate]] reptiles is almost exclusively sexual. Males ordinarily have a ZZ pair of sex-determining chromosomes, and females a ZW pair. However, the Colombian Rainbow boa (''[[Epicrates maurus]]'') can also reproduce by facultative parthenogenesis, resulting in production of WW female progeny. The WW females are likely produced by terminal automixis.<ref name="pmid21868391">{{cite journal |author6-link=Coby Schal |vauthors=Booth W, Million L, Reynolds RG, Burghardt GM, Vargo EL, Schal C, Tzika AC, Schuett GW |display-authors=6 |title=Consecutive virgin births in the new world boid snake, the Colombian rainbow Boa, Epicrates maurus |journal=The Journal of Heredity |volume=102 |issue=6 |pages=759-63 |year=2011 |pmid=21868391 |doi=10.1093/jhered/esr080 |doi-access=free}}</ref>

=== Embryonic development ===
[[File:Mouse_and_Snake_Embryos.jpg|thumb|right|[[Mouse]] embryo 12 day post [[Fertilisation|fertilization]] side by side with [[corn snake]] embryo 2 days post ovo-positioning<ref name=":2" />]]
Snake embryonic development initially follows similar steps as any vertebrate [[embryo]]. The snake embryo begins as a [[zygote]], undergoes rapid cell division, forms a [[germinal disc]], also called a blastodisc, then undergoes [[gastrulation]], [[neurulation]], and [[organogenesis]].<ref name=":0">{{cite journal |last1=Zehr |first1=David R. |date=20 July 1962 |title=Stages in the Normal Development of the Common Garter Snake, Thamnophis sirtalis sirtalis |journal=[[Copeia]] |volume=1962 |issue=2 |pages=322-329 |doi=10.2307/1440898 |jstor=1440898 |bibcode=1962Copei1962..322Z }}</ref> Cell division and proliferation continues until an early snake embryo develops and the typical body shape of a snake can be observed.<ref name=":0" /> Multiple features differentiate the embryologic development of snakes from other vertebrates, two significant factors being the elongation of the body and the lack of limb development.{{Citation needed|date=November 2024}}
[[File:Comparative_somite_creation.jpg|thumb|Diagram illustrating differential [[somite]] size due to difference in [[somitogenesis]] clock oscillation<ref name=":2" />]]
The elongation in snake body is accompanied by a significant increase in [[vertebra]] count (mice have 60 vertebrae, whereas snakes may have over 300).<ref name=":2">{{cite journal |last1=Woltering |first1=Joost M. |title=From Lizard to Snake; Behind the Evolution of an Extreme Body Plan |journal=[[Current Genomics]] |year=2012 |volume=13 |issue=4 |pages=289-299 |doi=10.2174/138920212800793302 |pmid=23204918 |pmc=3394116}}</ref> This increase in vertebrae is due to an increase in [[somite]]s during embryogenesis, leading to an increased number of vertebrae which develop.<ref name=":2" /> Somites are formed at the [[Paraxial mesoderm|presomitic mesoderm]] due to a set of oscillatory genes that direct the [[Clock and wavefront model|somitogenesis clock]]. The snake somitogenesis clock operates at a frequency 4 times that of a mouse (after correction for developmental time), creating more somites, and therefore creating more vertebrae.<ref name=":2" /> This difference in clock speed is believed to be caused by differences in [[LFNG|''Lunatic fringe'' gene]] expression, a gene involved in the somitogenesis clock.<ref>{{Cite journal |last1=Gomez |first1=Celine |last2=Ozbudak |first2=Ertugrul M. |last3=Wunderlich |first3=Joshua |last4=Baumann |first4=Diana |last5=Lewis |first5=Julian |last6=Pourquie |first6=Olivier |date=July 17, 2008 |title=Control of segment number in vertebrate embryos |url=https://www.nature.com/articles/nature07020 |journal=[[Nature (journal)|Nature]] |language=en |volume=454 |issue=7202 |pages=335-339 |doi=10.1038/nature07020 |pmid=18563087 |bibcode=2008Natur.454..335G |s2cid=4373389 |issn=0028-0836 |access-date=30 April 2022 |archive-date=26 March 2023 |archive-url=https://web.archive.org/web/20230326063229/http s://www.nature.com/articles/nature07020 |url-status=live |url-access=subscription }}</ref>

There is ample literature focusing on the limb development/lack of development in snake embryos and the gene expression associated with the different stages. In [[Henophidia|basal snakes]], such as the python, embryos in early development exhibit a hind [[limb bud]] that develops with some cartilage and a cartilaginous pelvic element, however this degenerates before hatching.<ref>{{cite journal |last1=Boughner |first1=Julia C. |last2=Buchtova |first2=Marcela |last3=Fu |first3=Katherine |last4=Diewert |first4=Virginia |last5=Hallgrimsson |first5=Benedikt |last6=Richman |first6=Joy M. |title=Embryonic development of Python sebae - I: Staging criteria and macroscopic skeletal morphogenesis of the head and limbs |journal=Zoology |date=June 2007 |volume=110 |issue=3 |pages=212-230 |doi=10.1016/j.zool.2007.01.005 |pmid=17499493 |bibcode=2007Zool..110..212B }}</ref> This presence of vestigial development suggests that some snakes are still undergoing hind limb reduction before they are eliminated.<ref name=":1">{{cite journal |last1=Leal |first1=Francisca |last2=Cohn |first2=Martin J. |date=January 2018 |title=Developmental, genetic, and genomic insights into the evolutionary loss of limbs in snakes |journal=[[Genesis (journal)|Genesis]] |volume=56 |issue=1 |article-number=e23077 |doi=10.1002/dvg.23077 |pmid=29095557 |s2cid=4510082}}</ref> There is no evidence in basal snakes of forelimb rudiments and no examples of snake forelimb bud initiation in embryo, so little is known regarding the loss of this trait.<ref name=":1" /> Recent studies suggest that hind limb reduction could be due to mutations in enhancers for the [[Sonic hedgehog|SSH]] gene,<ref name=":1" /> however other studies suggested that mutations within the [[Hox gene|Hox Genes]] or their enhancers could contribute to snake limblessness.<ref name=":2" /> Since multiple studies have found evidence suggesting different genes played a role in the loss of limbs in snakes, it is likely that multiple gene mutations had an additive effect leading to limb loss in snakes.<ref>{{Cite journal |last1=Kvon |first1=Evgeny Z. |last2=Kamneva |first2=Olga K. |last3=Melo |first3=Uira S. |last4=Barozzi |first4=Iros |last5=Osterwalder |first5=Marco |last6=Mannion |first6=Brandon J. |last7=Tissieres |first7=Virginie |last8=Pickle |first8=Catherine S. |last9=Plajzer-Frick |first9=Ingrid |last10=Lee |first10=Elizabeth A. |last11=Kato |first11=Momoe |date=October 2016 |title=Progressive Loss of Function in a Limb Enhancer during Snake Evolution |journal=[[Cell (journal)|Cell]] |language=en |volume=167 |issue=3 |pages=633-642.e11 |doi=10.1016/j.cell.2016.09.028 |pmc=5484524 |pmid=27768887}}</ref>

== Behavior and life history ==
[[File:Snake found in wood chips.jpg|thumb|Snake coiled on a stick in [[Oklahoma]]. It was [[brumation|brumating]] in a large pile of wood chips, found by this [[landscaper]] after he bulldozed the pile in late autumn 2018.|197x197px]]
=== Winter dormancy ===
[[File:A snake coiled in the cavity of a tree.jpg|thumb|235x235px|A snaked coiled in the cavity of a tree]]
In regions where winters are too cold for snakes to tolerate while remaining active, local species will enter a period of [[Dormancy#Brumation|brumation]]. Unlike [[Dormancy#Hibernation|hibernation]], in which the dormant mammals are actually asleep, brumating reptiles are awake but inactive. Individual snakes may brumate in burrows, under rock piles, or inside fallen trees, or large numbers of snakes may clump together in [[Hibernaculum (zoology)|hibernacula]].<ref>{{Cite web |last=Gabriel |first=Angeli |date=2022-11-30 |title=Where do snakes go in the winter? |url=https://www.foxweather.com/earth-space/snakes-winter |access-date=2025-04-30 |website=FOX Weather |language=en-US}}</ref>

=== Feeding and diet ===
[[File:Eierschlange frisst Zwergwachtelei.jpg|thumb|upright|[[Dasypeltis|African egg-eating snake]] eating an egg]][[File:PikiWiki Israel 37648 Nature and Colors.jpg|thumb|upright|''[[Dolichophis jugularis]]'' preying on a [[sheltopusik]] ]]
[[File:Eastern Hognose Defense.jpg|thumb|[[Eastern hognose snake|Eastern hognose]] hooding]]
All snakes are [[hypercarnivore|strictly carnivorous]], [[Predation|preying]] on small animals including lizards, frogs, other snakes, small mammals, birds, eggs, fish, snails, worms, and insects.<ref name="Meh87" />{{Rp|81}}<ref name="Sanchez" />{{sfn|Behler|King|1979|p=581}} Snakes cannot bite or tear their food to pieces so must swallow their prey whole. The eating habits of a snake are largely influenced by body size; smaller snakes eat smaller prey. Juvenile pythons might start out feeding on lizards or mice and graduate to small deer or antelope as an adult, for example.{{Citation needed|date=November 2024}}

