Snakes are elongated,
limbless,
carnivorous
A carnivore , or meat-eater (Latin, ''caro'', genitive ''carnis'', meaning meat or "flesh" and ''vorare'' meaning "to devour"), is an animal or plant whose food and energy requirements derive from animal tissues (mainly muscle, fat and other sof ...
reptile
Reptiles, as most commonly defined are the animals in the class Reptilia ( ), a paraphyletic grouping comprising all sauropsids except birds. Living reptiles comprise turtles, crocodilians, squamates (lizards and snakes) and rhynchocephalians ( ...
s of the
suborder
Order ( la, ordo) is one of the eight major hierarchical taxonomic ranks in Linnaean taxonomy. It is classified between family and class. In biological classification, the order is a taxonomic rank used in the classification of organisms and ...
Serpentes . Like all other
squamates, snakes are
ectothermic,
amniote
Amniotes are a clade of tetrapod vertebrates that comprises sauropsids (including all reptiles and birds, and extinct parareptiles and non-avian dinosaurs) and synapsids (including pelycosaurs and therapsids such as mammals). They are disti ...
vertebrate
Vertebrates () comprise all animal taxa within the subphylum Vertebrata () ( chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, ...
s covered in overlapping
scales
Scale or scales may refer to:
Mathematics
* Scale (descriptive set theory), an object defined on a set of points
* Scale (ratio), the ratio of a linear dimension of a model to the corresponding dimension of the original
* Scale factor, a number w ...
. Many species of snakes have
skull
The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, the ...
s with several more joints than their
lizard
Lizards are a widespread group of squamate reptiles, with over 7,000 species, ranging across all continents except Antarctica, as well as most oceanic island chains. The group is paraphyletic since it excludes the snakes and Amphisbaenia alt ...
ancestors, enabling them to swallow prey much larger than their heads (
cranial kinesis). To accommodate their narrow bodies, snakes' paired organs (such as kidneys) appear one in front of the other instead of side by side, and most have only one functional
lung
The lungs are the primary organs of the respiratory system in humans and most other animals, including some snails and a small number of fish. In mammals and most other vertebrates, two lungs are located near the backbone on either side of t ...
. Some species retain a
pelvic girdle with a pair of
vestigial
Vestigiality is the retention, during the process of evolution, of genetically determined structures or attributes that have lost some or all of the ancestral function in a given species. Assessment of the vestigiality must generally rely on co ...
claws on either side of the
cloaca
In animal anatomy, a cloaca ( ), plural cloacae ( or ), is the posterior orifice that serves as the only opening for the digestive, reproductive, and urinary tracts (if present) of many vertebrate animals. All amphibians, reptiles and birds, a ...
. Lizards have evolved elongate bodies without limbs or with greatly reduced limbs about twenty-five times independently via
convergent evolution
Convergent evolution is the independent evolution of similar features in species of different periods or epochs in time. Convergent evolution creates analogous structures that have similar form or function but were not present in the last com ...
, leading to many lineages of
legless lizards. These resemble snakes, but several common groups of legless lizards have eyelids and external ears, which snakes lack, although this rule is not universal (see
Amphisbaenia
Amphisbaenia (called amphisbaenians or worm lizards) is a group of usually legless squamates, comprising over 200 extant species. Amphisbaenians are characterized by their long bodies, the reduction or loss of the limbs, and rudimentary eyes. As ...
,
Dibamidae, and
Pygopodidae).
Living snakes are found on every continent except Antarctica, and on most smaller land masses; exceptions include some large islands, such as Ireland, Iceland, Greenland, the
Hawaiian archipelago
The Hawaiian Islands ( haw, Nā Mokupuni o Hawai‘i) are an archipelago of eight major islands, several atolls, and numerous smaller islets in the North Pacific Ocean, extending some from the island of Hawaii in the south to northernmost Kur ...
, and the islands of New Zealand, as well as many small islands of the Atlantic and central Pacific oceans.
