Snakes are elongated, legless, carnivorous reptiles of the suborder
Serpentes. Like all squamates, snakes are ectothermic, amniote
vertebrates covered in overlapping scales. Many species of snakes have
skulls with several more joints than their lizard ancestors, enabling
them to swallow prey much larger than their heads with their highly
mobile jaws. 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 have only one functional lung. Some species retain a
pelvic girdle with a pair of vestigial claws on either side of the
cloaca. Lizards have evolved elongate bodies without limbs or with
greatly reduced limbs about twenty five times independently via
convergent evolution, leading to many lineages of legless lizards.
Legless lizards 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
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, the Hawaiian archipelago, and the
islands of New Zealand, and many small islands of the Atlantic and
central Pacific oceans. Additionally, sea snakes are widespread
throughout the Indian and Pacific Oceans. More than 20 families are
currently recognized, comprising about 520 genera and about 3,600
species. They range in size from the tiny, 10.4 cm
(4.1 in)-long thread snake to the reticulated python of 6.95
meters (22.8 ft) in length. The fossil species Titanoboa
cerrejonensis was 12.8 meters (42 ft) long. Snakes are thought
to have evolved from either burrowing or aquatic lizards, perhaps
Jurassic period, with the earliest known fossils dating to
between 143 and 167 Ma ago. 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.
Most species are nonvenomous and those that have venom use it
primarily to kill and subdue prey rather than for self-defense. Some
possess venom potent enough to cause painful injury or death to
humans. Nonvenomous snakes either swallow prey alive or kill by
4.2 Legless lizards
5.5 Internal organs
5.8 Facultative parthenogenesis
6.1 Winter dormancy
6.2 Feeding and diet
6.3.1 Lateral undulation
7 Interactions with humans
8 See also
10 Further reading
11 External links
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
"snake". The word ousted adder, as adder went on to narrow in
meaning, though in
Old English næddre was the general word for
snake. The other term, serpent, is from French, ultimately from
Indo-European *serp- (to creep), which also gave Ancient Greek
hérpō (ἕρπω) "I crawl".
A phylogenetic overview of the extant groups
Note: the tree only indicates relationships, not evolutionary
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
The earliest known true snake fossils (members of the crown group
Serpentes) come from the marine simoliophiids, the oldest of which is
Late Cretaceous (
Haasiophis terrasanctus, dated
to between 112 and 94 million years old.
Based on comparative anatomy, there is consensus that snakes descended
from lizards.:11 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.:11 The
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 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
Many modern snake groups originated during the Paleocene, alongside
the adaptive radiation of mammals following the extinction of
(non-avian) dinosaurs. The expansion of grasslands in North America
also led to an explosive radiation among snakes. 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 vipers and elapids in North
America and the significant diversification of
the origin of many modern genera such as Nerodia, Lampropeltis,
Pituophis, and Pantherophis).
There is fossil evidence to suggest that snakes may have evolved from
burrowing lizards, such as the varanids (or a similar group) during
Cretaceous Period. An early fossil snake relative, Najash
rionegrina, was a two-legged burrowing animal with a sacrum, and was
fully terrestrial. One extant analog of these putative ancestors
is the earless monitor Lanthanotus of
Borneo (though it also is
semiaquatic). Subterranean species evolved bodies streamlined for
burrowing, and eventually lost their limbs. 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. 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.
Fossil of Archaeophis proavus.
This hypothesis was strengthened in 2015 by the discovery of a 113m
year-old fossil of a four-legged snake in Brazil that has been named
Tetrapodophis amplectus. It has many snake-like features, is adapted
for burrowing and its stomach indicates that it was preying on other
animals. It is currently uncertain if
Tetrapodophis is a snake or
another species, in the 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.
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. 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 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
Cretaceous indicate deeper fossil records for these groups,
which may potentially refute either hypothesis.
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.
There are over 2,900 species of snakes ranging as far northward as the
Arctic Circle in Scandinavia and southward through Australia.
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.:143 There are numerous islands from which snakes are
absent, such as Ireland, Iceland, and New Zealand (although New
Zealand's waters are infrequently visited by the yellow-bellied sea
snake and the banded sea krait).
See also: List of snake genera
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:
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, 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
Pythonidae as one family,
while some keep the
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
Alethinophidia 19 families
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
False coral snake
Tropical South America.
Cundall, Wallach, 1993
Dwarf pipe snakes
West Malaysia and on the Indonesian island of Sumatra.
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.
Widespread on all continents, except Antarctica.
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.
On land, worldwide in tropical and subtropical regions, except in
Europe. Sea snakes occur in the Indian Ocean and the Pacific.
Southeastern Asia and northern Australia.
Lamprophiids (includes former
Atractaspididae as well as 6 other
subfamilies formerly considered colubrids)
Africa, southern Europe, and western-central Asia; two species into
Mexican burrowing snake
Along the Pacific versant from Mexico south to Costa Rica.
Southeast Asia and islands on the Sunda Shelf (Sumatra, Borneo, Java,
and their surrounding smaller islands).
Subsaharan Africa, India, Myanmar, southern China, Southeast Asia and
from the Philippines southeast through Indonesia to New Guinea and
West Indies; also Panama and northwestern South America, as well as in
northwestern and southeastern Brazil.