The snake's [[jaw]] is a complex structure. Contrary to the popular belief that snakes can dislocate their jaws, they have an extremely flexible [[mandible|lower jaw]], the two halves of which are not rigidly attached, and numerous other joints in the skull, which allow the snake to open its mouth wide enough to swallow prey whole, even if it is larger in diameter than the snake itself.{{sfn|Behler|King|1979|p=581}} For example, the [[Dasypeltis|African egg-eating snake]] has flexible jaws adapted for eating eggs much larger than the diameter of its head.<ref name="Meh87" />{{Rp|81}} This snake has no teeth, but does have bony protrusions on the inside edge of its [[Vertebral column|spine]], which it uses to break the shell when eating eggs.<ref name="Meh87" />{{Rp|81}}

The majority of snakes eat a variety of prey animals, but there is some specialization in certain species. [[King cobra]]s and the Australian [[Vermicella annulata|bandy-bandy]] consume other snakes. Species of the family [[Pareidae]] have more teeth on the right side of their mouths than on the left, as they mostly prey on snails and the shells usually spiral clockwise.<ref name="Meh87" />{{Rp|184}}<ref>{{cite journal |vauthors=Hoso M, Asami T, Hori M |title=Right-handed snakes: convergent evolution of asymmetry for functional specialization |journal=[[Biology Letters]] |volume=3 |issue=2 |pages=169-72 |date=April 2007 |pmid=17307721 |pmc=2375934 |doi=10.1098/rsbl.2006.0600 |bibcode=2007BiLet...3..169H }}</ref><ref>{{cite journal |vauthors=Pyron RA, Burbrink FT, Wiens JJ |title=A phylogeny and revised classification of Squamata, including 4161 species of lizards and snakes |journal=[[BMC Evolutionary Biology]] |volume=13 |page=93 |date=April 2013 |issue=1 |pmid=23627680 |pmc=3682911 |doi=10.1186/1471-2148-13-93 |bibcode=2013BMCEE..13...93P |doi-access=free }}</ref>

Some snakes have a venomous bite, which they use to kill their prey before eating it.{{sfn|Behler|King|1979|p=581}}{{sfn|Freiberg|Walls|1984|p p=125-127}} Other snakes kill their prey by [[constriction]],{{sfn|Behler|King|1979|p=581}} while some swallow their prey when it is still alive.<ref name="Meh87" />{{Rp|81}}{{sfn|Behler|King|1979|p=581}}

After eating, snakes become dormant to allow the process of [[digestion]] to take place;<ref name="Rosenfeld_11"/> this is an intense activity, especially after consumption of large prey. In species that feed only sporadically, the entire [[intestine]] enters a reduced state between meals to conserve energy. The digestive system is then 'up-regulated' to full capacity within 48 hours of prey consumption. Being [[ectothermic]] ("cold-blooded"), the surrounding temperature plays an important role in the digestion process. The ideal temperature for snakes to digest food is {{convert|30|degC|degF}}. There is a huge amount of [[metabolism|metabolic]] energy involved in a snake's digestion, for example the surface body temperature of the South American rattlesnake (''[[Crotalus durissus]]'') increases by as much as {{convert|1.2|C-change|sigfig=2}} during the digestive process.<ref>{{cite journal |vauthors=Tattersall GJ, Milsom WK, Abe AS, Brito SP, Andrade DV |title=The thermogenesis of digestion in rattlesnakes |journal=The Journal of Experimental Biology |volume=207 |issue=Pt 4 |pages=579-85 |date=February 2004 |pmid=14718501 |doi=10.1242/jeb.00790 |doi-access=free|bibcode=2004JExpB.207..579T }}</ref> If a snake is disturbed after having eaten recently, it will often [[vomiting|regurgitate]] its prey to be able to escape the perceived threat. When undisturbed, the digestive process is highly efficient; the snake's digestive [[enzymes]] dissolve and absorb everything but the prey's hair (or feathers) and claws, which are excreted along with [[uric acid|waste]].{{Citation needed|date=November 2024}}

=== Hooding and spitting ===
Hooding (expansion of the neck area) is a visual deterrent, mostly seen in cobras (elapids), and is primarily controlled by rib muscles.<ref>{{cite journal |last1=Young |first1=Bruce A. |last2=Kardong |first2=Kenneth V. |title=The functional morphology of hooding in cobras |journal=Journal of Experimental Biology |date=May 2010 |volume=213 |issue=9 |pages=1521-1528 |doi=10.1242/jeb.034447 |pmid=20400637 |bibcode=2010JExpB.213.1521Y }}</ref> Hooding can be accompanied by spitting venom towards the threatening object,<ref>{{cite journal |last1=Young |first1=Bruce A. |last2=Dunlap |first2=Karen |last3=Koenig |first3=Kristen |last4=Singer |first4=Meredith |title=The buccal buckle: the functional morphology of venom spitting in cobras |journal=Journal of Experimental Biology |date=15 September 2004 |volume=207 |issue=20 |pages=3483-3494 |doi=10.1242/jeb.01170 |pmid=15339944 |bibcode=2004JExpB.207.3483Y }}</ref> and producing a specialized sound; hissing. Studies on captive cobras showed that 13-22% of the body length is raised during hooding.<ref>{{Cite journal |first1=Alireza |last1=Nasoori |first2=Delavar |last2=Shahbazzadeh |first3=Toshio |last3=Tsubota |first4=Bruce A. |last4=Young |date=Winter 2016 |title=The defensive behaviour of ''Naja oxiana'', with comments on the visual displays of cobras |number=138 |url=https://www.thebhs.org/publications/the-herpetological- bulletin/issue-number-138-winter-2016/960-04-the-defensive-b ehaviour-of-i-naja-oxiana-i-with-comments-on-the-visual-disp lays-of-cobras |journal=The Herpetological Bulletin |access-date=3 May 2021 |archive-date=3 May 2021 |archive-url=https://web.archive.org/web/20210503094608/http s://www.thebhs.org/publications/the-herpetological-bulletin/ issue-number-138-winter-2016/960-04-the-defensive-behaviour- of-i-naja-oxiana-i-with-comments-on-the-visual-displays-of-c obras |url-status=live }}</ref>

=== Locomotion ===
The lack of limbs does not impede the movement of snakes. They have developed several different modes of locomotion to deal with particular environments. Unlike the gaits of limbed animals, which form a continuum, each mode of snake locomotion is discrete and distinct from the others; transitions between modes are abrupt.{{sfn|Cogger|Zweifel|1992|p=175}}<ref name = "Gray">{{cite journal |vauthors=Gray J |title=The mechanism of locomotion in snakes |journal=The Journal of Experimental Biology |volume=23 |issue=2 |pages=101-20 |date=December 1946 |doi=10.1242/jeb.23.2.101 |pmid=20281580|bibcode=1946JExpB..23..101G }}</ref>

==== Lateral undulation ====
{{Main|Undulatory locomotion}}
[[File:Foot prints of Snake.jpg|thumb|Crawling prints of a snake]]
Lateral undulation is the sole mode of aquatic locomotion, and the most common mode of terrestrial locomotion.<ref name = "Gray"/> In this mode, the body of the snake alternately flexes to the left and right, resulting in a series of rearward-moving "waves".{{sfn|Cogger|Zweifel|1992|p=175}} While this movement appears rapid, snakes have rarely been documented moving faster than two body-lengths per second, often much less.<ref name = "Hekrotte">{{Cite journal |last=Hekrotte |first=Carlton |name-list-style=vanc |title = Relations of Body Temperature, Size, and Crawling Speed of the Common Garter Snake, Thamnophis s. sirtalis |journal=[[Copeia]] |year=1967 |volume=23 |issue=4 |pages=759-763 |doi=10.2307/1441886 |jstor=1441886 |bibcode=1967Copei1967..759H }}</ref> This mode of movement has the same net cost of transport (calories burned per meter moved) as running in lizards of the same mass.<ref name = "Walton">{{cite journal |vauthors=Walton M, Jayne BC, Bennet AF |title=The energetic cost of limbless locomotion |journal=[[Science (journal)|Science]] |volume=249 |issue=4968 |pages=524-7 |date=August 1990 |pmid=17735283 |doi=10.1126/science.249.4968.524 |bibcode=1990Sci...249..524W |s2cid=17065200}}</ref>

Terrestrial lateral undulation is the most common mode of terrestrial locomotion for most snake species.{{sfn|Cogger|Zweifel|1992|p=175}} In this mode, the posteriorly moving waves push against contact points in the environment, such as rocks, twigs, irregularities in the soil, etc.{{sfn|Cogger|Zweifel|1992|p=175}} Each of these environmental objects, in turn, generates a reaction force directed forward and towards the midline of the snake, resulting in forward thrust while the lateral components cancel out.<ref name = "Gray_lissman"/> The speed of this movement depends upon the density of push-points in the environment, with a medium density of about 8{{clarify|What does this refer to? What scale?|date=June 2016}} along the snake's length being ideal.<ref name = "Hekrotte"/> The wave speed is precisely the same as the snake speed, and as a result, every point on the snake's body follows the path of the point ahead of it, allowing snakes to move through very dense vegetation and small openings.<ref name="Gray_lissman">{{cite journal |last1=Gray |first1=J. |last2=Lissmann |first2=H. W. |title=The Kinetics of Locomotion of the Grass-Snake |journal=Journal of Experimental Biology |date=February 1950 |volume=26 |issue=4 |pages=354-367 |doi=10.1242/jeb.26.4.354 |bibcode=1950JExpB..26..354G }}</ref>

