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This article is about the animal. For other uses, see Snake (disambiguation).
Temporal range:
Late CretaceousHolocene,1 94–0Ma
Coast Garter Snake.jpg
Western terrestrial garter snake, a species from western North America
Scientific classification e
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Order: Squamata
Clade: Ophidia
Suborder: Serpentes
Linnaeus, 1758
World distribution of snakes.svg
Approximate world distribution of snakes, all species


Living snakes are found on every continent except Antarctica, and on most smaller land masses — exceptions include some large islands, such as Ireland and New Zealand, and many small islands of the Atlantic and central Pacific.3 Additionally, sea snakes are widespread throughout the Indian and Pacific Oceans. More than 20 families are currently recognized, comprising about 500 genera and about 3,400 species.45 They range in size from the tiny, 10 cm-long thread snake to the Reticulated python of up to 6.95 meters (22.8 ft) in length.6 The fossil species Titanoboa cerrejonensis was 13 meters (43 ft) long.7 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.8 The diversity of modern snakes appeared during the Paleocene period (c 66 to 56 Ma ago). The oldest preserved descriptions of snakes can be found in the Brooklyn Papyrus.



The English word snake comes from Old English snaca, itself from Proto-Germanic *snak-an- (cf. Germanic Schnake "ring snake", Swedish snok "grass snake"), from Proto-Indo-European root *(s)nēg-o- "to crawl", "to creep", which also gave sneak as well as Sanskrit nāgá "snake".9 The word ousted adder, as adder went on to narrow in meaning, though in Old English næddre was the general word for snake.10 The other term, serpent, is from French, ultimately from Indo-European *serp- (to creep),11 which also gave Ancient Greek hérpō (ἕρπω) "I crawl".


A phylogenetic overview of the extant groups
Modern snakes







Core Alethinophidia






















Note: the tree only indicates relationships, not evolutionary branching times.12

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.13 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,1 dated to between 112 and 94 million years old.14

Based on comparative anatomy, there is consensus that snakes descended from lizards.15:1116 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.15:1117 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 Hox genes, 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, 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.

Modern snakes greatly diversified during the Paleocene. This occurred alongside the adaptive radiation of mammals, following the extinction of (non-avian) dinosaurs. The colubrids, one of the more common snake groups, became particularly diverse due to preying on rodents, an especially successful mammal group.


The origin of snakes remains an unresolved issue. There are two main hypotheses competing for acceptance.

Burrowing lizard hypothesis

There is fossil evidence to suggest that snakes may have evolved from burrowing lizards, such as the varanids (or a similar group) during the Cretaceous Period.18 An early fossil snake relative, Najash rionegrina, was a two-legged burrowing animal with a sacrum, and was fully terrestrial.19 One extant analog of these putative ancestors is the earless monitor Lanthanotus of Borneo (though it also is semiaquatic).20 Subterranean species evolved bodies streamlined for burrowing, and eventually lost their limbs.20 According to this hypothesis, features such as the transparent, fused eyelids (brille) and loss of external ears evolved to cope with fossorial difficulties, such as scratched corneas and dirt in the ears.1820 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.17

Fossil of Archaeophis proavus.
Aquatic mosasaur hypothesis

An alternative hypothesis, based on morphology, suggests the ancestors of snakes were related to mosasaurs—extinct aquatic reptiles from the Cretaceous—which in turn are thought to have derived from varanid lizards.16 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 lead to an animal similar to today's sea snakes. 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 cladistical correlation, although some of these features are shared with varanids.

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.


Approximate world distribution of snakes.

There are over 2,900 species of snakes ranging as far northward as the Arctic Circle in Scandinavia and southward through Australia.16 Snakes can be found on every continent except Antarctica, in the sea, and as high as 16,000 feet (4,900 m) in the Himalayan Mountains of Asia.1621:143 There are numerous islands from which snakes are absent, such as Ireland, Iceland, and New Zealand321 (although New Zealand's waters are infrequently visited by the yellow-bellied sea snake and the banded sea krait).22


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.4

The two infraorders of Serpentes are: Alethinophidia and Scolecophidia.4 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.23 While not extant today, the Madtsoiidae, a family of giant, primitive, python-like snakes, was around until 50,000 years ago in Australia, represented by genera such as Wonambi.