Additionally,
sea snakes
Sea snakes, or coral reef snakes, are elapid snakes that inhabit marine environments for most or all of their lives. They belong to two subfamilies, Hydrophiinae and Laticaudinae. Hydrophiinae also includes Australasian terrestrial snakes, where ...
are widespread throughout the Indian and Pacific oceans. Around thirty
families
Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Ideall ...
are currently recognized, comprising about 520
genera
Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nomenclat ...
and about 3,900
species
In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...
.
They range in size from the tiny,
Barbados threadsnake
The Barbados threadsnake (''Tetracheilostoma carlae'') is a species of threadsnake. It is the smallest known snake species. This member of the Leptotyphlopidae family is found on the Caribbean islands of Barbados and Anguilla.
Taxonomy and et ...
to the
reticulated python
The reticulated python (''Malayopython reticulatus'') is a python species native to South and Southeast Asia. It is the world's longest snake, and is among the three heaviest. It is listed as least concern on the IUCN Red List because of its wi ...
of in length.
The fossil species ''
Titanoboa cerrejonensis'' was long.
Snakes are thought to have evolved from either burrowing or aquatic lizards, perhaps during the
Jurassic
The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The J ...
period, with the earliest known fossils dating to between 143 and 167
Ma ago. The diversity of modern snakes appeared during the
Paleocene
The Paleocene, ( ) or Palaeocene, is a geological epoch (geology), epoch that lasted from about 66 to 56 mya (unit), million years ago (mya). It is the first epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), E ...
epoch ( 66 to 56 Ma ago, after the
Cretaceous–Paleogene extinction event
The Cretaceous–Paleogene (K–Pg) extinction event (also known as the Cretaceous–Tertiary extinction) was a sudden mass extinction of three-quarters of the plant and animal species on Earth, approximately 66 million years ago. With the ...
). The oldest preserved descriptions of snakes can be found in the
Brooklyn Papyrus
The Brooklyn Papyrus (''47.218.48'' and ''47.218.85'', also known as the Brooklyn Medical Papyrus) is a medical papyrus dating from ancient Egypt and is one of the oldest preserved writings about medicine and ophiology. The manuscript is dated ...
.
Most species of snake are nonvenomous and
those that have venom use it primarily to kill and subdue prey rather than for self-defense. Some possess venom that is potent enough to cause painful injury or death to humans. Nonvenomous snakes either swallow prey alive or kill by
constriction
Constriction is a method used by various snake species to kill or subdue their prey. Although some species of venomous and mildly venomous snakes do use constriction to subdue their prey, most snakes which use constriction lack venom. The snake i ...
.
Etymology
The English word ''snake'' comes from
Old English
Old English (, ), or Anglo-Saxon, is the earliest recorded form of the English language, spoken in England and southern and eastern Scotland in the early Middle Ages. It was brought to Great Britain by Anglo-Saxon settlement of Britain, Anglo ...
, itself from
Proto-Germanic
Proto-Germanic (abbreviated PGmc; also called Common Germanic) is the reconstructed proto-language of the Germanic branch of the Indo-European languages.
Proto-Germanic eventually developed from pre-Proto-Germanic into three Germanic branc ...
(
cf. Germanic 'ring snake', Swedish 'grass snake'), from
Proto-Indo-European
Proto-Indo-European (PIE) is the reconstructed common ancestor of the Indo-European language family. Its proposed features have been derived by linguistic reconstruction from documented Indo-European languages. No direct record of Proto-Indo-E ...
root 'to crawl to creep', which also gave ''sneak'' as well as
Sanskrit
Sanskrit (; attributively , ; nominally , , ) is a classical language belonging to the Indo-Aryan branch of the Indo-European languages. It arose in South Asia after its predecessor languages had diffused there from the northwest in the late ...
'snake'. The word ousted ''
adder
Adder may refer to:
* AA-12 Adder, a Russian air-to-air missile
* Adder (electronics), an electronic circuit designed to do addition
* Adder Technology, a manufacturing company
* Armstrong Siddeley Adder, a late 1940s British turbojet engine
* ''B ...
'', as ''adder'' went on to narrow in meaning, though in Old English was the general word for snake. The other term, ''serpent'', is from French, ultimately from Indo-European 'to creep',
which also gave
Ancient Greek
Ancient Greek includes the forms of the Greek language used in ancient Greece and the ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Dark Ages (), the Archaic peri ...