When swimming, the waves become larger as they move down the snake's body, and the wave travels backwards faster than the snake moves forwards.<ref name = "Gray2">{{Cite journal |vauthors=Gray J |title=Undulatory propulsion |journal=[[Quarterly Journal of Microscopical Science]] |year=1953 |volume=94 |pages=551-578}}</ref> Thrust is generated by pushing their body against the water, resulting in the observed slip. In spite of overall similarities, studies show that the pattern of muscle activation is different in aquatic versus terrestrial lateral undulation, which justifies calling them separate modes.<ref name = "Jayne1">{{cite journal |vauthors=Jayne BC |title=Muscular mechanisms of snake locomotion: an electromyographic study of lateral undulation of the Florida banded water snake (Nerodia fasciata) and the yellow rat snake (Elaphe obsoleta) |journal=[[Journal of Morphology]] |volume=197 |issue=2 |pages=159-81 |date=August 1988 |pmid=3184194 |doi=10.1002/jmor.1051970204 |bibcode=1988JMorp.197..159J |s2cid=25729192}}</ref> All snakes can laterally undulate forward (with backward-moving waves), but only sea snakes have been observed reversing the motion (moving backwards with forward-moving waves).{{sfn|Cogger|Zweifel|1992|p=175}}

==== Sidewinding ====
{{Main|Sidewinding}}
[[File:Neonate sidewinder sidewinding with tracks unlabeled.jpg|thumb|right|A neonate sidewinder rattlesnake (''[[Crotalus cerastes]]'') sidewinding]]
Most often employed by colubroid snakes ([[colubrids]], [[elapids]], and [[Viperidae|vipers]]) when the snake must move in an environment that lacks irregularities to push against (rendering lateral undulation impossible), such as a slick mud flat, or a sand dune, sidewinding is a modified form of lateral undulation in which all of the body segments oriented in one direction remain in contact with the ground, while the other segments are lifted up, resulting in a peculiar "rolling" motion.{{sfn|Cogger|Zweifel|1992|p=177}}<ref name = "Jayne2">{{Cite journal |vauthors=Jayne BC |title=Kinematics of terrestrial snake locomotion |journal=[[Copeia]] |year=1986 |pages=915-927 |doi=10.2307/1445288 |volume=1986 |issue=4 |jstor=1445288 |bibcode=1986Copei1986..915J }}</ref> The sidewinder moves forward by throwing a loop of itself and then pulling itself up by it. By lowering its head the snake gets leverage, straightening itself out and pressing itself against the ground, it brings itself forward and at an angle that leaves it ready for the next jump. The head and the loop are in effect the two feet upon which the snake walks. The snake's body, appearing roughly perpendicular to its direction, may bewilder the observer, since preconception may lead one to associate snake movement with a head that leads and a body that follows. It appears the sidewinder is going sideways - but precisely where the snake is going, where it wants to go, the head gives clear indication. The snake leaves behind a trail that looks like a series of hooks one after the next. Snakes can move backwards to retreat from an enemy, though they normally do not.{{sfn|Campbell|Shaw|1974}}{{page needed|date=April 2024}} This mode of locomotion overcomes the slippery nature of sand or mud by pushing off with only static portions on the body, thereby minimizing slipping.{{sfn|Cogger|Zweifel|1992|p=177}} The static nature of the contact points can be shown from the tracks of a sidewinding snake, which show each belly scale imprint, without any smearing. This mode of locomotion has very low caloric cost, less than {{frac|1|3}} of the cost for a lizard to move the same distance.<ref name="Walton"/> Contrary to popular belief, there is no evidence that sidewinding is associated with the sand being hot.{{sfn|Cogger|Zweifel|1992|p=177}}

==== Concertina ====
{{Main|Concertina movement}}
When push-points are absent, but there is not enough space to use sidewinding because of lateral constraints, such as in tunnels, snakes rely on concertina locomotion.{{sfn|Cogger|Zweifel|1992|p=175}}<ref name = "Jayne2"/> In this mode, the snake braces the posterior portion of its body against the tunnel wall while the front of the snake extends and straightens.{{sfn|Cogger|Zweifel|1992|p=177}} The front portion then flexes and forms an anchor point, and the posterior is straightened and pulled forwards. This mode of locomotion is slow and very demanding, up to seven times the cost of laterally undulating over the same distance.<ref name="Walton"/> This high cost is due to the repeated stops and starts of portions of the body as well as the necessity of using active muscular effort to brace against the tunnel walls.{{Citation needed|date=November 2024}}

==== Arboreal ====
[[File:Golden tree snake.jpg|thumb|left|[[Golden tree snake]] climbing a flower]]
The movement of snakes in arboreal habitats has only recently been studied.<ref name = "Astley">{{cite journal |vauthors = Astley HC, Jayne BC |title=Effects of perch diameter and incline on the kinematics, performance and modes of arboreal locomotion of corn snakes (Elaphe guttata) |journal=The Journal of Experimental Biology |volume=210 |issue=Pt 21 |pages=3862-72 |date=November 2007 |pmid=17951427 |doi=10.1242/jeb.009050 |s2cid=18129284 |doi-access=|bibcode=2007JExpB.210.3862A }}</ref> While on tree branches, snakes use several modes of locomotion depending on species and bark texture.<ref name="Astley"/> In general, snakes will use a modified form of concertina locomotion on smooth branches, but will laterally undulate if contact points are available.<ref name="Astley"/> Snakes move faster on small branches and when contact points are present, in contrast to limbed animals, which do better on large branches with little 'clutter'.<ref name="Astley"/>

Gliding snakes (''[[Chrysopelea]]'') of Southeast Asia launch themselves from branch tips, spreading their ribs and laterally undulating as they glide between trees.{{sfn|Cogger|Zweifel|1992|p=177}}{{sfn|Freiberg|Walls|1984|p=135}}<ref>{{cite journal |vauthors=Socha JJ |title=Gliding flight in the paradise tree snake |journal=[[Nature (journal)|Nature]] |volume=418 |issue=6898 |pages=603-4 |date=August 2002 |pmid=12167849 |doi=10.1038/418603a |bibcode=2002Natur.418..603S |s2cid=4424131}}</ref> These snakes can perform a controlled glide for hundreds of feet depending upon launch altitude and can even turn in midair.{{sfn|Cogger|Zweifel|1992|p=177}}{{sfn|Freiberg|Walls |1984|p=135}}

==== Rectilinear ====
{{Main|Rectilinear locomotion}}
The slowest mode of snake locomotion is rectilinear locomotion, which is also the only one where the snake does not need to bend its body laterally, though it may do so when turning.{{sfn|Cogger|Zweifel|1992|p=176}} In this mode, the belly scales are lifted and pulled forward before being placed down and the body pulled over them. Waves of movement and stasis pass posteriorly, resulting in a series of ripples in the skin.{{sfn|Cogger|Zweifel|1992|p=176}} The ribs of the snake do not move in this mode of locomotion and this method is most often used by large [[Pythonidae|python]]s, [[Boidae|boa]]s, and [[Viperidae|viper]]s when stalking prey across open ground as the snake's movements are subtle and harder to detect by their prey in this manner.{{sfn|Cogger|Zweifel|1992|p=177}}

==Interactions with humans==
[[File:Snake bite symptoms.png|thumb|Most common symptoms of any kind of snake bite envenomation.<ref name=MedlinePlus/><ref>{{cite web |url=http://www.health-care-clinic.org/diseases/snakebite.ht ml |title=Snake Bite First Aid - Snakebite |website=Health-care-clinic.org |access-date=January 9, 2016 |url-status=live |archive-url=https://web.archive.org/web/20160116034305/http ://www.health-care-clinic.org/diseases/snakebite.html |archive-date=January 16, 2016}}</ref> Furthermore, there is vast variation in symptoms between bites from different types of snakes.<ref name=MedlinePlus>{{cite web |url=https://medlineplus.gov/ency/article/000031.htm |title=Snake bites |website=MedlinePlus.gov |archive-url=https://web.archive.org/web/20101204102457/http ://www.nlm.nih.gov/medlineplus/ency/article/000031.htm |archive-date=December 4, 2010 |url-status=live |access-date=March 9, 2010}} from Tintinalli JE, Kelen GD, Stapcynski JS, eds. ''Emergency Medicine: A Comprehensive Study Guide''. 6th ed. New York, NY: McGraw Hill; 2004. Update Date: 2/27/2008. Updated by: Stephen C. Acosta, MD, Department of Emergency Medicine, Portland VA Medical Center, Portland, OR. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.</ref>]]

=== Bite ===
{{Main|Snakebite}}
[[File:ViperaBerusFang.JPG|thumb|right|''[[Vipera berus]]'', one fang in glove with a small venom stain, the other still in place]]
Snakes do not ordinarily prey on humans. Unless startled or injured, most snakes prefer to avoid contact and will not attack humans. With the exception of large constrictors, nonvenomous snakes are not a threat to humans. The bite of a nonvenomous snake is usually harmless; their teeth are not adapted for tearing or inflicting a deep puncture wound, but rather grabbing and holding. Although the possibility of infection and tissue damage is present in the bite of a nonvenomous snake, venomous snakes present far greater hazard to humans.<ref name="Meh87"/>{{Rp|209}} The [[World Health Organization]] (WHO) lists [[snakebite]] under the "other neglected conditions" category.<ref>{{cite web |last1=WHO |title=The 17 neglected tropical diseases |url=https://www.who.int/neglected_diseases/diseases/en/ |website=WHO |publisher=[[World Health Organization]] |access-date=October 24, 2014 |url-status=live |archive-url=https://web.archive.org/web/20140222035302/http ://www.who.int/neglected_diseases/diseases/en/ |archive-date=February 22, 2014}}</ref>

