Snake

What is a snake?	A snake is a long, legless reptile that can be found on every continent except Antarctica.
How many species?	There are over 3,400 species of snakes in the world.
Where do they live?	Snakes live in forests, deserts, grasslands, and even underwater in some species.
Interesting fact	Some snakes can fly glide through the air using their bodies.

Snakes are long, limbless reptiles that belong to the suborder Serpentes. They are ectothermic, meaning they rely on external sources to regulate their body temperature, and they are covered in overlapping scales. One interesting feature of many snakes is their flexible skulls, which allow them to swallow prey much larger than their own heads. To fit their narrow bodies, snakes have their internal organs arranged one in front of the other, and most have only one functional lung.

Snakes live on every continent except Antarctica and can be found in many different habitats, from forests to deserts. There are around thirty families of snakes, with over 4,170 species. They vary greatly in size, from the tiny Barbados threadsnake, which is about 10.4 cm long, to the enormous reticulated python, which can reach nearly 7 meters. Scientists believe snakes evolved from lizards, possibly during the Jurassic period, around 143 to 167 million years ago.

Most snakes are not venomous. Those that do have venom use it mainly to catch their prey, though some venoms can be dangerous to humans. Nonvenomous snakes typically catch their prey by swallowing it whole or by using constriction to hold it in place.

Etymology

The English word snake comes from Old English snaca, which is related to words meaning "to crawl or creep." This idea connects to words in other languages, like the Sanskrit word for snake. Over time, the word snake became the common term, while older words like adder changed meaning. The word serpent also comes from a similar root meaning "to creep," linking back to ancient languages.

Taxonomy

Legless lizards

Main article: Legless lizard

While snakes are limbless reptiles, there are other lizards that have also lost their limbs. These lizards look similar to snakes but are not the same. Examples include glass snakes and amphisbaenians.

Evolution

The fossil record of snakes is not very complete because their small, fragile skeletons do not fossilize easily. The earliest known snake fossils come from the Cretaceous period, about 112 to 94 million years ago. These early snakes often still had hind limbs.

Scientists believe snakes evolved from lizards. Some primitive snakes, like pythons and boas, have tiny hind limbs, showing their lizard ancestors had legs. Over time, snakes lost their limbs, possibly as they adapted to burrowing or swimming.

Fossils

Fossil evidence suggests snakes may have evolved from burrowing lizards during the Cretaceous Period. An early fossil snake relative, Najash rionegrina, was a two-legged burrowing animal. Another important fossil is Tetrapodophis amplectus, a 113-million-year-old fossil that looks like a snake but has four legs. Scientists are still studying whether it was a true snake or another type of lizard.

Genetic basis of snake evolution

Main article: Limb development

Studies show that limb loss in snakes is linked to DNA mutations in a region of the sonic hedgehog gene, which is important for limb development. More advanced snakes have no traces of limbs, but some, like pythons and boas, still have small, vestigial hind limbs. Even python embryos start with fully developed hind limb buds, but these stop developing because of the DNA mutations.

Family	Taxon author	Genera	Species	Common name	Geographic range
Infraorder Alethinophidia 25 families
Acrochordidae	Bonaparte, 1831	1	3	Wart snakes	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	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	Günther, 1858	12	72	Burrowing asps	Africa and the Middle East
Boidae	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 Moluccas and New Guinea through to Melanesia and Samoa.
Bolyeriidae	Hoffstetter, 1946	2	2	Splitjaw snakes	Mauritius.
Colubridae	Oppel, 1811	258	2055	Typical snakes	Widespread on all continents, except Antarctica.
Cyclocoridae	Weinell & Brown, 2017	5	8	Cyclocorids	The Philippines
Cylindrophiidae	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 off the southwestern coast of New Guinea. Also found in southern China (Fujian, Hong Kong and on Hainan Island) and in Laos.
Elapidae	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.
Homalopsidae	Bonaparte, 1845	28	53	Homalopsids	Southeastern Asia and northern Australia.
Lamprophiidae	Fitzinger, 1843	16	89	Lamprophiids (formerly included Atracaspididae, Psammophiidae, and several other families)	Africa (including the Seychelles)
Loxocemidae	Cope, 1861	1	1	Mexican burrowing snake	Along the Pacific versant from Mexico south to Costa Rica.
Micrelapidae	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	Bourgeois, 1968	8	55	Psammophiids	Africa (including Madagascar), Asia and southern Europe
Pseudaspididae	Cope, 1893	2	2	Pseudaspidids	Subsaharan Africa
Pseudoxyrhophiidae	Dowling, 1975	22	89	Pseudoxyrhophiids	Mostly Madagascar and the Comoros; 5 species in subsaharan Africa, 1 in Socotra
Pythonidae	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	Brongersma, 1951	2	34	Dwarf boas	West Indies; also Panama and northwestern South America, as well as in northwestern and southeastern Brazil.
Uropeltidae	Müller, 1832	8	55	Shield-tailed snakes	Southern India and Sri Lanka.
Viperidae	Oppel, 1811	35	341	Vipers	The Americas, Africa, and Eurasia east to Wallace's Line.
Xenodermidae	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	Bonaparte, 1845	1	2	Sunbeam snakes	Southeast 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.
Xenophidiidae	Wallach & Günther, 1998	1	2	Spine-jawed snakes	Borneo and peninsular Malaysia.