Southern India and Sri Lanka.
The Americas, Africa, and Eurasia east to Wallace's Line.
Dragon & odd-scaled snakes
Southern and southeastern Asia, and islands on the Sunda Shelf
(Sumatra, Borneo, Java, and their surrounding smaller islands).
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
Wallach & Günther, 1998
Borneo & peninsular Malaysia.
Scolecophidia 5 families
Primitive blind snakes
From southern Central America to northwestern South America. Disjunct
populations in northeastern and southeastern South America.
Vidal, Wynn, Donnellan and Hedges 2010
Southern & southeastern Asia, including Sri Lanka, the
Philippines, and New Guinea.
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.
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.
Vidal, Vences, Branch and Hedges 2010
Main article: Legless lizard
While snakes are limbless reptiles, which evolved from (and are
grouped with) lizards, there are many other species of lizards which
have lost their limbs independently and superficially look similar to
snakes. These include the slowworm and glass snake.
An adult Barbados threadsnake, Leptotyphlops carlae, on an American
The now extinct
Titanoboa cerrejonensis snakes found were 12.8 m
(42 ft) in length. By comparison, the largest extant snakes
are the reticulated python, which measures about 6.95 m
(22.8 ft) long, and the anaconda, which measures about
5.21 m (17.1 ft) long and is considered the heaviest snake
on Earth at 97.5 kg (215 lb).
At the other end of the scale, the smallest extant snake is
Leptotyphlops carlae, with a length of about 10.4 cm
(4.1 in). Most snakes are fairly small animals, approximately
1 m (3.3 ft) in length.
Thermographic image of a snake eating a mouse.
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. 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.
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. The fork in the tongue gives snakes a sort of
directional sense of smell and taste simultaneously. 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
A line diagram from G.A. Boulenger's
Fauna of British India
Fauna of British India (1890)
illustrating the terminology of shields on the head of a snake.
The underside is very sensitive to vibration. This allows snakes to be
able to sense approaching animals by detecting faint vibrations in the
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.
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.
The skin of a snake is covered in scales. Contrary to the popular
notion of snakes being slimy because of possible confusion of snakes
with worms, snakeskin has a smooth, dry texture. Most snakes use
specialized belly scales to travel, gripping surfaces. The body scales
may be smooth, keeled, or granular. The eyelids of a snake are
transparent "spectacle" scales, which remain permanently closed, also
known as brille.
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.
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.
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"
(Caenophidian) snakes, the broad belly scales and rows of dorsal
scales correspond to the vertebrae, allowing scientists to count the
vertebrae without dissection.
A snake shedding its skin.
Molting, or ecdysis, serves a number of functions. Firstly, the old
and worn skin is replaced; secondly, it helps get rid of parasites
such as mites and ticks. Renewal of the skin by moulting is supposed
to allow growth in some animals such as insects; however, this has
been disputed in the case of snakes.
Molting occurs periodically throughout the snake's life. Before a
molt, the snake stops eating and often hides or moves to a safe place.
Just before shedding, the skin becomes dull and dry looking and the
eyes become cloudy or blue-colored. The inner surface of the old skin
liquefies. This causes the old skin to separate from the new skin
beneath it. After a few days, the eyes clear and the snake "crawls"
out of its old skin. The old skin breaks near the mouth and the snake
wriggles out, aided by rubbing against rough surfaces. In many cases,
the cast skin peels backward over the body from head to tail in one
piece, like pulling a sock off inside-out. A new, larger, brighter
layer of skin has formed underneath.
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.
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. This periodic renewal has led to the snake
being a symbol of healing and medicine, as pictured in the Rod of
Scale counts can sometimes be used to tell the sex of a snake when the
species is not distinctly sexually dimorphic. A probe is inserted into
the cloaca until it can go no further. The probe is marked at the
point where it stops, removed, and compared to the subcaudal depth by
laying it alongside the scales. The scalation count determines
whether the snake is a male or female as hemipenes of a male will
probe to a different depth (usually longer) than the cloaca of a
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 skeleton of most snakes consists solely of the skull, hyoid,
vertebral column, and ribs, though henophidian snakes retain vestiges
of the pelvis and rear limbs.
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. 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.
The hyoid is a small bone located posterior and ventral to the skull,
in the 'neck' region, which serves as an attachment for muscles of the
snake's tongue, as it does in all other tetrapods.
The vertebral column consists of anywhere between 200 and 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
Autotomy of the tail, a feature found in some lizards is absent in
most snakes. 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
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.
Snakes are polyphyodonts with teeth that are continuously
Anatomy of a snake.file info
rudimentary left lung
The snake's heart is encased in a sac, called the pericardium, located
at the bifurcation of the bronchi. The heart is able to move around,
however, 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 is located in fatty tissue
above the heart and is responsible for the generation of immune cells
in the blood. The cardiovascular system of snakes is also 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
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. 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. This 'saccular
lung' is used for hydrostatic purposes to adjust buoyancy in some
aquatic snakes and its function remains unknown in terrestrial
species. Many organs that are paired, such as kidneys or
reproductive organs, are staggered within the body, with one located
ahead of the other.
Snakes have no lymph nodes.