() 'I crawl'.
Evolution
The fossil record of snakes is relatively poor because snake
skeleton
A skeleton is the structural frame that supports the body of an animal. There are several types of skeletons, including the exoskeleton, which is the stable outer shell of an organism, the endoskeleton, which forms the support structure inside ...
s are typically small and fragile making
fossil
A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...
ization uncommon. Fossils readily identifiable as snakes (though often retaining hind limbs) first appear in the fossil record during the
Cretaceous
The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of th ...
period. The earliest known true snake fossils (members of the crown group Serpentes) come from the marine
simoliophiids, the oldest of which is the
Late Cretaceous
The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''creta'', the ...
(
Cenomanian
The Cenomanian is, in the ICS' geological timescale, the oldest or earliest age of the Late Cretaceous Epoch or the lowest stage of the Upper Cretaceous Series. An age is a unit of geochronology; it is a unit of time; the stage is a unit in the s ...
age) ''
Haasiophis terrasanctus
''Haasiophis'', consisting of the sole species ''Haasiophis terrasanctus'', is an extinct genus of snakes with hind limbs. It is one of three genera of Cenomanian snakes known to have possessed hindlimbs.
Etymology
The genus was named in honor ...
'',
dated to between 112 and 94 million years old.
Based on
comparative anatomy
Comparative anatomy is the study of similarities and differences in the anatomy of different species. It is closely related to evolutionary biology and phylogeny (the evolution of species).
The science began in the classical era, continuing in t ...
, there is consensus that snakes descended from
lizard
Lizards are a widespread group of squamate reptiles, with over 7,000 species, ranging across all continents except Antarctica, as well as most oceanic island chains. The group is paraphyletic since it excludes the snakes and Amphisbaenia alt ...
s.
Python
Python may refer to:
Snakes
* Pythonidae, a family of nonvenomous snakes found in Africa, Asia, and Australia
** ''Python'' (genus), a genus of Pythonidae found in Africa and Asia
* Python (mythology), a mythical serpent
Computing
* Python (pro ...
s and
boa
Kwon Bo-ah (; born November 5, 1986), known professionally as BoA, is a South Korean singer, songwriter, dancer, record producer and actress. One of the most successful and influential Korean entertainers, she has been dubbed the " Queen of K- ...
s—primitive groups among modern snakes—have vestigial hind limbs: tiny, clawed digits known as
anal spur
Anal may refer to:
Related to the anus
*Related to the anus of animals:
** Anal fin, in fish anatomy
** Anal vein, in insect anatomy
** Anal scale, in reptile anatomy
*Related to the human anus:
** Anal sex, a type of sexual activity involving s ...
s, which are used to grasp during mating.
The families
Leptotyphlopidae and
Typhlopidae
The Typhlopidae are a family of blind snakes. They are found mostly in the tropical regions of Africa, Asia, the Americas, and all mainland Australia and various islands. The rostral scale overhangs the mouth to form a shovel-like burrowing str ...
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
An atlas is a collection of maps; it is typically a bundle of maps of Earth or of a region of Earth.
Atlases have traditionally been bound into book form, but today many atlases are in multimedia formats. In addition to presenting geographic ...
,
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.
Many modern snake groups originated during the
Paleocene
The Paleocene, ( ) or Palaeocene, is a geological epoch (geology), epoch that lasted from about 66 to 56 mya (unit), million years ago (mya). It is the first epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), E ...
, alongside the
adaptive radiation
In evolutionary biology, adaptive radiation is a process in which organisms diversify rapidly from an ancestral species into a multitude of new forms, particularly when a change in the environment makes new resources available, alters biotic int ...
of mammals following the extinction of (non-avian)
dinosaur
Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...
s. 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
viper
The Viperidae (vipers) are a family of snakes found in most parts of the world, except for Antarctica, Australia, Hawaii, Madagascar, and various other isolated islands. They are venomous and have long (relative to non-vipers), hinged fangs tha ...
s and
elapids in North America and the significant diversification of
Colubridae
Colubridae (, commonly known as colubrids , from la, coluber, 'snake') is a family of snakes. With 249 genera, it is the largest snake family. The earliest species of the family date back to the Oligocene epoch. Colubrid snakes are found on ever ...