There are numerous debates in the systematics within the group. For instance, many sources classify Boidae and Pythonidae as one family, while some keep the Elapidae and Hydrophiidae (sea snakes) separate for practical reasons despite their extremely close relation.

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.12


Infraorder Alethinophidia 15 families
Family4 Taxon author4 Genera4 Species4 Common name Geographic range24
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 2 Dwarf pipe snakes West Malaysia and on the Indonesian island of Sumatra.
Atractaspididae Günther, 1858 12 64 Burrowing asps Africa and the Middle East.152526
Boidae Gray, 1825 8 43 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 3045 19385 Typical snakes Widespread on all continents, except Antarctica.27
Cylindrophiidae Fitzinger, 1843 1 8 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 61 235 Elapids On land, worldwide in tropical and subtropical regions, except in Europe. Sea snakes occur in the Indian Ocean and the Pacific.28
Loxocemidae Cope, 1861 1 1 Mexican burrowing snake Along the Pacific versant from Mexico south to Costa Rica.
Pythonidae Fitzinger, 1826 8 26 Pythons Subsaharan Africa, India, Myanmar, southern China, Southeast Asia and from the Philippines southeast through Indonesia to New Guinea and Australia.
Tropidophiidae Brongersma, 1951 4 22 Dwarf boas From southern Mexico and Central America, south to northwestern South America in Colombia, (Amazonian) Ecuador and Peru, as well as in northwestern and southeastern Brazil. Also found in the West Indies.
Uropeltidae Müller, 1832 8 47 Shield-tailed snakes Southern India and Sri Lanka.
Viperidae Oppel, 1811 32 224 Vipers The Americas, Africa and Eurasia.
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.

Infraorder Scolecophidia 3 families
Family4 Taxon author4 Genera4 Species4 Common name Geographic range24
Anomalepidae Taylor, 1939 4 15 Primitive blind snakes From southern Central America to northwestern South America. Disjunct populations in northeastern and southeastern South America.
Leptotyphlopidae Stejneger, 1892 2 87 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 6 203 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.

Legless lizards

Main article: Legless lizard

While snakes are limbless reptiles which evolved from (and are grouped within) lizards, there are may other species of lizards which have lost their limbs independently and superficially look similar to snakes. These include the slow worm and glass snake.


An adult Barbados threadsnake, Leptotyphlops carlae, on an American quarter dollar.


The now extinct Titanoboa cerrejonensis snakes found were 12.8–13 m (42–43 ft) in length.7 By comparison, the largest extant snakes are the reticulated python, the longest recorded specimen measured about 6.95 m (22.8 ft) long,6 and the anaconda, which measures about 5.21 m (17.1 ft) long29 and is considered the heaviest snake on Earth.

At the other end of the scale, the smallest extant snake is Leptotyphlops carlae, with a length of about 10 cm (3.9 in).30 Most snakes are fairly small animals, approximately 1 m (3.3 ft) in length.31


Snakes use smell to track their prey. They smell by using their forked tongues to collect airborne particles, then passing them to the vomeronasal organ or Jacobson's organ in the mouth for examination.32 The fork in the tongue gives snakes a sort of directional sense of smell and taste simultaneously.32 They keep their tongues constantly in motion, sampling particles from the air, ground, and water, analyzing the chemicals found, and determining the presence of prey or predators in the local environment. In water-dwelling snakes, such as the Anaconda, the tongue functions efficiently under water.32
Snake vision varies greatly, from only being able to distinguish light from dark to keen eyesight, but the main trend is that their vision is adequate although not sharp, and allows them to track movements.33 Generally, vision is best in arboreal snakes and weakest in burrowing snakes. Some snakes, such as the Asian vine snake (genus Ahaetulla), have binocular vision, with both eyes capable of focusing on the same point. Most snakes focus by moving the lens back and forth in relation to the retina, while in the other amniote groups, the lens is stretched. Many nocturnal snakes have slit pupils while diurnal snakes have round pupils.
Thermographic image of a snake eating a mouse.
Infrared sensitivity
Pit vipers, pythons, and some boas have infrared-sensitive receptors in deep grooves on the snout, which allow them to "see" the radiated heat of warm-blooded prey mammals. In pit vipers the grooves are located between the nostril and the eye, in a large "pit" on each side of the head. Other infrared-sensitive snakes have multiple, smaller labial pits lining the upper lip, just below the nostrils.32
Vibration sensitivity
The part of the body in direct contact with the ground is very sensitive to vibration; thus, a snake can sense other animals approaching by detecting faint vibrations in the air and on the ground.32


Main article: Snake scales


The shedding of scales is called ecdysis (or in normal usage, molting or sloughing). In the case of snakes, the complete outer layer of skin is shed in one layer.34 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.35


Eye scales visible during the molt of a Diamond Python.