Venomous snake, and § Bite
Milk snakes are often mistaken for coral snakes whose venom is deadly
Cobras, vipers, and closely related species use venom to immobilize or
kill their prey. The venom is modified saliva, delivered through
fangs.: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.
are often prey specific—their role in self-defense is
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.:209
Certain birds, mammals, and other snakes (such as kingsnakes) that
prey on venomous snakes have developed resistance and even immunity to
Venomous snakes include three families of
snakes, and do not constitute a formal classification group used in
The 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. There are, however,
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 snakes in the U.S. state of Oregon
retains enough toxins in their livers from the newts they eat to be
effectively poisonous to small local predators (such as crows and
Snake venoms are complex mixtures of proteins, and are stored in venom
glands at the back of the head. In all venomous snakes, these
glands open through ducts into grooved or hollow teeth in the upper
jaw.:243 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. Almost all
snake venom contains hyaluronidase, an enzyme that ensures rapid
diffusion of the venom.: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. Some snakes that use neurotoxins (such as the mangrove
snake) have fangs in the back of their mouths, with the fangs curled
backwards. This makes it difficult both for the snake to use its
venom and for scientists to milk them. 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.: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. 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:
Elapids – cobras including king cobras, kraits, mambas, Australian
copperheads, sea snakes, and coral snakes.
Viperids – vipers, rattlesnakes, copperheads/cottonmouths, and
There is a third family containing the opistoglyphous (rear-fanged)
snakes (as well as the majority of other snake species):
Colubrids – boomslangs, tree snakes, vine snakes, mangrove snakes,
although not all colubrids are venomous.:209
Sexual selection in scaled reptiles
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. The hemipenes are often grooved, hooked, or spined in order
to grip the walls of the female's cloaca.
Most species of snakes lay eggs which they abandon 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. Most pythons coil around their egg-clutches and remain
with them until they hatch. 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.
Some species of snake are ovoviviparous and retain the eggs within
their bodies until they are almost ready to hatch. 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. Retention of eggs and live birth are most
often associated with colder environments.
The Garter snake has been studied for sexual selection
Sexual selection in snakes is demonstrated by the three thousand
species that each use different tactics in acquiring mates. Ritual
combat between males for the females they want to 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
forcing it downward. It is common for neck biting to occur while the
snakes are entwined.
Parthenogenesis is a natural form of reproduction in which growth and
development of embryos occur without fertilization. Agkistrodon
contortrix (copperhead) and
Agkistrodon piscivorus (cotton mouth) can
reproduce by facultative parthenogenesis. That is, they are capable of
switching from a sexual mode of reproduction to an asexual mode.
The type of parthenogenesis that likely occurs is 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 homozygosity, expression of deleterious recessive alleles
and often to developmental abnormalities. Both captive-born and
wild-born A. contortrix and A. piscivorus appear to be capable of this
form of parthenogenesis.
Reproduction in 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
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
Feeding and diet
Carpet python constricting and consuming a chicken.
African egg-eating snake eating an egg
All snakes are strictly carnivorous, eating small animals including
lizards, frogs, other snakes, small mammals, birds, eggs, fish, snails
or insects. 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. For example, the
African egg-eating snake has flexible jaws adapted for eating eggs
much larger than the diameter of its head.: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.: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. Snakes of the family
more teeth on the right side of their mouths than on the left, as the
shells of their prey usually spiral clockwise.:184
Some snakes have a venomous bite, which they use to kill their prey
before eating it. Other snakes kill their prey by
constriction. Still others swallow their prey whole and
Dolichophis jugularis preying on a Sheltopusik.
After eating, snakes become dormant while the process of digestion
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. 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.
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
Undulatory locomotion and Hydrophiinae
Crawling prints of a snake
Lateral undulation is the sole mode of aquatic locomotion, and the
most common mode of terrestrial locomotion. In this mode, the body
of the snake alternately flexes to the left and right, resulting in a
series of rearward-moving "waves". While this movement appears
rapid, snakes have rarely been documented moving faster than two
body-lengths per second, often much less. This mode of movement
has the same net cost of transport (calories burned per meter moved)
as running in lizards of the same mass.
Terrestrial lateral undulation is the most common mode of terrestrial
locomotion for most snake species. In this mode, the posteriorly
moving waves push against contact points in the environment, such as
rocks, twigs, irregularities in the soil, etc. 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. The speed of this
movement depends upon the density of push-points in the environment,
with a medium density of about 8[clarification needed] along the
snake's length being ideal. 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.
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. 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. All snakes can laterally
undulate forward (with backward-moving waves), but only sea snakes
have been observed reversing the motion (moving backwards with
Main article: 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. 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. 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 to move the same distance. Contrary
to popular belief, there is no evidence that sidewinding is associated
with the sand being hot.
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. 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. 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. 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.
Golden tree snake
Golden tree snake climbing a flower
The movement of snakes in arboreal habitats has only recently been
studied. While on tree branches, snakes use several modes of
locomotion depending on species and bark texture. In general,
snakes will use a modified form of concertina locomotion on smooth
branches, but will laterally undulate if contact points are
available. 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'.
Gliding snakes (Chrysopelea) of Southeast Asia launch themselves from
branch tips, spreading their ribs and laterally undulating as they
glide between trees. These snakes can perform a controlled
glide for hundreds of feet depending upon launch altitude and can even
turn in midair.