Family	Taxon author	Genera	Species	Common name	Geographic range
Infraorder Scolecophidia 5 families
Anomalepidae	Taylor, 1939	4	18	Primitive blind snakes	From southern Central America to northwestern South America. Disjunct populations in northeastern and southeastern South America.
Gerrhopilidae	Vidal, Wynn, Donnellan and Hedges 2010	2	18	Indo-Malayan blindsnakes	Southern and southeastern Asia, including Sri Lanka, the Philippines, and New Guinea.
Leptotyphlopidae	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	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.

Distribution

Approximate world distribution of snakes

There are about 3,900 species of snakes, found nearly everywhere except Antarctica. They live as far north as the Arctic Circle in Scandinavia and as far south as Australia. Snakes can be found on land, in the sea, and even as high as 16,000 feet in the Himalayan Mountains of Asia.

Some islands, like Ireland, Iceland, and New Zealand, don’t have snakes, though New Zealand’s northern waters are sometimes visited by the yellow-bellied sea snake and the banded sea krait.

Biology

Snakes are long, limbless reptiles known for their ability to swallow prey much larger than their heads. They are covered in overlapping scales and are ectothermic, meaning they rely on external sources to regulate their body temperature.

Snakes have highly specialized sensory systems. Many, especially pit vipers, possess infrared-sensitive receptors called pits that help them detect temperature changes and track prey. They also rely on their forked tongues to gather scent particles, which are analyzed in a special organ in their mouths to locate food or predators. Most snakes can also sense vibrations, allowing them to detect sounds in their environment. Vision varies among species, with some having excellent eyesight and others seeing only light and dark, but most can track movement well.

The skin of a snake is covered in dry, smooth scales that protect them and reduce friction as they move. These scales are made of keratin and are shed periodically in a process called molting, where the snake sheds its entire outer layer of skin at once. Snakes have flexible skulls with more joints than lizards, which allows them to swallow large prey. Their skeletons consist mainly of a skull, hyoid bone, vertebral column, and ribs, with some retaining small remnants of hind limbs. Inside, snakes have a three-chambered heart and a single functional lung, adapting them well for their long, slender bodies. Some snakes, like cobras and vipers, use venom delivered through fangs to catch prey or defend themselves.

Behavior and life history

Snakes have special ways to survive and find food. In cold places, snakes enter a resting state called brumation. During brumation, snakes stay awake but do not move much. They rest in places like burrows or under rocks.

All snakes eat meat and hunt small animals such as lizards, frogs, birds, and even other snakes. They are ambush predators, meaning they wait for the right moment to catch their food. Snakes swallow their prey whole because they cannot bite or tear food into pieces. Their jaws are very flexible, allowing them to open wide enough to eat animals larger than their own heads. Some snakes use venom to kill their prey before eating, while others wrap around their prey to hold it tight. After eating, snakes rest to digest their food, which can take a long time, especially after eating large meals.

Interactions with humans

Snakes usually avoid humans and won't attack unless they feel threatened or hurt. Most snakes, especially those that aren't venomous, aren't dangerous to people. A bite from a non-venomous snake might hurt a little but is rarely serious. Venomous snakes are more dangerous, and their bites can be very serious.

In some places, people perform shows with snakes, called snake charming. These shows are becoming less common due to laws protecting animals and new forms of entertainment. Some people catch snakes to remove venom for making medicine, then let the snakes go. In many cultures, eating snake meat is popular, and snakes are also kept as pets in some countries. Snakes have appeared in stories and symbols for thousands of years, representing different ideas in various cultures and religions.