Documented deaths resulting from snake bites are uncommon. Nonfatal bites from venomous snakes may result in the need for amputation of a limb or part thereof. Of the roughly 725 species of venomous snakes worldwide, only 250 are able to kill a human with one bite. Australia averages only one fatal snake bite per year. In [[India]], 250,000 snakebites are recorded in a single year, with as many as 50,000 recorded initial deaths.<ref name="Sinha">{{Cite news |last=Sinha |first=Kounteya |name-list-style=vanc |title=No more the land of snake charmers... |newspaper=[[The Times of India]] |date=July 25, 2006 |url=http://timesofindia.indiatimes.com/articleshow/1803026. cms |url-status=live |archive-url=https://web.archive.org/web/20110811133738/http ://articles.timesofindia.indiatimes.com/2006-07-25/india/278 15969_1_snake-bites-russell-s-viper-krait-cobra |archive-date=August 11, 2011}}</ref> The WHO estimates that on the order of 100,000 people die each year as a result of snake bites, and around three times as many amputations and other permanent disabilities are caused by snakebites annually.<ref>{{Cite web |url=https://www.who.int/mediacentre/factsheets/fs337/en/ |title=Snakebite envenoming |website=[[World Health Organization]] |language=en-GB |access-date=October 27, 2017 |url-status=live |archive-url=https://web.archive.org/web/20170418105431/http ://www.who.int/mediacentre/factsheets/fs337/en/ |archive-date=April 18, 2017}}</ref>

The health of people is seriously threatened by snakebites, especially in areas where there is a great diversity of snakes and little access to medical care such as the Amazon Rainforest region in South America.<ref>{{Cite web |title=The Amazon Rainforest |url=https://education.nationalgeographic.org/resource/amazo n-rainforest |access-date=2024-03-23 |website=education.nationalgeographic.org |language=en}}</ref> Snakebite is classified by the World Health Organization (WHO) as "other neglected conditions".<ref name=":02">{{Cite web |title=Snakebite |url=https://www.who.int/health-topics/snakebite |access-date=2024-03-23 |website=www.who.int |language=en}}</ref> Although there aren't many recorded snakebite deaths, the bites can cause serious complications and permanent impairments.<ref name=":02" /> The most successful treatment for snakebites is still antivenom, which is made from snake venom.<ref name=":02" /> However, access to antivenom differs greatly by location, with rural areas frequently experiencing difficulties with both cost and availability.<ref name=":12">{{cite journal |last1=Warrell |first1=David A |title=Snake bite |journal=The Lancet |date=January 2010 |volume=375 |issue=9708 |pages=77-88 |doi=10.1016/S0140-6736(09)61754-2 |pmid=20109866 }}</ref> Clinical studies, serum preparation, and venom extraction are among the intricate procedures involved in the manufacturing of antivenom.<ref name=":12" /> The development of alternative treatments and increased accessibility and affordability of antivenom are essential for reducing the global impact of snake bites on human populations.<ref>{{Cite journal |last1=Williams |first1=David J. |last2=Faiz |first2=Mohd Abul |last3=Abela-Ridder |first3=Bernadette |last4=Ainsworth |first4=Stuart |last5=Bulfone |first5=Tommaso C. |last6=Nickerson |first6=Andrea D. |last7=Habib |first7=Abdulrazaq G. |last8=Junghanss |first8=Thomas |last9=Fan |first9=Hui Wen |last10=Turner |first10=Michael |last11=Harrison |first11=Robert A. |last12=Warrell |first12=David A. |date=2019-02-21 |title=Strategy for a globally coordinated response to a priority neglected tropical disease: Snakebite envenoming |journal=PLOS Neglected Tropical Diseases |language=en |volume=13 |issue=2 |article-number=e0007059 |doi=10.1371/journal.pntd.0007059 |doi-access=free |issn=1935-2735 |pmc=6383867 |pmid=30789906}}</ref>

=== Snake charmers ===
{{Main|Snake charming}}
[[File:Snake in basket.jpg|thumb|upright|right|The [[Indian cobra]] is the most common subject of snake charmings.]] 
In some parts of the world, especially in India, snake charming is a roadside show performed by a charmer. In such a show, the snake charmer carries a basket containing a snake that he seemingly charms by playing tunes with his flutelike musical instrument, to which the snake responds.<ref name="Bagla"/> The snake is in fact responding to the movement of the flute, not the sound it makes, as snakes lack external ears (though they do have internal ears).<ref name="Bagla">{{cite news |last=Bagla |first=Pallava |name-list-style=vanc |title=India's Snake Charmers Fade, Blaming Eco-Laws, TV |date=April 23, 2002 |work=[[National Geographic]] News |url=http://news.nationalgeographic.com/news/2002/04/0417_02 0423_snakecharm_2.html |access-date=November 26, 2007 |archive-url=https://web.archive.org/web/20071218213538/http ://news.nationalgeographic.com/news/2002/04/0417_020423_snak echarm_2.html |archive-date=December 18, 2007}}</ref>

The [[Wildlife Protection Act, 1972|Wildlife Protection Act of 1972]] in India technically prohibits snake charming on the grounds of reducing animal cruelty. Other types of snake charmers use a snake and [[mongoose]] show, where the two animals have a mock fight; however, this is not very common, as the animals may be seriously injured or killed. Snake charming as a profession is dying out in India because of competition from modern forms of entertainment and environment laws proscribing the practice. Many Indians have never seen snake charming and it is becoming a folktale of the past.<ref name="Bagla"/><ref>{{Cite news |last=Harding |first=Luke |name-list-style=vanc |url=https://www.theguardian.com/world/2002/apr/02/worlddisp atch.lukeharding |title=Snake tricks lose their charm |date=April 2, 2002 |work=[[The Guardian]] |access-date=April 16, 2020 |archive-date=16 May 2020 |archive-url=https://web.archive.org/web/20200516141126/http s://www.theguardian.com/world/2002/apr/02/worlddispatch.luke harding |url-status=live }}</ref><ref>{{Cite news |last=Chandra |first=Sharmila |name-list-style=vanc |url=https://www.indiatoday.in/magazine/indiascope/story/198 91231-indias-snake-charmers-sway-on-the-edge-of-extinction-8 16887-1989-12-31 |title=India's snake-charmers sway on the edge of extinction |date=November 12, 2013 |work=[[India Today]] |access-date=April 16, 2020 |archive-date=3 May 2020 |archive-url=https://web.archive.org/web/20200503031951/http s://www.indiatoday.in/magazine/indiascope/story/19891231-ind ias-snake-charmers-sway-on-the-edge-of-extinction-816887-198 9-12-31 |url-status=live }}</ref><ref>{{cite book|url=https://books.google.com/books?id=BumyQJ14n8sC&pg=P A482 |title=International Wildlife Encyclopedia |last1=Burton |last2=Burton |first1=Maurice |first2=Robert |year=2002 |volume=4 |edition=3rd |section=Snake charmer's bluff |page=482 |publisher=Marshall Cavendish |isbn=978-0-7614-7270-4 |archive-url=https://web.archive.org/web/20160818204631/http s://books.google.com/books?id=BumyQJ14n8sC&pg=PA482 |archive-date=August 18, 2016 |url-status=live |via=[[Google Books]]}}</ref>

=== Trapping ===
The ''Irulas'' tribe of [[Andhra Pradesh]] and [[Tamil Nadu]] in India have been hunter-gatherers in the hot, dry plains forests, and have practiced the art of snake catching for generations. They have a vast knowledge of snakes in the field. They generally catch the snakes with the help of a simple stick. Earlier, the ''Irulas'' caught thousands of snakes for the snake-skin industry. After the complete ban of the snake-skin industry in India and protection of all snakes under the [[Wildlife Protection Act of 1972|Indian Wildlife (Protection) Act 1972]], they formed the Irula Snake Catcher's Cooperative and switched to catching snakes for removal of venom, releasing them in the wild after four extractions. The venom so collected is used for producing life-saving antivenom, biomedical research and for other medicinal products.<ref name="Whitaker et al.">{{cite book |last1=Whitaker |first1=Romulus |last2=Captain |first2=Ashok |title=Snakes of India: The Field Guide |date=2004 |pages=11-13}}</ref> The ''Irulas'' are also known to eat some of the snakes they catch and are very useful in rat extermination in the villages.{{Citation needed|date=November 2024}}

Despite the existence of snake charmers, there have also been professional snake catchers or [[Wrangler (profession)|wranglers]]. Modern-day snake trapping involves a [[herpetologist]] using a long stick with a V-shaped end. Some television show hosts, like [[Bill Haast]], [[Austin Stevens]], [[Steve Irwin]], and [[Jeff Corwin]], prefer to catch them using bare hands.{{Cn|date=November 2024}}
<!-- NOTE: Austin Stevens only catches nonvenomous snakes with his bare hands. He uses snake tongs otherwise. -->
<!--
At least one tribe uses a specialized form of snake catching as a rite of passage to manhood.{{Citation needed|date=February 2007}} The young man of interest will wrap his leg heavily in some type of cloth all the way to the inseam. He will then stick his leg in a burrow containing a large python, typically a [[Python reticulatus|reticulated python]]. After the snake swallows most of his leg, several other members of the tribe will pull him out of the hole along with the snake. The snake is then killed and the man's leg removed from the snake. These snakes can be over {{convert|7|m|ft|abbr=off|sp=us}} long, and it is possible for the man to have his leg dislocated. The scent of a prey animal may be used to help convince the snake to swallow the leg. Snakes have a single-tract digestive system, but the digestion process is actually much slower.