Main article: 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. 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. 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.
Interactions with humans
Most common symptoms of any kind of snake bite envenomation.
Furthermore, there is vast variation in symptoms between bites from
different types of snakes.
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.:209
The World Health Organisation (WHO) lists snakebite under the "other
neglected conditions" category.
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. 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.
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.
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.
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. Snakes lack external ears, though they
do have internal ears, and respond to the movement of the flute, not
the actual noise.
Wildlife Protection Act of 1972
Wildlife Protection Act of 1972 in India technically proscribes
snake charming on grounds of reducing animal cruelty. Other snake
charmers also have a snake and mongoose show, where both the animals
have a mock fight; however, this is not very common, as the snakes, as
well as the mongooses, 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 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
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. 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
occupies a place of honor among the live delicacies waiting to meet
their consumers outside of a
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
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.
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. 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.
In some Asian countries, the use of snakes in alcohol is also
accepted. In such cases, the body of a snake or several snakes is left
to steep in a jar or container of liquor. It is claimed that this
makes the liquor stronger (as well as more expensive). One example of
this is the Habu snake sometimes placed in the Okinawan liquor Awamori
also known as "Habu Sake".
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.
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. Snakes can be very low maintenance pets, especially
compared to more traditional species. They require minimal space, as
most common species do not exceed 5 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
Main article: Serpent (symbolism)
In Egyptian history, the snake occupies a primary role with the Nile
cobra adorning the crown of the pharaoh in ancient times. It was
worshipped as one of the gods and was also used for sinister purposes:
murder of an adversary and ritual suicide (Cleopatra).
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.
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
and the three
Gorgon sisters are children of Gaia, the earth.
Medusa was one of the three
Gorgon sisters who
Medusa is described as a hideous mortal, with snakes instead of hair
and the power to turn men to stone with her gaze. After killing
Perseus gave her head to
Athena who fixed it to her shield called
the Aegis. 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.
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
Cadmus all perished – leading to the term "Cadmean victory"
(i.e. a victory involving one's own ruin).
Rod of Asclepius, in which the snake, through ecdysis, symbolizes
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.
India is often called the land of snakes and is steeped in tradition
regarding snakes. Snakes are worshipped as gods even today with
many women pouring milk on snake pits (despite snakes' aversion for
milk). The cobra is seen on the neck of
depicted often as sleeping on a seven-headed snake or within the coils
of a serpent. 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.[citation
The snake is one of the 12 celestial animals of Chinese Zodiac, in the
Many ancient Peruvian cultures worshipped nature. They emphasized
animals and often depicted snakes in their art.
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A snake associated with Saint Simeon Stylites.
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
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,
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
Chichen Itza to Tenochtitlan, and the
coatl meaning serpent or twin, forms part of primary deities such as
Mixcoatl, Quetzalcoatl, and Coatlicue." In both Maya and Aztec
calendars, the fifth day of the week was known as
In Judaism, the snake of brass is also a symbol of healing, of one's
life being saved from imminent death.
In some parts of Christianity, Christ's redemptive work is compared to
saving one's life through beholding the
Nehushtan (serpent of
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
Saint Patrick is reputed to have expelled all
Ireland while converting the country to Christianity in
the 5th century, thus explaining the absence of snakes there.
In Christianity and Judaism, the snake makes its infamous appearance
in the first book of the Bible when a serpent appears before the first
couple Adam and
Eve and tempts them with the forbidden fruit from the
Tree of Knowledge. The snake returns in Exodus when Moses, as a
sign of God's power, turns his staff into a snake and when
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."
Neo-Paganism and Wicca, the snake is seen as a symbol of wisdom and
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.
The cytotoxic effect of snake venom is being researched as a potential
treatment for cancers.
Amphibians and reptiles portal
Legend of the White Snake
The Green Snake and the Beautiful Lily
The Green Snake and the Beautiful Lily (Goethe's archetypal tale of
List of Serpentes families
List of snakes
Spinal osteoarthropathy (reptile disease)
The New Encyclopedia of Snakes
The Snakes of Europe
The Snakes of Europe and Snakes of Europe Wikibooks:Snakes of Europe,
^ a b Hsiang, A. Y.; Field, D. J.; Webster, T. H.; Behlke, A. D.;
Davis, M. B.; Racicot, R. A.; Gauthier, J. A. (2015). "The origin of
snakes: Revealing the ecology, behavior, and evolutionary history of
early snakes using genomics, phenomics, and the fossil record". BMC
Evolutionary Biology. 15. doi:10.1186/s12862-015-0358-5.
PMC 4438441 . PMID 25989795.
^ Reeder, T. W.; Townsend, T. M.; Mulcahy, D. G.; Noonan, B. P.; Wood,
P. L.; Sites, J. W.; Wiens, J. J. (2015). "Integrated Analyses Resolve
Conflicts over Squamate
Reptile Phylogeny and Reveal Unexpected
Fossil Taxa". PLoS ONE. 10 (3): e0118199.
doi:10.1371/journal.pone.0118199. PMC 4372529 .
^ a b Roland Bauchot, ed. (1994). Snakes: A Natural History. New York:
Sterling Publishing Co., Inc. p. 220.