Snakes' eyes are covered by their clear scales (the brille) rather than movable eyelids. Their eyes are always open, and for sleeping, the retina can be closed or the face buried among the folds of the body.



A snake shedding its skin.


Rat snake (Pantherophis obsoletus) showing cloudy eye as molting begins. Missouri Ozarks.

An older snake may shed its skin only once or twice a year. But a younger snake, still growing, may shed up to four times a year.37 The discarded skin gives a perfect imprint of the scale pattern, and it is usually possible to identify the snake if the discarded skin is reasonably intact.35 This periodic renewal has led to the snake being a symbol of healing and medicine, as pictured in the Rod of Asclepius.38


When compared, the skeletons of snakes are radically different from those of most other reptiles (such as the turtle, right), being made up almost entirely of an extended ribcage.


The skull of the snake consists of a solid and complete neurocranium, to which many of the other bones are only loosely attached, particularly the highly mobile jaw bones, which facilitate manipulation and ingestion of large prey items. The left and right sides of the lower jaw are joined only by a flexible ligament at the anterior tips, allowing them to separate widely, while the posterior end of the lower jaw bones articulate with a quadrate bone, allowing further mobility. The bones of the mandible and quadrate bones can also pick up ground borne vibrations.39 Because the sides of the jaw can move independently of one another, snakes resting their jaws on a surface have sensitive stereo hearing which can detect 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 ossicle mechanism of impedance matching used in other vertebrates to receive vibrations from the air.4041


The vertebral column consists of anywhere between 200 to 400 (or more) vertebrae. Tail vertebrae are comparatively few in number (often less than 20% of the total) and lack ribs, while body vertebrae each have two ribs articulating with them. The vertebrae have projections that allow for strong muscle attachment enabling locomotion without limbs.

Autotomy of the tail, a feature found in some lizards is absent in most snakes.42 Caudal autotomy in snakes is rare and is intervertebral, unlike that in lizards, which is intravertebral—that is, the break happens along a predefined fracture plane present on a vertebra.4344

In some snakes, most notably boas and pythons, there are vestiges of the hindlimbs in the form of a pair of pelvic spurs. 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.

Internal organs



The vestigial left lung is often small or sometimes even absent, as snakes' tubular bodies require all of their organs to be long and thin.45 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.45 This 'saccular lung' is used for hydrostatic purposes to adjust buoyancy in some aquatic snakes and its function remains unknown in terrestrial species.45 Many organs that are paired, such as kidneys or reproductive organs, are staggered within the body, with one located ahead of the other.45

Snakes have no lymph nodes.45


Snakes are polyphyodonts with teeth that are continuously replaced.46


Milk snakes are often mistaken for coral snakes whose venom is deadly to humans.

Cobras, vipers, and closely related species use venom to immobilize or kill their prey. The venom is modified saliva, delivered through fangs.15:243 The fangs of 'advanced' venomous snakes like viperids and elapids are hollow to inject venom more effectively, while the fangs of rear-fanged snakes such as the boomslang merely have a groove on the posterior edge to channel venom into the wound. Snake venoms are often prey specific—their role in self-defense is secondary.15:243

Venom, like all salivary secretions, is a predigestant that initiates the breakdown of food into soluble compounds, facilitating proper digestion. Even nonvenomous snake bites (like any animal bite) will cause tissue damage.15:209

Certain birds, mammals, and other snakes (such as kingsnakes) that prey on venomous snakes have developed resistance and even immunity to certain venoms.15:243 Venomous snakes include three families of snakes, and do not constitute a formal classification group used in taxonomy.

