Snakes are limbless reptiles of the squamate suborder Serpentes. Closely related to lizards and the tuatara, snakes are ectothermic, amniote, air-breathing vertebrates with an elongated rope-like body covered by overlapping scales, and they move around using undulatory, rectilinear, concertina, sidewinding or slide-pushing locomotion, with some arboreal species even capable of short-ranged gliding flight by flaring out the ribs to flatten and widen the body for aerodynamic lift. Snakes have skulls with significantly fewer sutures and more hypermobile articulations (i.e. cranial kinesis) than their lizard relatives, enabling them to greatly widen the mouth and swallow prey much larger than their heads. 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. Despite being tetrapods from a cladistic prospective, snakes lack limbs completely, although pythons and boids retain a vestigial pelvic girdle. Some lizards have also independently evolved a snake-like elongated body without limbs or with greatly reduced limbs at least twenty-five times via convergent evolution, leading to many lineages of legless lizards, who have eyelids, external ears and a fleshy non-forked tongue that snakes lack, although this rule is not universal.
Snakes are mostly terrestrial with a cosmopolitan distribution, and extant species are found on every continent except Antarctica, and on most islands — exceptions include Ireland, Iceland, Greenland and the islands of New Zealand, as well as many small islands of the Atlantic and Central Pacific oceans. Additionally, secondarily aquatic groups such as the sea snakes are widespread throughout the Indo-Pacific regions, while water snakes are found worldwide. Around thirty families are currently recognized, comprising about 520 genera and about more than 4,170 species. They range in size from the tiny, Barbados threadsnake to the reticulated python up to in length. The fossil species Titanoboa cerrejonensis was long. 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 Ma ago. The diversity of modern snakes appeared during the Paleocene epoch ( 66 to 56 Ma ago, after the Cretaceous–Paleogene extinction event). The oldest preserved descriptions of snakes can be found in the Brooklyn Medical Papyrus.
Most species of snake are non-venomous, and venomous snake species use their venom primarily to paralyze and kill prey rather than for self-defense. Snake venom is delivered during biting via hollow/grooved fangs and contains a wide variety of toxins including neurotoxins, hemotoxins, cardiotoxins and myotoxins, and some are potent enough to cause severe injury or death to humans with just one snakebite. Non-venomous snakes typically subdue prey by constriction before either swallow the prey alive or kill it by strangulation before swallowing whole. In captivity, snakes are typically fed dead prey because live foods such as rodents may fight and injure snakes during feeding.Enviroliteracy Team, "Can You Feed Pet Snakes Live Animals?", The Environmental Literacy Council, 4 April 2025Maria Zayas, DVM, "What Do Pet Snakes Eat?", PetMD, 6 January 2023
Etymology The English word snake comes from Old English , itself from Proto-Germanic (cf. Swedish 'grass snake'), from Proto-Indo-European root 'to crawl to creep', which also gave sneak as well as Sanskrit 'snake'.Proto-IE: , Meaning: snake, Old Indian: nāgá- m. 'snake', Germanic: m., m., f.; vb., Russ. meaning: (), References: WP () II 697 f. The word ousted adder, as adder went on to narrow in meaning, though in Old English was the general word for snake. The other term, serpent, is from French, ultimately from Indo-European 'to creep', which also gave Ancient Greek () 'I crawl' and Sanskrit 'snake'.
Taxonomy
All modern snakes are grouped within the suborder Serpentes in Linnean taxonomy, part of the order Squamata, though their precise placement within squamates remains controversial.
The two infraorders of Serpentes are Alethinophidia and Scolecophidia. This separation is based on morphological characteristics and mitochondrial DNA sequence similarity. Alethinophidia is sometimes split into Henophidia and Caenophidia, with the latter consisting of "colubroid" snakes (colubrids, vipers, elapids, hydrophiids, and atractaspids) and acrochordids, while the other alethinophidian families comprise Henophidia. 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.
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.