(including the origin of many modern genera such as
Nerodia,
Lampropeltis,
Pituophis
''Pituophis'' is a genus of nonvenomous colubrid snakes, commonly referred to as gopher snakes, pine snakes, and bullsnakes, which are endemic to North America.
Geographic range
Species and subspecies within the genus ''Pituophis'' are found ...
, and
Pantherophis
''Pantherophis'' is a genus of nonvenomous colubrid snakes endemic to central and eastern regions of North America. It consists of the North American ratsnakes, the foxsnakes, and the cornsnakes. The genus, which contains 10 recognized specie ...
).
Fossils
There is fossil evidence to suggest that snakes may have evolved from burrowing lizards, during the
Cretaceous Period.
An early fossil snake relative, ''
Najash rionegrina
''Najash'' is an extinct genus of basal snake from the Late Cretaceous Candeleros Formation of Patagonia. Like a number of other Cretaceous and living snakes it retained hindlimbs, but ''Najash'' is unusual in having well-developed legs that ...
'', was a two-legged burrowing animal with a
sacrum
The sacrum (plural: ''sacra'' or ''sacrums''), in human anatomy, is a large, triangular bone at the base of the spine that forms by the fusing of the sacral vertebrae (S1S5) between ages 18 and 30.
The sacrum situates at the upper, back part ...
, and was fully
terrestrial.
One
extant
Extant is the opposite of the word extinct. It may refer to:
* Extant hereditary titles
* Extant literature, surviving literature, such as ''Beowulf'', the oldest extant manuscript written in English
* Extant taxon, a taxon which is not extinct, ...
analog of these putative ancestors is the earless monitor ''
Lanthanotus'' of
Borneo
Borneo (; id, Kalimantan) is the third-largest island in the world and the largest in Asia. At the geographic centre of Maritime Southeast Asia, in relation to major Indonesian islands, it is located north of Java, west of Sulawesi, and eas ...
(though it also is
semiaquatic).
Subterranean
Subterranean(s) or The Subterranean(s) may refer to:
* Subterranea (geography), underground structures, both natural and man-made
Literature
* ''Subterranean'' (novel), a 1998 novel by James Rollins
* ''Subterranean Magazine'', an American fa ...
species evolved bodies streamlined for burrowing, and eventually lost their limbs.
According to this hypothesis, features such as the
transparent, fused eyelids (
brille
The brille (also called the ocular scale, eye cap or spectacle) is the layer of transparent, immovable disc-shaped skin or scale covering the eyes of some animals for protection, especially in animals without eyelids. The brille has evolved fro ...
) and loss of external ears evolved to cope with
fossorial
A fossorial () animal is one adapted to digging which lives primarily, but not solely, underground. Some examples are badgers, naked mole-rats, clams, meerkats, and mole salamanders, as well as many beetles, wasps, and bees.
Prehistoric eviden ...
difficulties, such as scratched
cornea
The cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber. Along with the anterior chamber and lens, the cornea refracts light, accounting for approximately two-thirds of the eye's total optical power ...
s 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
''Pachyrhachis'' (from el, παχύς , 'thick' and el, ῥάχῐς , 'spine') is an extinct genus of snake with well developed hind legs known from fossils discovered in Ein Yabrud, near Ramallah, in the central West Bank. It is a relatively ...
'' and ''
Eupodophis'', which are slightly older than ''
Najash''.
[
]
This hypothesis was strengthened in 2015 by the discovery of a 113-million-year-old fossil of a four-legged snake in Brazil that has been named ''
Tetrapodophis 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. A study in 2021 places the animal in a group of extinct marine lizards from the Cretaceous period known as
dolichosaur
''Dolichosaurus'' (meaning "long lizard") is an extinct genus of marine squamate of the Upper Cretaceous Cenomanian chalk deposits of England. Sister-group relationships between coniasaurs, dolichosaurs, Aigialosauridae and Mosasauridae are ...
s and not directly related to snakes.
An alternative hypothesis, based on
morphology
Morphology, from the Greek and meaning "study of shape", may refer to:
Disciplines
*Morphology (archaeology), study of the shapes or forms of artifacts
*Morphology (astronomy), study of the shape of astronomical objects such as nebulae, galaxies, ...