Commented this paragraph out till the tribe is identified and a reference given.
-->

=== Consumption ===
[[File:Snake meat.jpg|thumb|right|Snake meat, in a Taipei restaurant]]
Consuming snake flesh and related goods is a reflection of many cultures around the world, especially in Asian nations like China, Taiwan, Thailand, Indonesia, Vietnam, and Cambodia. Because of its supposed health benefits and aphrodisiac qualities, snake meat is frequently regarded as a delicacy and ingested.<ref name=":23">{{Cite web |title=The wine that comes with added bite |url=https://www.bbc.com/travel/article/20151113-the-wine-th at-comes-with-added-bite |access-date=2024-03-08 |website=www.bbc.com|date=25 February 2022 }}</ref> It is customary to drink wine laced with snake blood in an attempt to increase virility and vigor.<ref name=":23" /> Traditional Chinese medicine holds that snake wine, a traditional beverage infused with whole snakes, offers medicinal uses.<ref name=":23" /> Snake wine's origins are in Chinese culture. However, using snake goods creates moral questions about conservation and animal welfare.<ref name=":33">{{Cite web |title=Articles tagged as Snakes {{!}} Smithsonian Magazine |url=https://www.smithsonianmag.com/tag/snakes/ |access-date=2024-03-08 |website=www.smithsonianmag.com}}</ref> It is important to pay attention to and regulate the sustainable harvesting of snakes for human food, particularly in areas where snake populations are in decline as a result of habitat degradation and overexploitation.<ref name=":33" />

=== Pets ===
In the [[Western world]], some snakes are kept as pets, especially docile species such as the [[ball python]] and [[corn snake]]. To meet the demand, a [[herpetoculture|captive breeding]] industry has developed. Snakes bred in captivity are considered preferable to specimens caught in the wild and tend to make better pets.<ref>{{cite book |last1=Ernest |first1=Carl |first2=George R. |last2=Zug |first3=Molly Dwyer |last3=Griffin |name-list-style=vanc |title=Snakes in Question: The Smithsonian Answer Book |publisher=Smithsonian Books |year=1996 |location=Washington, D.C. |page=[https://archive.org/details/snakesinquestion00erns/pa ge/203 203] |isbn=978-1-56098-648-5 |url=https://archive.org/details/snakesinquestion00erns/page/203}}</ref> Compared with more traditional types of companion animal, snakes can be very low-maintenance pets; they require minimal space, as most common species do not exceed {{convert|5|ft|m}} in length, and can be fed relatively infrequently--usually once every five to fourteen days. Certain snakes have a lifespan of more than 40 years if given proper care.{{cn|date=November 2024}}

=== Symbolism ===
{{Main|Serpent (symbolism)}}
[[File:Golden Uraes Cobra Tutankhamun's Throne.jpg|thumb|right|The reverse side of the throne of Pharaoh [[Tutankhamun]] with four golden uraeus cobra figures. Gold with [[lapis lazuli]]; [[Valley of the Kings]], Thebes (1347-37 BCE).]]
[[File:Longane, Sicily.JPG|thumb|right|upright=0.65|Snakes composing a bronze [[kerykeion]] from the mythical [[Longanus]] river in Sicily]]

In [[Mesopotamia|ancient Mesopotamia]], [[Nirah]], the messenger god of [[Istaran]], was represented as a serpent on ''[[kudurru]]s'', or [[boundary marker|boundary stones]].<ref name="BlackGreen1992">{{cite book |last1=Black |first1=Jeremy |first2=Anthony |last2=Green |name-list-style=vanc |title=Gods, Demons and Symbols of Ancient Mesopotamia: An Illustrated Dictionary |location=Austin, Texas |publisher=[[University of Texas Press]] |year=1992 |isbn=978-0-7141-1705-8 |pages=166-168}}</ref> Representations of two intertwined serpents are common in [[Sumerian art]] and Neo-Sumerian artwork<ref name="BlackGreen1992"/> and still appear sporadically on [[cylinder seal]]s and amulets until as late as the thirteenth century BC.<ref name="BlackGreen1992"/> The horned viper (''[[Cerastes cerastes]]'') appears in [[Kassites|Kassite]] and [[Neo-Assyrian Empire|Neo-Assyrian]] kudurrus<ref name="BlackGreen1992"/> and is invoked in [[Assyria]]n texts as a magical protective entity.<ref name="BlackGreen1992"/> A dragon-like creature with horns, the body and neck of a snake, the forelegs of a lion, and the hind-legs of a bird appears in Mesopotamian art from the Akkadian Period until the [[Hellenistic Period]] (323 BC-31 BC).<ref name="BlackGreen1992"/> This creature, known in [[Akkadian language|Akkadian]] as the ''[[mushussu]]'', meaning "furious serpent", was used as a symbol for particular deities and also as a general protective emblem.<ref name="BlackGreen1992"/> It seems to have originally been the attendant of the Underworld god [[Ninazu]],<ref name="BlackGreen1992"/> but later became the attendant to the [[Hurrian religion|Hurrian]] storm-god [[Tishpak]], as well as, later, Ninazu's son [[Ningishzida]], the Babylonian [[national god]] [[Marduk]], the scribal god [[Nabu]], and the Assyrian national god Ashur.<ref name="BlackGreen1992"/>

In [[History of Egypt|Egyptian history]], the snake occupies a primary role with the Nile cobra adorning the crown of the pharaoh in ancient times. It was [[snake worship|worshipped]] as one of the gods and was also used for sinister purposes: murder of an adversary and ritual suicide ([[Cleopatra VII of Egypt|Cleopatra]]).<ref>{{cite web|url=https://www.history.com/news/cleopatra-suicide-snake -bite|title=Did Cleopatra Really Die by Snake Bite?|author=Sarah Pruitt|date=March 10, 2020|website=History.com}}</ref> The [[ouroboros]] was a well-known [[ancient Egypt]]ian symbol of a serpent swallowing its own tail.<ref name="Hornung">{{cite book |last=Hornung |first=Erik |date=2001 |title=The Secret Lore of Egypt: Its Impact on the West |url=https://books.google.com/books?id=SB_y56Vlz5kC&q=Ourobo ros+dragon+ancient+Egypt&pg=PA75 |location=Ithaca, New York and London, England |publisher=[[Cornell University Press]] |isbn=978-0-8014-3847-9 |pages=13, 44 |via=[[Google Books]] |access-date=20 October 2020 |archive-date=19 February 2024 |archive-url=https://web.archive.org/web/20240219210357/http s://books.google.com/books?id=SB_y56Vlz5kC&q=Ouroboros+drago n+ancient+Egypt&pg=PA75#v=snippet&q=Ouroboros%20dragon%20anc ient%20Egypt&f=false |url-status=live }}</ref> The precursor to the ouroboros was the "Many-Faced",<ref name="Hornung"/> a serpent with five heads, who, according to the [[Amduat]], the oldest surviving [[Book of the Dead|Book of the Afterlife]], was said to coil around the corpse of the sun god Ra protectively.<ref name="Hornung"/> The earliest surviving depiction of a "true" ouroboros comes from the gilded shrines in [[KV62|the tomb]] of [[Tutankhamun]].<ref name="Hornung"/> In the early centuries AD, the ouroboros was adopted as a symbol by [[Gnosticism|Gnostic]] Christians<ref name="Hornung"/> and chapter 136 of the ''[[Pistis Sophia]]'', an early Gnostic text, describes "a great dragon whose tail is in its mouth".<ref name="Hornung"/> In medieval alchemy, the ouroboros became a typical western dragon with wings, legs, and a tail.<ref name="Hornung"/>

In the [[Bible]], King [[Nahash of Ammon]], whose name means "Snake", is depicted very negatively, as a particularly cruel and despicable enemy of the ancient Hebrews.{{Citation needed|date=November 2024}}