^ a b c "Serpentes". Integrated Taxonomic Information System.
Retrieved 4 April 2017.
^ a b c d e f g h i j k snake species list at the
Archived 2013-12-02 at the Wayback Machine.. Accessed 4 April 2017.
^ a b S. Blair Hedges (August 4, 2008). "At the lower size limit in
snakes: two new species of threadsnakes (Squamata: Leptotyphlopidae:
Leptotyphlops) from the Lesser Antilles" (PDF). Zootaxa. 1841: 1–30.
Archived (PDF) from the original on August 13, 2008. Retrieved
^ a b Fredriksson, G. M. (2005). "
Predation on Sun Bears by
Reticulated Python in East Kalimantan, Indonesian Borneo". Raffles
Bulletin of Zoology. 53 (1): 165–168. Archived from the original on
^ a b Head, Jason J.; Jonathan I. Bloch; Alexander K. Hastings; Jason
R. Bourque; Edwin A. Cadena; Fabiany A. Herrera; P. David Polly;
Carlos A. Jaramillo (February 2009). "Giant boid snake from the
paleocene neotropics reveals hotter past equatorial temperatures".
Nature. 457: 715–718. doi:10.1038/nature07671. PMID 19194448.
Archived from the original on 2009-02-08. Retrieved 2009-02-05.
^ Perkins, Sid (27 January 2015). "Fossils of oldest known snakes
unearthed". news.sciencemag.org. Archived from the original on 30
January 2015. Retrieved 29 January 2015.
Caldwell, M. W.; Nydam, R. L.; Palci, A.; Apesteguía, S. (2015). "The
oldest known snakes from the Middle Jurassic-Lower
insights on snake evolution". Nature Communications. 6 (5996): 5996.
doi:10.1038/ncomms6996. PMID 25625704.
^ Proto-IE: *(s)nēg-o-, Meaning: snake, Old Indian: nāgá- m.
"snake", Germanic: *snēk-a- m., *snak-an- m., *snak-ō f.; *snak-a-
vb., Russ. meaning: жаба (змея), References: WP
(Vergleichendes Wörterbuch der indogermanischen Sprachen) II 697 f.
^ Online Etymology Dictionary, s.v. "snake Archived 2010-07-19 at the
Wayback Machine.", retrieved on 22 September 2009.
^ "Definition of serpent". Merriam-Webster Online Dictionary. Archived
from the original on 17 October 2007. Retrieved 12 October 2006.
^ a b Lee, Michael S. Y.; Andrew F. Hugall, Robin Lawson & John D.
Scanlon (2007). "Phylogeny of snakes (Serpentes): combining
morphological and molecular data in likelihood, Bayesian and parsimony
analyses". Systematics and Biodiversity. 5 (4): 371–389.
^ Durand, J.F. (2004). "The origin of snakes". Geoscience Africa 2004.
Abstract Volume, University of the Witwatersrand, Johannesburg, South
Africa, pp. 187.
^ Vidal, N., Rage, J.-C., Couloux, A. and Hedges, S.B. (2009). "Snakes
(Serpentes)". Pp. 390–397 in Hedges, S. B. and Kumar, S. (eds.), The
Timetree of Life. Oxford University Press.
^ a b c d e f g h i j k l m n o p Mehrtens JM. 1987. Living Snakes of
the World in Color. New York: Sterling Publishers. 480 pp.
^ a b c d e Sanchez, Alejandro. "Diapsids III: Snakes". Father
Sanchez's Web Site of West Indian Natural History. Archived from the
original on 2007-11-27. Retrieved 2007-11-26.
^ a b "New
Snake With Legs". UNEP WCMC Database. Washington,
D.C.: American Association For The Advancement Of Science. Archived
from the original on 2007-12-25. Retrieved 2007-11-29.
^ a b Holman, J. Alan (2000).
Fossil Snakes of North America (First
ed.). Bloomington, IN: Indiana University Press. pp. 284–323.
^ a b Mc Dowell, Samuel (1972). "The evolution of the tongue of snakes
and its bearing on snake origins". Evolutionary Biology. 6: 191–273.
doi:10.1007/978-1-4684-9063-3_8. ISBN 978-1-4684-9065-7.
^ Apesteguía, Sebastián; Zaher, Hussam (April 2006). "A Cretaceous
terrestrial snake with robust hindlimbs and a sacrum". Nature. 440
(7087): 1037–1040. doi:10.1038/nature04413. PMID 16625194.
Archived from the original on 2007-12-18. Retrieved 2007-11-29.
^ a b c Mertens, Robert (1961). "Lanthanotus: an important lizard in
evolution". Sarawak Museum Journal. 10: 320–322.
^ Jonathan, Webb (24 July 2014). "Four-legged snake ancestor 'dug
burrows'". BBC Science & Environment. Archived from the original
on 26 July 2015. Retrieved Jul 24, 2015.
^ Yong, Ed. "A
Snake With Four Legs". Archived from the
original on 2015-07-23. Retrieved 2015-07-24.
^ Martill, David M.; Tischlinger, Helmut; Longrich, Nicholas R.
(2015-07-24). "A four-legged snake from the Early
Gondwana". Science. 349 (6246): 416–419.
doi:10.1126/science.aaa9208. ISSN 0036-8075. PMID 26206932.