The term "poisonous snake" is mostly incorrect. Poison is inhaled or ingested, whereas venom is injected.47 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 population of garter snakes in Oregon retains enough toxin in their liver from the newts they eat to be effectively poisonous to small local predators (such as crows and foxes).48

Snake venoms are complex mixtures of proteins, and are stored in venom glands at the back of the head.48 In all venomous snakes, these glands open through ducts into grooved or hollow teeth in the upper jaw.15:24347 These proteins can potentially be a mix of neurotoxins (which attack the nervous system), hemotoxins (which attack the circulatory system), cytotoxins, bungarotoxins and many other toxins that affect the body in different ways.47 Almost all snake venom contains hyaluronidase, an enzyme that ensures rapid diffusion of the venom.15:243

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.47 Some snakes that use neurotoxins (such as the mangrove snake) have fangs in the back of their mouths, with the fangs curled backwards.49 This makes it difficult both for the snake to use its venom and for scientists to milk them.47 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.15:242

It has recently been suggested that all snakes may be venomous to a certain degree, with harmless snakes having weak venom and no fangs.50 Most snakes currently labelled "nonvenomous" would still be considered harmless according to this theory, as they either lack a venom delivery method or are incapable of delivering enough to endanger a human. This theory postulates that snakes may have evolved from a common lizard ancestor that was venomous—and that venomous lizards like the gila monster, beaded lizard, monitor lizards, and the now-extinct mosasaurs may also have derived from it. They share this venom clade with various other saurian species.

Venomous snakes are classified in two taxonomic families:

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


Although a wide range of reproductive modes are used by snakes, all snakes employ internal fertilization. This is accomplished by means of paired, forked hemipenes, which are stored, inverted, in the male's tail.51 The hemipenes are often grooved, hooked, or spined in order to grip the walls of the female's cloaca.51

Most species of snakes lay eggs, but most snakes abandon the eggs shortly after laying. However, a few species (such as the king cobra) actually construct nests and stay in the vicinity of the hatchlings after incubation.51 Most pythons coil around their egg-clutches and remain with them until they hatch.52 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.52

Some species of snake are ovoviviparous and retain the eggs within their bodies until they are almost ready to hatch.5354 Recently, it has been confirmed that several species of snake are fully viviparous, such as the boa constrictor and green anaconda, nourishing their young through a placenta as well as a yolk sac, which is highly unusual among reptiles, or anything else outside of requiem sharks or placental mammals.5354 Retention of eggs and live birth are most often associated with colder environments.5154


Winter dormancy

In regions where winters are colder than snakes can tolerate while remaining active, local species will brumate. Unlike hibernation, in which mammals are actually asleep, brumating reptiles are awake but inactive. Individual snakes may brumate in burrows, under rock piles, or inside fallen trees, or snakes may aggregate in large numbers at hibernacula.

Feeding and diet

Snake eating a rodent.
Green Tree Snake - Dendrelaphis punctulata - eating White-lipped Tree Frog near Cooktown, Queensland, Australia.
Carpet python constricting and consuming a chicken.

All snakes are strictly carnivorous, eating small animals including lizards, frogs, other snakes, small mammals, birds, eggs, fish, snails or insects.15[1]1655 Because snakes cannot bite or tear their food to pieces, they must swallow prey whole. The body size of a snake has a major influence on its eating habits. 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.

The snake's jaw is a complex structure. Contrary to the popular belief that snakes can dislocate their jaws, snakes have a very flexible lower jaw, the two halves of which are not rigidly attached, and numerous other joints in their skull (see snake skull), allowing them to open their mouths wide enough to swallow their prey whole, even if it is larger in diameter than the snake itself.55 For example, the African egg-eating snake has flexible jaws adapted for eating eggs much larger than the diameter of its head.15:81 This snake has no teeth, but does have bony protrusions on the inside edge of its spine, which it uses to break shells when it eats eggs.15:81

While the majority of snakes eat a variety of prey animals, there is some specialization by some species. King cobras and the Australian bandy-bandy consume other snakes. Pareas iwesakii and other snail-eating colubrids of subfamily Pareatinae have more teeth on the right side of their mouths than on the left, as the shells of their prey usually spiral clockwise15:18456

Some snakes have a venomous bite, which they use to kill their prey before eating it.5557 Other snakes kill their prey by constriction.55 Still others swallow their prey whole and alive.15:8155

After eating, snakes become dormant while the process of digestion takes place.58 Digestion 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 a large role in snake digestion. The ideal temperature for snakes to digest is 30 °C (86 °F). So much metabolic energy is involved in a snake's digestion that in the Mexican rattlesnake (Crotalus durissus), surface body temperature increases by as much as 1.2 °C (2.2 °F) during the digestive process.59 Because of this, a snake disturbed after having eaten recently will often regurgitate its prey to be able to escape the perceived threat. When undisturbed, the digestive process is highly efficient, with the snake's digestive enzymes dissolving and absorbing everything but the prey's hair (or feathers) and claws, which are excreted along with waste.