[[File:Medusa by Carvaggio.jpg|thumb|upright|''[[Medusa (Caravaggio)|Medusa]]'' (1597) by the Italian artist [[Caravaggio]] ]]
The ancient Greeks used the [[Gorgoneion]], a depiction of a hideous face with serpents for hair, as an [[Apotropaic magic|apotropaic symbol]] to ward off evil.<ref>{{cite journal |last=Phinney |first=Edward Jr. |date=1971 |title=Perseus' Battle with the Gorgons |journal=Transactions and Proceedings of the American Philological Association |volume=102 |pages=445-463 |doi=10.2307/2935950 |jstor=2935950}}</ref> In a [[Greek mythology|Greek myth]] described by Pseudo-Apollodorus in his ''[[Bibliotheca (Pseudo-Apollodorus)|Bibliotheca]]'', [[Medusa]] was a [[Gorgon]] with serpents for hair whose gaze turned all those who looked at her to stone and was slain by the hero [[Perseus]].<ref>{{cite book |last=Kinsley |first=David |date=1989 |title=The Goddesses' Mirror: Visions of the Divine from East and West |location=Albany, New York |publisher=[[New York State University Press]] |isbn=978-0-88706-836-2 |url=https://books.google.com/books?id=82oFlfs3MpwC&q=Athena +pallas+goddess&pg=PA142 |page=151 |via=[[Google Books]] |access-date=20 October 2020 |archive-date=25 April 2023 |archive-url=https://web.archive.org/web/20230425062842/http s://books.google.com/books?id=82oFlfs3MpwC&q=Athena+pallas+g oddess&pg=PA142 |url-status=live }}</ref><ref>{{cite book |last=Deacy |first=Susan |author-link=Susan Deacy |title=Athena |location=New York City, New York and London, England |publisher=[[Routledge]] |date=2008 |isbn=978-0-415-30066-7 |url=https://books.google.com/books?id=kIiCAgAAQBAJ&q=Athena +and+Ares+Darmon&pg=PA163 |via=[[Google Books]] |access-date=20 October 2020 |archive-date=19 February 2024 |archive-url=https://web.archive.org/web/20240219205833/http s://books.google.com/books?id=kIiCAgAAQBAJ&q=Athena+and+Ares +Darmon&pg=PA163#v=snippet&q=Athena%20and%20Ares%20Darmon&f= false |url-status=live }}</ref><ref>Pseudo-Apollodorus, ''Bibliotheca'' 2.37, 38, 39</ref> In the Roman poet [[Ovid]]'s ''[[Metamorphoses]]'', [[Medusa]] is said to have once been a beautiful priestess of [[Athena]], whom Athena turned into a serpent-haired monster after she was raped by the god [[Poseidon]] in Athena's temple.<ref>{{cite journal |last=Seelig |first=Beth J. |date=August 2002 |title=The Rape of Medusa in the Temple of Athena: Aspects of Triangulation in the Girl |journal=The International Journal of Psychoanalysis |volume=83 |issue=4 |pages=895-911 |doi=10.1516/3NLL-UG13-TP2J-927M |pmid=12204171 |s2cid=28961886}}</ref> In another myth referenced by the [[Boeotia]]n poet [[Hesiod]] and described in detail by Pseudo-Apollodorus, the hero [[Heracles]] is said to have slain the [[Lernaean Hydra]],<ref name="West2007">{{cite book |last=West |first=Martin Litchfield |author-link=Martin Litchfield West |title=Indo-European Poetry and Myth|url=https://archive.org/details/indoeuropeanpoet00west |url-access=limited |date=2007 |publisher=[[Oxford University Press]] |location=Oxford, England |isbn=978-0-19-928075-9 |page=[https://archive.org/details/indoeuropeanpoet00west/pa ge/n272 258]}}</ref><ref name="Ogden2013">{{cite book |last=Ogden |first=Daniel |date=2013 |title=''Drakon'': Dragon Myth and Serpent Cult in the Ancient Greek and Roman Worlds |url=https://books.google.com/books?id=FQ2pAK9luwkC&q=ancien t+Greek+dragons |location=Oxford, England |publisher=[[Oxford University Press]] |isbn=978-0-19-955732-5 |pages=28-29 |via=[[Google Books]] |access-date=20 October 2020 |archive-date=19 February 2024 |archive-url=https://web.archive.org/web/20240219210917/http s://books.google.com/books?id=FQ2pAK9luwkC&q=ancient+Greek+d ragons#v=snippet&q=ancient%20Greek%20dragons&f=false |url-status=live }}</ref> a multiple-headed serpent which dwelt in the swamps of [[Lerna]].<ref name="West2007"/><ref name="Ogden2013"/>

The legendary account of the foundation of [[Ancient Thebes (Boeotia)|Thebes]] mentioned a monster snake guarding the spring from which the new settlement was to draw its water. In fighting and killing the snake, the companions of the founder [[Cadmus]] all perished--leading to the term "[[Cadmean victory]]" (i.e. a victory involving one's own ruin).<ref>{{cite book|url=https://books.google.com/books?id=Gf5QEAAAQBAJ|titl e=Reflections in a Serpent's Eye Thebes in Ovid's Metamorphoses|author=Micaela Janan|date=2009|isbn=978-0-19-157225-8|publisher=OUP Oxford}}</ref>

[[File:Rod of asclepius.jpg|thumb|upright|[[Rod of Asclepius]], in which the snake, through [[ecdysis]], symbolizes healing]]
Three medical symbols involving snakes that are still used today are [[Bowl of Hygieia]], symbolizing pharmacy, and the [[Caduceus]] and [[Rod of Asclepius]], which are symbols denoting medicine in general.<ref name=AIM/>

One of the etymologies proposed for the common female first name ''[[Linda (given name)|Linda]]'' is that it might derive from Old German ''Lindi'' or ''Linda'', meaning a serpent.{{cn|date=November 2024}}

India is often called the land of snakes and is steeped in tradition regarding snakes.{{sfn|Deane|1833|p=61}} Snakes are worshipped as gods even today with many women pouring milk on snake pits (despite snakes' aversion for milk).{{sfn|Deane|1833|p=61}} The cobra is seen on the neck of [[Shiva]] and [[Vishnu]] is depicted often as sleeping on a seven-headed snake or within the coils of a serpent.{{sfn|Deane|1833|pp=62-64}} There are also several temples in India solely for cobras sometimes called ''Nagraj'' (King of Snakes) and it is believed that snakes are symbols of fertility. There is a Hindu festival called [[Nag Panchami]] each year on which day snakes are venerated and prayed to. See also ''[[Naga]]''.<ref>{{cite book|url=https://books.google.com/books?id=AiK2EAAAQBAJ&pg=P T782|editor=James Chambers|date=2015|title=Holiday Symbols & Customs, 5th Ed|isbn=978-0-7808-1365-6|publisher=Infobase Publishing|page=782}}</ref>

The [[Snake (zodiac)|snake]] is one of the 12 celestial animals of [[Chinese zodiac]], in the [[Chinese calendar]].<ref>{{cite web |work=timeanddate.com |title=The Chinese Calendar |url=https://www.timeanddate.com/calendar/about-chinese.html |access-date=June 1, 2017 |url-status=live |archive-url=https://web.archive.org/web/20170815132857/http s://www.timeanddate.com/calendar/about-chinese.html |archive-date=August 15, 2017}}</ref>

Many ancient Peruvian cultures worshipped nature.<ref>{{cite book |last=Benson |first=Elizabeth |title=The Mochica: A Culture of Peru |location=London |publisher=[[Thames & Hudson]] |year=1972 |isbn=978-0-500-72001-1}}</ref> They emphasized animals and often depicted snakes in their art.<ref>{{cite book |last1=Berrin |first1=Katherine |last2=Larco Museum |name-list-style=vanc |title=The Spirit of Ancient Peru: Treasures from the Museo Arqueologico Rafael Larco Herrera |location=New York |publisher=[[Thames & Hudson]] |year=1997 |isbn=978-0-500-01802-6 |title-link=Larco Museum}}</ref>

=== Religion ===
[[File:Mixco Viejo ballcourt marker.jpg|thumb|right|upright=0.85|[[Mesoamerican ballcourt|Ballcourt]] marker from the Postclassic site of [[Mixco Viejo]] in Guatemala. This sculpture depicts [[Kukulkan]], jaws agape, with the head of a human warrior emerging from his maw.<ref>{{cite book |last1=Sharer |first1=Robert J. |author-link=Robert Sharer |first2=Loa P. |last2=Traxler |name-list-style=vanc |year=2006 |title=The Ancient Maya |edition=6th (fully revised) |location=Stanford, California |publisher=[[Stanford University Press]] |isbn=978-0-8047-4817-9 |page=[https://archive.org/details/ancientmaya0006shar/page/ 619 619] |oclc=57577446 |url=https://archive.org/details/ancientmaya0006shar/page/619}}</ref>]]
{{Main|Snake worship}}
Snakes are used in [[Hinduism]] as a part of ritual worship.<ref>{{cite web |url=https://timesofindia.indiatimes.com/city/goa/hindus-uni te-to-worship-the-snake-god-today/articleshow/9474357.cms |title=Hindus unite to worship the snake god today |date=August 4, 2011 |last=Kerkar |first=Rajendra P. |work=The Times of India |access-date=March 3, 2021 |archive-date=7 May 2021 |archive-url=https://web.archive.org/web/20210507062700/http ://timesofindia.indiatimes.com/city/goa/Hindus-unite-to-wors hip-the-snake-god-today/articleshow/9474357.cms |url-status=live }}</ref> In the annual [[Nag Panchami]] festival, participants worship either live cobras or images of [[Naga]]s. Lord [[Shiva]] is depicted in most images with a snake coiled around his neck.<ref>{{cite web |url=https://www.timesnownews.com/spiritual/religion/article /what-is-the-significance-of-the-snake-around-lord-shivas-ne ck/468331 |title=What is the significance of the snake around Lord Shiva's neck? |date=August 22, 2019 |last=Iyer |first=Gayathri |website=TimesNowNews.com |access-date=March 2, 2021 |archive-date=15 April 2021 |archive-url=https://web.archive.org/web/20210415042638/http s://www.timesnownews.com/spiritual/religion/article/what-is- the-significance-of-the-snake-around-lord-shivas-neck/468331 |url-status=live }}</ref> [[Puranas|Puranic]] literature includes various stories associated with snakes, for example [[Shesha]] is said to hold all the planets of the Universe on his hoods and to constantly sing the glories of [[Vishnu]] from all his mouths. Other notable snakes in Hinduism are [[Vasuki]], [[Takshaka]], [[Karkotaka]], and [[Pingala]]. The term ''Naga'' is used to refer to entities that take the form of large snakes in Hinduism and [[Buddhism]].<ref>{{Cite web |title=naga {{!}} Hindu mythology |url=https://www.britannica.com/topic/naga-Hindu-mythology |access-date=July 1, 2022 |website=Britannica |language=en |archive-date=4 September 2022 |archive-url=https://web.archive.org/web/20220904152421/http s://www.britannica.com/topic/naga-Hindu-mythology |url-status=live }}</ref>