Archived from the original on 2015-07-26.
^ "What a Legless Mouse Tells Us About
Snake Evolution". The Atlantic.
Archived from the original on 2016-10-24. Retrieved 2016-10-25.
^ "Snakes Used to Have Legs and Arms … Until These Mutations
Happened". Live Science. Archived from the original on 2016-10-22.
^ Leal, Francisca (2016). "Loss and Re-emergence of Legs in Snakes by
Modular Evolution of
Sonic hedgehog and HOXD Enhancers". Current
Biology. 26: 2966–2973. doi:10.1016/j.cub.2016.09.020.
^ Kvon, EZ; Kamneva, OK; Melo, US; Barozzi, I; Osterwalder, M;
Mannion, BJ; Tissières, 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 (2016). "Progressive Loss of
Function in a Limb Enhancer during
Snake Evolution". Cell. 167:
633–642.e11. doi:10.1016/j.cell.2016.09.028. PMC 5484524 .
^ a b Conant R, Collins JT. 1991. A Field Guide to Reptiles and
Amphibians: Eastern and Central North America. Houghton Mifflin,
Boston. 450 pp. 48 plates. ISBN 0-395-37022-1.
^ Natural History Information Centre;
Auckland War Memorial Museum.
"Natural History Questions".
Auckland War Memorial Museum Tamaki
Paenga Hira. Auckland, New Zealand:
Auckland War Memorial Museum. Q.
Are there any snakes in New Zealand?. Archived from the original on 12
July 2012. Retrieved 26 April 2012.
^ Pough; et al. (2002) . Herpetology: Third Edition. Pearson
Prentice Hall. ISBN 0-13-100849-8.
^ a b McDiarmid RW, Campbell JA, Touré T. 1999.
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).
^ Spawls S, Howell K, Drewes R, Ashe J. 2004. A Field Guide To The
Reptiles Of East Africa. London: A & C Black Publishers Ltd. 543
pp. ISBN 0-7136-6817-2.
Elapidae at the Reptarium.cz
Reptile Database. Accessed 3 December
^ Rivas, Jesús Antonio (2000). The life history of the green anaconda
(Eunectes murinus), with emphasis on its reproductive Biology (PDF)
(Ph.D. thesis). University of Tennessee. Archived (PDF) from the
original on 2016-03-03.
^ Boback, S. M.; Guyer, C. (2003). "Empirical Evidence for an Optimal
Body Size in Snakes". Evolution. 57 (2): 345–351.
ISSN 0014-3820. PMID 12683530.
^ a b c d e Cogger(1991), p. 180.
Reptile Senses: Understanding Their World". Petplace.com.
2015-05-18. Archived from the original on 2015-02-19. Retrieved
^ Smith, Malcolm A. The Fauna of British India, Including Ceylon and
Burma. Vol I, Loricata and Testudines. p. 30.
^ a b c d  Archived August 5, 2006, at the Wayback Machine.
^ "ZooPax: A Matter of Scale: Part III". Whozoo.org. Archived from the
original on 2016-01-16. Retrieved 2016-01-09.
^ a b  Archived November 25, 2007, at the Wayback Machine.
^ a b Wilcox, Robert A; Whitham, Emma M (15 April 2003). "The symbol
of modern medicine: why one snake is more than two". Annals of
Internal Medicine. 138 (8): 673–7.
doi:10.7326/0003-4819-138-8-200304150-00016. PMID 12693891.
Archived from the original on 19 December 2007. Retrieved
^ a b c Rosenfeld (1989), p. 11.
^ Harline, P H (1971). "Physiological basis for detection of sound and
vibration in snakes" (PDF). J. Exp. Biol. 54 (2): 349–371. Archived
(PDF) from the original on 2008-12-17.
^ Friedel, P; Young, BA; van Hemmen, JL (2008). "Auditory Localization
of Ground-Borne Vibrations in Snakes". Phys. Rev. Lett. 100: 048701.
doi:10.1103/physrevlett.100.048701. PMID 18352341.
^ Lisa Zyga (2008-02-13). "Desert
Snake Hears Mouse Footsteps with its
Jaw". PhysOrg. Archived from the original on 2011-10-10.
^ Cogger, H 1993 Fauna of Australia. Vol. 2A Amphibia and Reptilia.
Australian Biological Resources Studies, Canberra.
^ Arnold, E.N. (1984). "Evolutionary aspects of tail shedding in
lizards and their relatives". Journal of Natural History. 18 (1):
^ Ananjeva, N. B.; Orlov, N. L. (1994). "Caudal autotomy in Colubrid
Xenochrophis piscator from Vietnam". Russian Journal of
Herpetology. 1 (2).
^ Gaete, Marcia; Tucker, Abigail S. (2013). "Organized Emergence of
Multiple-Generations of Teeth in Snakes Is Dysregulated by Activation
of Wnt/Beta-Catenin Signalling". PLOS ONE. 8 (9): e74484.
doi:10.1371/journal.pone.0074484. PMC 3760860 .
^ a b c d e f Mader, Douglas (June 1995). "Reptilian Anatomy".
Reptiles. 3 (2): 84–93.