, suggests the ancestors of snakes were related to
mosasaur
Mosasaurs (from Latin ''Mosa'' meaning the 'Meuse', and Greek ' meaning 'lizard') comprise a group of extinct, large marine reptiles from the Late Cretaceous. Their first fossil remains were discovered in a limestone quarry at Maastricht on th ...
s—extinct
aquatic reptiles from the
Cretaceous
The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of th ...
—forming the clade
Pythonomorpha
Pythonomorpha was originally proposed by paleontologist Edward Drinker Cope (1869) as a reptilian order comprising mosasaurs, which he believed to be close relatives of Ophidia (snakes). The etymology of the term Pythonomorpha comes from the Greek ...
.
According to this hypothesis, the fused, transparent eyelids of snakes are thought to have evolved to combat marine conditions (corneal water loss through osmosis), and the external ears were lost through disuse in an aquatic environment. This ultimately led to an animal similar to today's
sea snake
Sea snakes, or coral reef snakes, are elapid snakes that inhabit marine environments for most or all of their lives. They belong to two subfamilies, Hydrophiinae and Laticaudinae. Hydrophiinae also includes Australasian terrestrial snakes, wher ...
s. In the Late
Cretaceous
The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of th ...
, 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
Cladistics (; ) is an approach to biological classification in which organisms are categorized in groups (" clades") based on hypotheses of most recent common ancestry. The evidence for hypothesized relationships is typically shared derived cha ...
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
The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The J ...
and Early Cretaceous indicate deeper fossil records for these groups, which may potentially refute either hypothesis.
File:Tetrapodophis amplectus 3483.jpg, '' Tetrapodophis''
File:Eupodophis at Royal Belgian Institute of Natural Sciences, Brussels.jpg, ''Eupodophis descouensi
''Eupodophis'' is an extinct genus of snake from the Late Cretaceous period. It has two small hind legs and is considered a transitional form between Cretaceous lizards and limbless snakes. The feature, described as vestigial, was most likely us ...
''
File:Eupodophis descouensi Holotype.jpg, ''Eupodophis descouensi
''Eupodophis'' is an extinct genus of snake from the Late Cretaceous period. It has two small hind legs and is considered a transitional form between Cretaceous lizards and limbless snakes. The feature, described as vestigial, was most likely us ...
''
File:Eupodophis descouensi Holotype hind leg.jpg, '' Eupodophis descouensi'' hind leg
Genetic basis of snake evolution
Both fossils and
phylogenetic
In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...
studies demonstrate that snakes evolved from
lizard
Lizards are a widespread group of squamate reptiles, with over 7,000 species, ranging across all continents except Antarctica, as well as most oceanic island chains. The group is paraphyletic since it excludes the snakes and Amphisbaenia alt ...
s, hence the question became which genetic changes led to limb loss in the snake ancestor. Limb loss is actually very common in extant reptiles and has happened dozens of times within
skink
Skinks are lizards belonging to the family Scincidae, a family in the infraorder Scincomorpha. With more than 1,500 described species across 100 different taxonomic genera, the family Scincidae is one of the most diverse families of lizards. Ski ...
s,
anguids, and other lizards.
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
Sonic hedgehog protein (SHH) is encoded for by the ''SHH'' gene. The protein is named after the character ''Sonic the Hedgehog''.
This signaling molecule is key in regulating embryonic morphogenesis in all animals. SHH controls organogenesis and ...
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.
Distribution
![World distribution of snakes](https://upload.wikimedia.org/wikipedia/commons/d/d4/World_distribution_of_snakes.svg)
There are about 3,900 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, as well as in the sea, and as high as in the
Himalayan Mountains
The Himalayas, or Himalaya (; ; ), is a mountain range in Asia, separating the plains of the Indian subcontinent from the Tibetan Plateau. The range has some of the planet's highest peaks, including the very highest, Mount Everest. Over 100 ...
of Asia.