Snakes have been widely revered in many cultures, such as in [[ancient Greece]] where the serpent was seen as a healer.<ref>{{cite book |doi=10.1016/B978-0-12-815339-0.00017-2 |chapter=Asclepius and the Snake as Toxicological Symbols in Ancient Greece and Rome |title=Toxicology in Antiquity |date=2019 |last1=Tsoucalas |first1=Gregory |last2=Androutsos |first2=George |pages=257-265 |isbn=978-0-12-815339-0 }}</ref> [[Asclepius]] carried a serpent wound around his wand, a symbol seen today on many ambulances.<ref>{{cite web |url=https://www.mediband.com/gb/blog/medical-emergency-symb ol-origin/ |title=The Origin of the Medical Emergency Symbol |date=February 26, 2019 |website=Mediband.com |access-date=February 26, 2021 |archive-date=26 March 2023 |archive-url=https://web.archive.org/web/20230326034414/http s://www.mediband.com/gb/blog/medical-emergency-symbol-origin / |url-status=live }}</ref> In [[Judaism]], the snake of [[brass]] is also a symbol of healing, of one's life being saved from imminent death.<ref>{{bibleverse|Numbers|21:6-21:9|NAB}}</ref>

In religious terms, the snake and [[jaguar]] were arguably the most important animals in ancient [[Mesoamerica]].<ref>{{cite web |url=https://www.manzanillosun.com/the-mesoamerican-serpent/ |title=The Mesoamerican Serpent |date=2019-08-01 |last=Vickery |first=Kirby |work=Manzanillo Sun |access-date=March 3, 2021 |archive-date=20 January 2021 |archive-url=https://web.archive.org/web/20210120152448/http s://www.manzanillosun.com/the-mesoamerican-serpent/ |url-status=live }}</ref> "In states of ecstasy, lords dance a serpent dance; great descending snakes adorn and support buildings from [[Chichen Itza]] to [[Tenochtitlan]], and the [[Nahuatl]] word ''coatl'' meaning serpent or twin, forms part of primary deities such as [[Mixcoatl]], [[Quetzalcoatl]], and [[Coatlicue]]."<ref name=":4">{{cite book |last=Miller |first=Mary |title=The Gods and Symbols of Ancient Mexico and the Maya |last2=Taube |first2=Karl |date=1993 |publisher=[[Thames & Hudson]] |isbn=978-0-500-27928-1 |location=London |pages=149}}</ref> In the [[Maya calendar|Maya]] and [[Aztec calendar]]s, the fifth day sign of the 20-day cycle was "Snake".<ref>Miller & Taube (1993), p. 48.</ref>

In some parts of [[Christianity]], the redemptive work of [[Jesus|Jesus Christ]] is compared to saving one's life through beholding the [[Nehushtan]] (serpent of brass).<ref>{{bibleverse|John|3:14|NAB}}</ref> [[Snake handling in Christianity|Snake handlers]] use snakes as an integral part of church worship, to demonstrate their faith in divine protection. However, more commonly in Christianity, the serpent has been depicted as a representative of [[evil]] and sly plotting, as seen in the description in [[Book of Genesis|Genesis]] of a snake tempting [[Eve]] in the [[Garden of Eden]].<ref name=genesis/> [[Saint Patrick]] is purported to have expelled all snakes from Ireland while converting the country to Christianity in the 5th century, thus explaining the absence of snakes there.<ref>{{cite web |url=https://www.irishcentral.com/roots/saint-patrick-banish -snakes-irleand |title=Did St. Patrick really banish all the snakes from Ireland? |date=February 24, 2019 |last=Drew |first=April |website=IrishCentral.com |access-date=March 2, 2021 |archive-date=10 March 2021 |archive-url=https://web.archive.org/web/20210310204431/http s://www.irishcentral.com/roots/saint-patrick-banish-snakes-i rleand |url-status=live }}</ref>

In Christianity and Judaism, the snake makes its infamous appearance in the first book of the Bible when a serpent appears before [[Adam and Eve]] and tempts them with the [[forbidden fruit]] from the [[Tree of Knowledge of Good and Evil|Tree of Knowledge]].<ref name=genesis>{{bibleverse|Genesis|3:1|NAB}}</ref> The snake returns in the [[Book of Exodus]] when [[Moses]] turns his staff into a snake as a sign of God's power, and later when he makes the Nehushtan, a bronze snake on a pole that when looked at cured the people of bites from the snakes that plagued them in the desert. The serpent makes its final appearance symbolizing [[Satan]] in the [[Book of Revelation]]: "And he laid hold on the dragon the old serpent, which is the devil and Satan, and bound him for a thousand years."<ref>{{bibleverse|Revelation|20:2|NAB}}</ref>

In [[Neo-Paganism]] and [[Wicca]], the snake is seen as a symbol of wisdom and knowledge.<ref>{{Cite web |title=DISCUSSION ON WITCHCRAFT, WICCA NEO-PAGANISM AND AFRICAN TRADITIONS |url=https://people.ucalgary.ca/~nurelweb/papers/hayes/witch .html |access-date=2022-07-01 |website=people.ucalgary.ca |archive-date=9 June 2022 |archive-url=https://web.archive.org/web/20220609060259/http s://people.ucalgary.ca/~nurelweb/papers/hayes/witch.html |url-status=live }}</ref> Additionally, snakes are sometimes associated with [[Hecate]], the Greek goddess of [[witchcraft]].<ref>{{cite book |first=Oskar |last=Seyffert |title=A Dictionary of Classical Antiquities: Mythology, Religion, Literature and Art |url=https://archive.org/details/b3135841x/page/270/mode/2up ?view=theater |publisher=[[William Swan Sonnenschein|Swan Sonnenschein and Co]] |edition=6 |date=1901 |page=271 |access-date=January 2, 2022}}</ref>

=== Medicine ===
Several compounds from snake venoms are being researched as potential treatments or preventatives for pain, cancers, arthritis, stroke, heart disease, hemophilia, and hypertension, as well as to control bleeding (e.g., during surgery).<ref>{{cite journal |vauthors=Vyas VK, Brahmbhatt K, Bhatt H, Parmar U |title=Therapeutic potential of snake venom in cancer therapy: current perspectives |journal=Asian Pacific Journal of Tropical Biomedicine |volume=3 |issue=2 |pages=156-62 |date=February 2013 |pmid=23593597 |pmc=3627178 |doi=10.1016/S2221-1691(13)60042-8}}</ref><ref>{{cite journal |last1=Holland |first1=Jennifer S. |name-list-style=vanc |title=The Bite That Heals |journal=[[National Geographic]] |date=February 2013 |url=https://www.nationalgeographic.com/magazine/2013/02/ven om/|archive-url=https://web.archive.org/web/20180525062346/h ttps://www.nationalgeographic.com/magazine/2013/02/venom/|ar chive-date=25 May 2018}}</ref><ref>{{cite book |last1=Wilcox |first1=Christie |name-list-style=vanc |title=Venomous |date=2016 |publisher=[[Scientific American]] |isbn=978-0-374-28337-7 |url=http://christiewilcox.com/venomous.html |access-date=24 May 2018 |archive-date=24 May 2018 |archive-url=https://web.archive.org/web/20180524221949/http ://christiewilcox.com/venomous.html |url-status=live }}</ref>

== See also ==
{{div col|colwidth=30em}}
* [[Limbless vertebrates]]
* [[List of Serpentes families]]
* [[List of snakes]]
* [[Ophiology]]
* [[Snakebot]]
* [[Snake detection theory]]
* [[Spinal osteoarthropathy]] (reptile disease)
* ''[[The New Encyclopedia of Snakes]]''
* ''[[The Snakes of Europe]]''
{{div col end}}