^ a b c d e Freiberg (1984), p. 125.
^ a b Freiberg (1984), p. 123.
^ a b c d Freiberg (1984), p. 126.
^ Fry, Brian G.; Vidal, Nicholas; Norman, Janette A.; Vonk, Freek J.;
Scheib, Holger; Ramjan, S. F. Ryan; Kuruppu, Sanjaya; Fung, Kim;
Hedges, S. Blair; Richardson, Michael K.; Hodgson, Wayne C.;
Ignjatovic, Vera; Summerhayes, Robyn; Kochva, Elazar (2006). "Early
evolution of the venom system in lizards and snakes". Nature. 439
(7076): 584–588. doi:10.1038/nature04328. PMID 16292255.
^ a b c d Capula (1989), p. 117.
^ Robert D. Aldridge; David M. Sever (19 April 2016). Reproductive
Biology and Phylogeny of Snakes. CRC Press.
^ a b Cogger (1991), p. 186.
^ a b Capula (1989), p. 118.
^ a b c Cogger (1991), p. 182.
^ Shine, Richard; Langkilde, Tracy; Mason, Robert T (2004). "Courtship
tactics in garter snakes: How do a male's morphology and behaviour
influence his mating success?".
Animal Behaviour. 67 (3): 477–83.
^ Blouin-Demers, Gabriel; Gibbs, H. Lisle; Weatherhead, Patrick J.
(2005). "Genetic evidence for sexual selection in black ratsnakes,
Animal Behaviour. 69 (1): 225–34.
^ a b Booth W, Smith CF, Eskridge PH, Hoss SK, Mendelson JR, Schuett
GW (2012). "Facultative parthenogenesis discovered in wild
vertebrates". Biol. Lett. 8 (6): 983–5. doi:10.1098/rsbl.2012.0666.
PMC 3497136 . PMID 22977071.
^ Booth W, Million L, Reynolds RG, Burghardt GM, Vargo EL, Schal C,
Tzika AC, Schuett GW (2011). "Consecutive virgin births in the new
world boid snake, the Colombian rainbow Boa, Epicrates maurus". J.
Hered. 102 (6): 759–63. doi:10.1093/jhered/esr080.
^ a b c d e Behler (1979) p. 581
^ Hori, Michio; Asami, Takahiro; Hoso, Masaki (2007). "Right-handed
snakes: convergent evolution of asymmetry for functional
specialization". Biology Letters. 3 (2): 169–72.
doi:10.1098/rsbl.2006.0600. PMC 2375934 .
^ Pyron, RA; Burbrink, F; Wiens, JJ (2013). "A phylogeny and revised
classification of Squamata, including 4161 species of lizards and
snakes". BMC Evolutionary Biology. 13: 93.
^ Freiberg (1984), pp. 125–127.
^ Tattersall, GJ; Milsom, WK; Abe, AS; Brito, SP; Andrade, DV (2004).
"The thermogenesis of digestion in rattlesnakes". Journal of
Experimental Biology. The Company of Biologists. 207 (Pt 4):
579–585. doi:10.1242/jeb.00790. PMID 14718501. Archived from
the original on 2005-11-30. Retrieved 2006-05-26.
^ a b c d e f Cogger(1991), p. 175.
^ a b Gray, J. (1946). "The mechanism of locomotion in snakes".
Journal of Experimental Biology. 23 (2): 101–120.
^ a b Hekrotte, Carlton (1967). "Relations of Body Temperature, Size,
and Crawling Speed of the Common Garter Snake, Thamnophis s.
sirtalis". Copeia. 23 (4): 759–763. doi:10.2307/1441886.
^ a b c Walton, M.; Jayne, B. C.; Bennett, A. F. (1967). "The
energetic cost of limbless locomotion". Science. 249 (4968):
524–527. doi:10.1126/science.249.4968.524. PMID 17735283.
^ a b Gray, J; H.W., H (1950). "Kinetics of locomotion of the grass
snake". Journal of Experimental Biology. 26 (4): 354–367. Archived
from the original on 2008-07-09.
^ Gray, J; Lissman (1953). "Undulatory propulsion". Quarterly Journal
of Microscopical Science. 94: 551–578.
^ Jayne, B. C. (1988). "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 of Morphology. 197 (2): 159–181.
doi:10.1002/jmor.1051970204. PMID 3184194.
^ a b c d e f g Cogger(1991), p. 177.
^ a b Jayne, B.C. (1986). "Kinematics of terrestrial snake
locomotion". Copeia. 1986 (4): 915–927. doi:10.2307/1445288.
^ a b c d Astley, H.C.; Jayne, B.C. (2007). "Effects of perch diameter
and incline on the kinematics, performance and modes of arboreal
locomotion of corn snakes (Elaphe guttata)". Journal of Experimental
Biology. 210 (Pt 21): 3862–3872. doi:10.1242/jeb.009050.
^ a b Freiberg (1984), p. 135.
^ Socha, JJ (2002). "Gliding flight in the paradise tree snake".
Nature. 418 (6898): 603–604. doi:10.1038/418603a.
^ a b Cogger (1991), p. 176.
^ a b MedlinePlus >
Snake bites Archived 2010-12-04 at the Wayback
Machine. 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.