Lateral undulation

Main article: Undulatory locomotion

Lateral undulation is the sole mode of aquatic locomotion, and the most common mode of terrestrial locomotion.61 In this mode, the body of the snake alternately flexes to the left and right, resulting in a series of rearward-moving "waves".60 While this movement appears rapid, snakes have rarely been documented moving faster than two body-lengths per second, often much less.62 This mode of movement has the same net cost of transport (calories burned per meter moved) as running in lizards of the same mass.63


Terrestrial lateral undulation is the most common mode of terrestrial locomotion for most snake species.60 In this mode, the posteriorly moving waves push against contact points in the environment, such as rocks, twigs, irregularities in the soil, etc.60 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.64 The speed of this movement depends upon the density of push-points in the environment, with a medium density of about 8 along the snake's length being ideal.62 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.64

Main article: Sea snake
Banded sea krait, Laticauda sp.

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.65 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.66 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).60


See also: Sidewinding
A neonate sidewinder rattlesnake (Crotalus cerastes) sidewinding.

Most often employed by colubroid snakes (colubrids, elapids, and 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.6768 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.67 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 ⅓ of the cost for a lizard or snake to move the same distance.63 Contrary to popular belief, there is no evidence that sidewinding is associated with the sand being hot.67


Main article: 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.6068 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.67 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.63 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.


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.69 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.69 The ribs of the snake do not move in this mode of locomotion and this method is most often used by large pythons, boas, and vipers when stalking prey across open ground as the snake's movements are subtle and harder to detect by their prey in this manner.67


The movement of snakes in arboreal habitats has only recently been studied.70 While on tree branches, snakes use several modes of locomotion depending on species and bark texture.70 In general, snakes will use a modified form of concertina locomotion on smooth branches, but will laterally undulate if contact points are available.70 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'.70

Gliding snakes (Chrysopelea) of Southeast Asia launch themselves from branch tips, spreading their ribs and laterally undulating as they glide between trees.677172 These snakes can perform a controlled glide for hundreds of feet depending upon launch altitude and can even turn in midair.6771

Interactions with humans

Most common symptoms of any kind of snake bite envenomation.7374 Furthermore, there is vast variation in symptoms between bites from different types of snakes.73


Main article: Snakebite
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 designed 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.15:209 The World Health Organisation lists snakebite under the "other neglected conditions" category.75


The treatment for a snakebite is as variable as the bite itself. The most common and effective method is through antivenom (or antivenin), a serum made from the venom of the snake. Some antivenom is species-specific (monovalent) while some is made for use with multiple species in mind (polyvalent). In the United States for example, all species of venomous snakes are pit vipers, with the exception of the coral snake. To produce antivenom, a mixture of the venoms of the different species of rattlesnakes, copperheads, and cottonmouths is injected into the body of a horse in ever-increasing dosages until the horse is immunized. Blood is then extracted from the immunized horse. The serum is separated and further purified and freeze-dried. It is reconstituted with sterile water and becomes antivenom. For this reason, people who are allergic to horses are more likely to suffer an allergic reaction to antivenom.77 Antivenom for the more dangerous species (such as mambas, taipans, and cobras) is made in a similar manner in India, South Africa, and Australia, although these antivenoms are species-specific.

Snake charmers

Main article: Snake charming
An Indian cobra in a basket with a snake charmer. These snakes are perhaps the most common subjects 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 that contains a snake that he seemingly charms by playing tunes from his flutelike musical instrument, to which the snake responds.78 Snakes lack external ears, though they do have internal ears, and respond to the movement of the flute, not the actual noise.7879



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 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.80 The Irulas are also known to eat some of the snakes they catch and are very useful in rat extermination in the villages.

Despite the existence of snake charmers, there have also been professional snake catchers or 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.