There are numerous islands from which snakes are absent, such as
Ireland
Ireland ( ; ga, Éire ; Ulster Scots dialect, Ulster-Scots: ) is an island in the Atlantic Ocean, North Atlantic Ocean, in Northwestern Europe, north-western Europe. It is separated from Great Britain to its east by the North Channel (Grea ...
,
Iceland
Iceland ( is, Ísland; ) is a Nordic island country in the North Atlantic Ocean and in the Arctic Ocean. Iceland is the most sparsely populated country in Europe. Iceland's capital and largest city is Reykjavík, which (along with its s ...
, and
New Zealand
New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and over 700 smaller islands. It is the sixth-largest island count ...
(although New Zealand's waters are infrequently visited by the yellow-bellied sea snake
The yellow-bellied sea snake (''Hydrophis platurus'') is a venomous species of snake from the subfamily Hydrophiinae (the sea snakes) found in tropical oceanic waters around the world except for the Atlantic Ocean. For many years, it was place ...
and the banded sea krait
The yellow-lipped sea krait (''Laticauda colubrina''), also known as the banded sea krait or colubrine sea krait, is a species of venomous sea snake found in tropical Indo-Pacific oceanic waters. The snake has distinctive black stripes and a ye ...
).
Taxonomy
All modern snakes are grouped within the suborder
Order ( la, ordo) is one of the eight major hierarchical taxonomic ranks in Linnaean taxonomy. It is classified between family and class. In biological classification, the order is a taxonomic rank used in the classification of organisms and ...
Serpentes in Linnean taxonomy, part of the order
Order, ORDER or Orders may refer to:
* Categorization, the process in which ideas and objects are recognized, differentiated, and understood
* Heterarchy, a system of organization wherein the elements have the potential to be ranked a number of d ...
Squamata
Squamata (, Latin ''squamatus'', 'scaly, having scales') is the largest order of reptiles, comprising lizards, snakes, and amphisbaenians (worm lizards), which are collectively known as squamates or scaled reptiles. With over 10,900 species, ...
, though their precise placement within squamates remains controversial.
The two infraorders of Serpentes are: Alethinophidia
:''Common names: advanced snakes.''
The Alethinophidia are an infraorder of snakes that includes all snakes other than blind snakes and thread snakes. Snakes have long been grouped into families within Alethinophidia based on their morphology, e ...
and Scolecophidia. This separation is based on morphological characteristics and mitochondrial DNA
Mitochondrial DNA (mtDNA or mDNA) is the DNA located in mitochondria, cellular organelles within eukaryotic cells that convert chemical energy from food into a form that cells can use, such as adenosine triphosphate (ATP). Mitochondrial D ...
sequence similarity. Alethinophidia is sometimes split into Henophidia
Henophidia is a former superfamily of the suborder Serpentes (snakes) that contains boas, pythons and numerous other less-well-known snakes.
Snakes once considered to belong to superfamily Henophidia include two families now considered Ameroph ...
and Caenophidia
The Caenophidia are a derived clade of alethinophidian snakes, which contains over 80% of all the extant species of snakes. The largest family is Colubridae, but it also includes at least seven other families, at least four of which were once ...
, 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
''Wonambi'' is an extinct genus of madtsoiid snakes that lived in late Neogene to late Quaternary Australia. Species of ''Wonambi'' were constrictor snakes unrelated to Australian pythons.
Description
''Wonambi'' was a fairly large snake, ...
''.
There are numerous debates in the systematics within the group. For instance, many sources classify Boidae and Pythonidae
The Pythonidae, commonly known as pythons, are a family of nonvenomous snakes found in Africa, Asia, and Australia. Among its members are some of the largest snakes in the world. Ten genera and 42 species are currently recognized.
Distributi ...
as one family, while some keep the Elapidae and Hydrophiidae
Hydrophiinae is a subfamily of venomous snakes in the family Elapidae. It contains most sea snakes and many genera of venomous land snakes found in Australasia, such as the taipans (''Oxyuranus''), tiger snakes (''Notechis''), Pseudonaja, brown sn ...
(sea snakes) separate for practical reasons despite their extremely close relation.