Families Infraorder Alethinophidia 25 familiesFamilyTaxon authorGeneraSpeciesCommon nameGeographic rangeMcDiarmid RW, Campbell JA, Touré T. 1999. Snake Species of the World: A Taxonomic and Geographic Reference, vol. 1. Herpetologists' League. 511 pp. (series). (volume).AcrochordidaeBonaparte, 183113Wart snakesWestern 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.AniliidaeStejneger, 190711False coral snakeTropical South America.AnomochilidaeCundall, Wallach, 199313Dwarf pipe snakesWest Malaysia and on the Indonesian island of Sumatra.AtractaspididaeGünther, 18581272Burrowing aspsAfrica and the Middle EastBoidaeGray, 18251461BoasNorthern, 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 Moluccas and New Guinea through to Melanesia and Samoa.BolyeriidaeHoffstetter, 194622Splitjaw snakesMauritius.ColubridaeOppel, 18112582055Typical snakesWidespread on all continents, except Antarctica.CyclocoridaeWeinell & Brown, 201758CyclocoridsThe PhilippinesCylindrophiidaeFitzinger, 1843114Asian pipe snakesSri Lanka east through Myanmar, Thailand, Cambodia, Vietnam and the Malay Archipelago to as far east as Aru Islands off the southwestern coast of New Guinea. Also found in southern China (Fujian, Hong Kong and on Hainan Island) and in Laos.ElapidaeBoie, 182755389ElapidsOn land, worldwide in tropical and subtropical regions, except in Europe. Sea snakes occur in the Indian Ocean and the Pacific.HomalopsidaeBonaparte, 18452853HomalopsidsSoutheastern Asia and northern Australia.LamprophiidaeFitzinger, 18431689Lamprophiids (formerly included Atracaspididae, Psammophiidae, and several other families)Africa (including the Seychelles)LoxocemidaeCope, 186111Mexican burrowing snakeAlong the Pacific versant from Mexico south to Costa Rica.MicrelapidaeDas et al., 202314Two-headed snakesEastern Africa and the LevantPareidaeRomer, 1956320Snail-eating snakesSoutheast Asia and islands on the Sunda Shelf (Sumatra, Borneo, Java, and their surrounding smaller islands).ProsymnidaeKelly, Barker, Villet & Broadley, 2009116Shovel-snout snakesSubsaharan AfricaPsammodynastidaeDas et al., 202412Mock vipersTropical AsiaPsammophiidaeBourgeois, 1968855PsammophiidsAfrica (including Madagascar), Asia and southern EuropePseudaspididaeCope, 189322 PseudaspididsSubsaharan AfricaPseudoxyrhophiidaeDowling, 19752289 PseudoxyrhophiidsMostly Madagascar and the Comoros; 5 species in subsaharan Africa, 1 in SocotraPythonidaeFitzinger, 1826840PythonsSubsaharan Africa, India, Myanmar, southern China, Southeast Asia and from the Philippines southeast through Indonesia to New Guinea and Australia.TropidophiidaeBrongersma, 1951234Dwarf boasWest Indies; also Panama and northwestern South America, as well as in northwestern and southeastern Brazil.UropeltidaeMüller, 1832855Shield-tailed snakesSouthern India and Sri Lanka.ViperidaeOppel, 181135341VipersThe Americas, Africa, and Eurasia east to Wallace's Line.XenodermidaeCope, 1900618Dragon and odd-scaled snakesEast Asia, Southern and southeastern Asia, and islands on the Sunda Shelf (Sumatra, Borneo, Java, and their surrounding smaller islands).XenopeltidaeBonaparte, 184512Sunbeam snakesSoutheast Asia from the 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.XenophidiidaeWallach & Günther, 199812Spine-jawed snakesBorneo and peninsular Malaysia.
Infraorder Scolecophidia 5 familiesFamilyTaxon authorGeneraSpeciesCommon nameGeographic rangeAnomalepidaeTaylor, 1939418Primitive blind snakesFrom southern Central America to northwestern South America. Disjunct populations in northeastern and southeastern South America.GerrhopilidaeVidal, Wynn, Donnellan and Hedges 2010218Indo-Malayan blindsnakesSouthern and southeastern Asia, including Sri Lanka, the Philippines, and New Guinea.LeptotyphlopidaeStejneger, 189213139Slender blind snakesAfrica, 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.TyphlopidaeMerrem, 182018266Typical blind snakesMost tropical and many subtropical regions around the world, particularly in Africa, Madagascar, Asia, islands in the Pacific, tropical America and in southeastern Europe.XenotyphlopidaeVidal, Vences, Branch and Hedges 201011Round-nosed blindsnakeNorthern Madagascar.
Legless lizards
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 glass snakes (including the slowworm), and amphisbaenians.
Evolution
The fossil record of snakes is relatively poor because snake skeletons are typically small and fragile making fossilization uncommon. Fossils readily identifiable as snakes (though often retaining hind limbs) first appear in the fossil record during the Cretaceous period. The earliest known true snake fossils (members of the crown group Serpentes) come from the marine simoliophiids, the oldest of which is the Late Cretaceous (Cenomanian age) Haasiophis terrasanctus from the West Bank, dated to between 112 and 94 million years old.
Based on genomic analysis it is certain that snakes descend from lizards. This conclusion is also supported by comparative anatomy, and the fossil record.
Pythons and boas—primitive groups among modern snakes—have vestigial hind limbs: tiny, clawed digits known as anal spurs, which are used to grasp during mating. The families Leptotyphlopidae and Typhlopidae also possess remnants of the pelvic girdle, appearing as horny projections when visible.