A "海豹蛇" ("sea-leopard snake", supposedly Enhydris bocourti) occupies a place of honor among the live delicacies waiting to meet their consumers outside of a Guangzhou restaurant.
Snake meat, in a Taipei restaurant

While not commonly thought of as food in most cultures, in some cultures, the consumption of snakes is acceptable, or even considered a delicacy, prized for its alleged pharmaceutical effect of warming the heart. Snake soup of Cantonese cuisine is consumed by local people in autumn, to warm up their body. Western cultures document the consumption of snakes under extreme circumstances of hunger.81 Cooked rattlesnake meat is an exception, which is commonly consumed in parts of the Midwestern United States. In Asian countries such as China, Taiwan, Thailand, Indonesia, Vietnam and Cambodia, drinking the blood of snakes—particularly the cobra—is believed to increase sexual virility.82 The blood is drained while the cobra is still alive when possible, and is usually mixed with some form of liquor to improve the taste.82


U.S. Army Special Forces trainees are taught to catch, kill, and eat snakes during their survival course; this has earned them the nickname "snake eaters", which the video game Metal Gear Solid 3: Snake Eater may be inferred to draw from.

Snake wine (蛇酒) is an alcoholic beverage produced by infusing whole snakes in rice wine or grain alcohol. The drink was first recorded to have been consumed in China during the Western Zhou dynasty and considered an important curative and believed to reinvigorate a person according to Traditional Chinese medicine.84


In the Western world, some snakes (especially docile species such as the ball python and corn snake) are kept as pets. To meet this demand a captive breeding industry has developed. Snakes bred in captivity tend to make better pets and are considered preferable to wild caught specimens.85 Snakes can be very low maintenance pets, especially compared to more traditional species. They require minimal space, as most common species do not exceed five feet (1.5 m) in length. Pet snakes can be fed relatively infrequently, usually once every 5 to 14 days. Certain snakes have a lifespan of more than 40 years if given proper care.


Main article: Serpent (symbolism)


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).
Medusa by 16th Century Italian artist Caravaggio.
Imperial Japan depicted as an evil snake in a WWII propaganda poster

In Greek mythology snakes are often associated with deadly and dangerous antagonists, but this is not to say that snakes are symbolic of evil; in fact, snakes are a chthonic symbol, roughly translated as 'earthbound'. The nine-headed Lernaean Hydra that Hercules defeated and the three Gorgon sisters are children of Gaia, the earth.86 Medusa was one of the three Gorgon sisters who Perseus defeated.86 Medusa is described as a hideous mortal, with snakes instead of hair and the power to turn men to stone with her gaze.86 After killing her, Perseus gave her head to Athena who fixed it to her shield called the Aegis.86 The Titans are also depicted in art with snakes instead of legs and feet for the same reason—they are children of Gaia and Uranus, so they are bound to the earth.

U.S. President Theodore Roosevelt depicted as the infant Hercules grappling with a giant snake representing the Standard Oil Company.

The legendary account of the foundation of 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).


India is often called the land of snakes and is steeped in tradition regarding snakes.87 Snakes are worshipped as gods even today with many women pouring milk on snake pits (despite snakes' aversion for milk).87 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.88 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 Nāga.

In India there is another mythology about snakes. Commonly known in Hindi as "Ichchhadhari" snakes. Such snakes can take the form of any living creature, but prefer human form. These mythical snakes possess a valuable gem called "Mani", which is more brilliant than diamond. There are many stories in India about greedy people trying to possess this gem and ending up getting killed.

The ouroboros is a symbol associated with many different religions and customs, and is claimed to be related to alchemy. The ouroboros or uroboros is a snake eating its own tail in a clock-wise direction (from the head to the tail) in the shape of a circle, representing the cycle of life, death and rebirth, leading to immortality.


Many ancient Peruvian cultures worshipped nature.89 They emphasized animals and often depicted snakes in their art.90


Main article: Snake worship
A snake associated with Saint Simeon Stylites.
Rod of Asclepius, in which the snake, through ecdysis, symbolizes healing.

Snakes are a part of Hindu worship. A festival, Nag Panchami, in which participants worship either images of or live Nāgas (cobras) is celebrated every year. Most images of Lord Shiva depict snake around his neck. Puranas have various stories associated with snakes. In the Puranas, 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. He is sometimes referred to as "Ananta-Shesha", which means "Endless Shesha". Other notable snakes in Hinduism are Ananta, Vasuki, Taxak, Karkotaka and Pingala. The term Nāga is used to refer to entities that take the form of large snakes in Hinduism and Buddhism.