Snake Bite First Aid – Snakebite". Health-care-clinic.org.
Archived from the original on 2016-01-16. Retrieved 2016-01-09.
^ WHO. "The 17 neglected tropical diseases". WHO. WHO. Archived from
the original on 22 February 2014. Retrieved 24 October 2014.
^ Sinha, Kounteya (25 July 2006). "No more the land of snake
charmers..." The Times of India. Archived from the original on 21
Snakebite envenoming". World Health Organization. Archived from the
original on 2017-04-18. Retrieved 2017-10-27.
^ Dubinsky, I (1996). "
Rattlesnake bite in a patient with horse
allergy and von Willebrand's disease: case report" (PDF). Can Fam
Physician. 42: 2207–11. PMC 2146932 . PMID 8939322.
Archived (PDF) from the original on 2016-01-16. Retrieved
^ a b c Bagla, Pallava (April 23, 2002). "India's
Snake Charmers Fade,
Blaming Eco-Laws, TV". National Geographic News. Archived from the
original on December 18, 2007. Retrieved 2007-11-26.
Snake charmer's bluff" Archived 2016-08-18 at the Wayback Machine.
International Wildlife Encyclopedia, 3rd edition, page 482
^ Whitaker, Romulus & Captain, Ashok. Snakes of India: The Field
Guide. (2004) pp 11 to 13.
^ Irvine, F. R. (1954). "Snakes as food for man". British Journal of
Herpetology. 1 (10): 183–189.
^ a b Flynn, Eugene (April 23, 2002). "Flynn Of The Orient Meets The
Cobra". Fabulous Travel. Archived from the original on November 17,
2007. Retrieved 2007-11-26.
^ Allen, David (July 22, 2001). "Okinawa's potent habu sake packs
healthy punch, poisonous snake". Stars and Stripes. Archived from the
original on November 28, 2007. Retrieved 2007-11-26.
^ "蛇酒的泡制与药用(The production and medicinal qualities of
snake wine)". 2007-04-09. Archived from the original on
^ Ernest, Carl; George R. Zug; Molly Dwyer Griffin (1996). Snakes in
Question: The Smithsonian Answer Book. Washington, D.C.: Smithsonian
Books. p. 203. ISBN 1-56098-648-4.
^ a b c d Bullfinch (2000) p. 85.
^ a b Deane (1833). p. 61.
^ Deane (1833). pp. 62–64.
^ "The Chinese Calendar". timeanddate.com. Archived from the original
on 15 August 2017. Retrieved 1 June 2017.
^ Benson, Elizabeth (1972). The Mochica: A Culture of Peru. London:
Thames and Hudson. ISBN 0-500-72001-0.
^ Berrin, Katherine;
Larco Museum (1997). The Spirit of Ancient Peru:
Treasures from the Museo Arqueológico Rafael Larco Herrera. New York:
Thames and Hudson. ISBN 978-0-500-01802-6.
^ The Gods and Symbols of Ancient Mexico and the Maya. Miller, Mary
1993 Thames & Hudson. London ISBN 978-0-500-27928-1
^ Numbers 21:6–21:9
^ John 3:14
^ a b Genesis 3:1
^ Revelation 20:2
^ Sharer, Robert J.; Loa P. Traxler (2006). The Ancient Maya (6th
(fully revised) ed.). Stanford, California: Stanford University Press.
p. 619. ISBN 0-8047-4817-9. OCLC 57577446.
^ Vivek Kumar Vyas, Keyur Brahmbahtt, Ustav Parmar; Brahmbhatt; Bhatt;
Parmar (February 2012). "Theraputic potential of snake venom in cancer
therapy: current perspective". Asian Pacific Journal of Tropical
Medicine. 3 (2): 156–162. doi:10.1016/S2221-1691(13)60042-8.
PMC 3627178 . PMID 23593597. CS1 maint: Multiple
names: authors list (link)
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. Archived from
the original on 2009-02-09.
Capula, Massimo; Behler (1989). Simon & Schuster's Guide to
Reptiles and Amphibians of the World. New York: Simon & Schuster.
Coborn, John (1991). The Atlas of Snakes of the World. New Jersey: TFH
Publications. ISBN 978-0-86622-749-0.
Cogger, Harold; Zweifel, Richard (1992). Reptiles & Amphibians.
Sydney: Weldon Owen. ISBN 0-8317-2786-1.
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 (1933). Reptiles of the World: The Crocodilians,
Lizards, Snakes, Turtles and Tortoises of the Eastern and Western
Hemispheres. New York: Macmillan. p. 321.
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.
Freiberg, Dr. Marcos; Walls, Jerry (1984). The World of Venomous
Animals. New Jersey: TFH Publications. ISBN 0-87666-567-9.
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.
McDiarmid, RW; Campbell, JA; Touré, T (1999).
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):
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.
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"Bibliography for "Serpentes"". Biodiversity Heritage Library.
"Serpentes". Integrated Taxonomic Information System.
"US Snakes". eNature. Archived from the original on 2008-03-15.
"Snakes of the Indian Subcontinent". Naturemagics Kerala Photo
"Herpetology Database". Swedish Museum of Natural History.
Snake news, and video clips from BBC programmes past and
Basics of snake taxonomy at Life is Short but Snakes are Long
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