== References ==
{{reflist}}

===Bibliography===
* {{cite book |last1=Behler |first1=John L. |last2=King |first2=F. Wayne |name-list-style=vanc |title=The Audubon Society Field Guide to Reptiles and Amphibians of North America |publisher=[[Alfred A. Knopf]] |location=New York |page=[https://archive.org/details/audubonsocietyfi00behl/pa ge/581 581] |year=1979 |isbn=978-0-394-50824-5 |url=https://archive.org/details/audubonsocietyfi00behl/page /581 }}
* [[George_Albert_Boulenger|Boulenger, G. A.]] (1913), ''[https://www.gutenberg.org/ebooks/46590 The Snakes of Europe]'', Metheun & Co. Ltd.
* {{cite book|last1=Campbell|first1=Sheldon|last2=Shaw|first2=Charles E.|title=Snakes of The American West|year=1974|publisher=[[Alfred A. Knopf]]|location=New York|isbn=978-0-394-48882-0}}
* {{cite book |last1=Cogger |first1=Harold |name-list-style=vanc |author-link=Harold Cogger |last2=Zweifel |first2=Richard |title=Reptiles & Amphibians |publisher=Weldon Owen |location=Sydney |year=1992 |isbn=978-0-8317-2786-4 |url=https://archive.org/details/reptilesamphibia00coggrich }}
* {{cite book |last=Deane |first=John |author-link=The Worship of the Serpent |title=The Worship of the Serpent |publisher=Kessinger Publishing |year=1833 |location=Whitefish, Montana |page=412 |url=http://www.sacred-texts.com/etc/wos/index.htm |isbn=978-1-56459-898-1 |access-date=2 December 2007 |archive-date=9 October 2019 |archive-url=https://web.archive.org/web/20191009000202/http s://www.sacred-texts.com/etc/wos/index.htm |url-status=live }}
* {{cite book |last1=Freiberg |first1=Marcos |last2=Walls |first2=Jerry |name-list-style=vanc |title=The World of Venomous Animals |year=1984 |publisher=TFH Publications |location=New Jersey |isbn=978-0-87666-567-1 |url=https://archive.org/details/worldofvenomousa00marc }}

== Further reading ==
{{Refbegin|30em}}
* {{cite book |last=Bullfinch |first=Thomas |name-list-style=vanc |author-link=Thomas Bullfinch |title=Bullfinch's Complete Mythology |publisher=Chancellor Press |year=2000 |location=London |page=679 |url=http://etext.library.adelaide.edu.au/b/bulfinch/thomas/ |isbn=978-0-7537-0381-6 |archive-url=https://web.archive.org/web/20090209004721/http ://etext.library.adelaide.edu.au/b/bulfinch/thomas/ |archive-date=February 9, 2009 }}
* {{cite book |last1=Capula |first1=Massimo |last2=Behler |first2=John L. |name-list-style=vanc |title=Simon & Schuster's Guide to Reptiles and Amphibians of the World |year=1989 |publisher=[[Simon & Schuster]] |location=New York |isbn=978-0-671-69098-4 |url=https://archive.org/details/simonschustersgu00capu }}
* {{cite book |last=Coborn |first=John |name-list-style=vanc |title=The Atlas of Snakes of the World |year=1991 |location=New Jersey |publisher=TFH Publications |isbn=978-0-86622-749-0}}
* {{cite book |last1=Conant |first1=Roger |last2=Collins |first2=Joseph |name-list-style=vanc |author-link=Roger Conant (herpetologist) |title=A Field Guide to Reptiles and Amphibians Eastern/Central North America |publisher=[[Houghton Mifflin Company]] |year=1991 |location=Boston |isbn=978-0-395-58389-0 |url-access=registration |url=https://archive.org/details/fieldguidetorept00cona }}
* {{cite book |last=Ditmars |first=Raymond L |author-link=Raymond Ditmars |title=Poisonous Snakes of the United States: How to Distinguish Them |publisher=E. R. Sanborn |year=1906 |location=New York |page=11}}
* {{cite book |last=Ditmars |first=Raymond L |author-link=Raymond Ditmars |title=Snakes of the World |url=https://archive.org/details/snakesofworld00ditm |url-access=registration |publisher=Macmillan |year=1931 |location=New York |page=[https://archive.org/details/snakesofworld00ditm/page/ 11 11] |isbn=978-0-02-531730-7 }}
* {{cite book |last=Ditmars |first=Raymond L |name-list-style=vanc |author-link=Raymond Ditmars |title=Reptiles of the World: The Crocodilians, Lizards, Snakes, Turtles and Tortoises of the Eastern and Western Hemispheres |publisher=Macmillan |year=1933 |location=New York |page=321}}
* {{cite book |last1=Ditmars |first1=Raymond L. |first2=W. |last2=Bridges |name-list-style=vanc |author-link=Raymond Ditmars |title=Snake-Hunters' Holiday |publisher=D. Appleton and Company |year=1935 |location=New York |page=309}}
* {{cite book |last=Ditmars |first=Raymond L |name-list-style=vanc |author-link=Raymond Ditmars |title=A Field Book of North American Snakes |publisher=Doubleday, Doran & Co |year=1939 |location=Garden City, New York |page=305}}
* {{cite book |last1=Gibbons |first1=J. Whitfield |last2=Gibbons |first2=Whit |name-list-style=vanc |title=Their Blood Runs Cold: Adventures With Reptiles and Amphibians |url=https://archive.org/details/theirbloodrunsco0000gibb |url-access=registration |publisher=[[University of Alabama Press]] |year=1983 |location=Alabama |page=[https://archive.org/details/theirbloodrunsco0000gibb/ page/164 164] |isbn=978-0-8173-0135-4 }}
* {{cite book |last=Mattison |first=Chris |name-list-style=vanc |title=The New Encyclopedia of Snakes |publisher=[[Princeton University Press]] |year=2007 |location=New Jersey |page=272 |isbn=978-0-691-13295-2}}
* {{cite book |vauthors=McDiarmid RW, Campbell JA, Toure T |year=1999 |title=Snake Species of the World: A Taxonomic and Geographic Reference |volume=1 |publisher=Herpetologists' League |page=511 |isbn=978-1-893777-00-2}}
* {{cite book |last=Mehrtens |first=John |name-list-style=vanc |title=Living Snakes of the World in Color |url=https://archive.org/details/livingsnakesofwo00mehr |url-access=registration |year=1987 |publisher=Sterling |location=New York |isbn=978-0-8069-6461-4 }}
* {{cite journal |last1=Nobrega Alves |first1=RoMulo Romeu |last2=Silva Vieira |first2=Washington Luiz |last3=Santana |first3=Gindomar Gomes |name-list-style=vanc |title=Reptiles used in traditional folk medicine: conservation implications |journal=[[Biodiversity and Conservation]] |volume=17 |issue=8 |pages=2037-2049 |year=2008 |doi=10.1007/s10531-007-9305-0 |bibcode=2008BiCon..17.2037D |s2cid=42500066}}
*{{cite book 
|last1=O'Shea|first1=Mark
|title=Snakes of the World: a Guide to Every Family
|date=2023 
|publisher=Princeton University Press 
|location=Princeton, New Jersey
|isbn=978-0-691-24066-4}}
* {{cite book |first=Romulus |last=Whitaker |name-list-style=vanc |title=nmmai cuttriyullll paampukll (Snakes around us, Tamil) |publisher=National Book Trust |year=1996 |isbn=978-81-237-1905-4 |author-link=Romulus Whitaker}}
* {{cite book |last=Rosenfeld |first=Arthur |name-list-style=vanc |title=Exotic Pets |url=https://archive.org/details/exoticpets0000rose |url-access=limited |publisher=[[Simon & Schuster]] |location=New York |year=1989 |page=[https://archive.org/details/exoticpets0000rose/page/2 93 293] |isbn=978-0-671-47654-0 }}
* {{cite book |last1=Spawls |first1=Steven |last2=Branch |first2=Bill |name-list-style=vanc |year=1995 |title=The Dangerous Snakes of Africa |publisher=Ralph Curtis Publishing |location=Sanibel Island, Florida |page=192 |isbn=978-0-88359-029-4}}
{{Refend}}

== External links ==
{{wiktionary}}
{{wikiquote}}
{{commons and category|Serpentes}}
{{Americana Poster|Serpents}}
* {{cite web |url=https://www.biodiversitylibrary.org/name/Serpentes |title=Bibliography for "Serpentes" |publisher=Biodiversity Heritage Library}}
* {{ITIS |id=174118 |taxon=Serpentes}}
* {{cite web |url=http://enature.com/fieldguides/view_default.asp?curGrou pID=7&shapeID=1060 |title=US Snakes |publisher=eNature |archive-url=https://web.archive.org/web/20080315050142/http ://www.enature.com/fieldguides/view_default.asp?curGroupID=7 &shapeID=1060 |archive-date=2008-03-15}}
* {{cite web |url=http://www.naturemagics.com/stock-photo/thumbnails.php? album=7 |title=Snakes of the Indian Subcontinent |publisher=Naturemagics Kerala Photo Gallery |access-date=8 January 2007 |archive-date=21 March 2009 |archive-url=https://web.archive.org/web/20090321024830/http ://naturemagics.com/stock-photo/thumbnails.php?album=7 }}
* {{cite web |url=http://artedi.nrm.se/nrmherps/qbrowse.php?FormData=scie ntificName |title=Herpetology Database |publisher=Swedish Museum of Natural History}}
* [https://web.archive.org/web/20101203161539/http://www.bbc.c o.uk/nature/life/Snake BBC Nature:] Snake news, and video clips from BBC programmes past and present.
* [https://snakesarelong.blogspot.com/2013/05/basics-of-snake- taxonomy.html Basics of snake taxonomy] at Life is Short but Snakes are Long

{{Snake families}}
{{Reptiles in culture}}
{{Portal bar|Snakes|Reptiles|Animals}}

{{Taxonbar|from=Q25537662}}
{{Authority control}}

[[Category:Snakes| ]]
[[Category:Cenomanian first appearances]]
[[Category:Animal taxa named by Carl Linnaeus]]
[[Category:Extant Cenomanian first appearances]]
[[Category:Ophidia]]

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