Snakes have also been widely revered, such as in ancient Greece, where the serpent was seen as a healer. Asclepius carried a serpent wound around his wand, a symbol seen today on many ambulances.

In religious terms, the snake and jaguar are arguably the most important animals in ancient Mesoamerica. "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."91 In both Maya and Aztec calendars, the fifth day of the week was known as Snake Day.

In Judaism, the snake of brass is also a symbol of healing, of one's life being saved from imminent death (Book of Numbers 21:6–9).

In some parts of Christianity, Christ's redemptive work is compared to saving one's life through beholding the Nehushtan (serpent of brass) (Gospel of John 3:14). Snake handlers use snakes as an integral part of church worship in order to exhibit their faith in divine protection. However, more commonly in Christianity, the serpent has been seen as a representative of evil and sly plotting, which can be seen in the description in Genesis chapter 3 of a snake in the Garden of Eden tempting Eve. Saint Patrick is reputed to have expelled all snakes from Ireland while Christianising the country in the 5th century, thus explaining the absence of snakes there.



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.92


The cyto-toxic effect of snake venom is being researched as a potential treatment for cancers.93

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Further reading

  • Behler, John L.; King, F. Wayne (1979). The Audubon Society Field Guide to Reptiles and Amphibians of North America. New York: Alfred A. Knopf. p. 581. ISBN 0-394-50824-6. 
  • Bullfinch, Thomas (2000). Bullfinch's Complete Mythology. London: Chancellor Press. p. 679. ISBN 0-7537-0381-5. 
  • Coborn, John (1991). The Atlas of Snakes of the World. New Jersey: TFH Publications. ISBN 978-0-86622-749-0. 
  • Conant, Roger; Collins, Joseph (1991). A Field Guide to Reptiles and Amphibians Eastern/Central North America. Boston: Houghton Mifflin Company. ISBN 0-395-58389-6. 
  • Deane, John (1833). The Worship of the Serpent. Whitefish, Montana: Kessinger Publishing. p. 412. ISBN 1-56459-898-5. 
  • Ditmars, Raymond L (1906). Poisonous Snakes of the United States: How to Distinguish Them. New York: E. R. Sanborn. p. 11. 
  • Ditmars, Raymond L (1931). Snakes of the World. New York: Macmillan. p. 11. ISBN 978-0-02-531730-7. 
  • Ditmars, Raymond L; W. Bridges (1935). Snake-Hunters' Holiday. New York: D. Appleton and Company. p. 309. 
  • Ditmars, Raymond L (1939). A Field Book of North American Snakes. Garden City, New York: Doubleday, Doran & Co. p. 305. 
  • Gibbons, J. Whitfield; Gibbons, Whit (1983). Their Blood Runs Cold: Adventures With Reptiles and Amphibians. Alabama: University of Alabama Press. p. 164. ISBN 978-0-8173-0135-4. 
  • Mattison, Chris (2007). The New Encyclopedia of Snakes. New Jersey: Princeton University Press. p. 272. ISBN 978-0-691-13295-2. 
  • McDiarmid, RW; Campbell, JA; Touré, T (1999). Snake Species of the World: A Taxonomic and Geographic Reference 1. Herpetologists' League. p. 511. ISBN 1-893777-00-6. 
  • Mehrtens, John (1987). Living Snakes of the World in Color. New York: Sterling. ISBN 0-8069-6461-8. 
  • Nóbrega Alves, RôMulo Romeu; Silva Vieira, Washington Luiz; Santana, Gindomar Gomes (2008). "Reptiles used in traditional folk medicine: conservation implications". Biodiversity and Conservation 17 (8): 2037–2049. doi:10.1007/s10531-007-9305-0. 
  • Romulus Whitaker (1996). நம்மை சுட்ரியுள்ள பாம்புகள் (Snakes around us, Tamil). National Book Trust. ISBN 81-237-1905-1. 
  • Rosenfeld, Arthur (1989). Exotic Pets. New York: Simon & Schuster. p. 293. ISBN 978-0-671-47654-0. 
  • Spawls, Steven; Branch, Bill (1995). The Dangerous Snakes of Africa. Sanibel Island, Florida: Ralph Curtis Publishing. p. 192. ISBN 0-88359-029-8. 

External links