Recent molecular studies support the monophyly
In cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population) and all of its lineal descendants. Monophyletic grou ...
of the clades
A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, t ...
of modern snakes, scolecophidians, typhlopids + anomalepidids, alethinophidians, core alethinophidians, uropeltids (''Cylindrophis'', ''Anomochilus'', uropeltines), macrostomatans, booids, boids, pythonids and caenophidians.
Families
Legless lizards
While snakes are limbless reptiles, evolved from (and grouped with) lizards, there are many other species of lizards that have lost their limbs independently but which superficially look similar to snakes. These include the slowworm and glass snake.
Other serpentine tetrapods that are unrelated to snakes include caecilians (amphibians), amphisbaenia
Amphisbaenia (called amphisbaenians or worm lizards) is a group of usually legless squamates, comprising over 200 extant species. Amphisbaenians are characterized by their long bodies, the reduction or loss of the limbs, and rudimentary eyes. As ...
ns (near-lizard squamates), and the extinct aistopods
Aistopoda (Greek for " avingnot-visible feet") is an order of highly specialised snake-like stegocephalians known from the Carboniferous and Early Permian of Europe and North America, ranging from tiny forms only , to nearly in length. They fi ...
(amphibians).
Biology
Size
The now extinct
Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...
'' Titanoboa cerrejonensis'' was in length. By comparison, the largest extant
Extant is the opposite of the word extinct. It may refer to:
* Extant hereditary titles
* Extant literature, surviving literature, such as ''Beowulf'', the oldest extant manuscript written in English
* Extant taxon, a taxon which is not extinct, ...
snakes are the reticulated python
The reticulated python (''Malayopython reticulatus'') is a python species native to South and Southeast Asia. It is the world's longest snake, and is among the three heaviest. It is listed as least concern on the IUCN Red List because of its wi ...
, measuring about long, and the green anaconda
The green anaconda (''Eunectes murinus''), also known as the giant Emerald anaconda, common anaconda, common water boa or sucuri, is a boa species found in South America. It is the heaviest and one of the longest known extant snake species. Lik ...
, which measures about long and is considered the heaviest snake on Earth at .
At the other end of the scale, the smallest extant snake is ''Leptotyphlops carlae
The Barbados threadsnake (''Tetracheilostoma carlae'') is a species of threadsnake. It is the smallest known snake species. This member of the Leptotyphlopidae family is found on the Caribbean islands of Barbados and Anguilla.
Taxonomy and et ...
'', with a length of about . Most snakes are fairly small animals, approximately in length.
Perception
Pit vipers, pythons, and some boas have infrared-sensitive receptors in deep grooves on the snout, allowing 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.
A snake tracks its prey using smell, collecting airborne particles with its forked tongue, then passing them to the vomeronasal organ
The vomeronasal organ (VNO), or Jacobson's organ, is the paired auxiliary olfactory (smell) sense organ located in the soft tissue of the nasal septum, in the nasal cavity just above the roof of the mouth (the hard palate) in various tetrapods. ...
or ''Jacobson's organ'' in the mouth for examination. The fork in the tongue provides a sort of directional sense of smell and taste simultaneously. The snake's tongue is 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
Anacondas or water boas are a group of large snakes of the genus ''Eunectes''. They are found in tropical South America. Four species are currently recognized.
Description
Although the name applies to a group of snakes, it is often used to re ...
, the tongue functions efficiently underwater.
The underside of a snake is very sensitive to vibration, allowing the snake to detect approaching animals by sensing faint vibrations in the ground.
Snake vision varies greatly between species. Some have keen eyesight and others are only able to distinguish light from dark, but the important trend is that a snake's visual perception is adequate enough to track movements. Generally, vision is best in tree-dwelling snakes and weakest in burrowing snakes. Some have binocular vision, where both eyes are capable of focusing on the same point, an example of this being the Asian vine snake. Most snakes focus by moving the lens back and forth in relation to the retina
The retina (from la, rete "net") is the innermost, light-sensitive layer of tissue of the eye of most vertebrates and some molluscs. The optics of the eye create a focused two-dimensional image of the visual world on the retina, which then ...
. Diurnal snakes have round pupils and many nocturnal snakes have slit pupils. Most species possess three visual pigments and are probably able to see two primary colors in daylight. It has been concluded that the last common ancestors of all snakes had UV-sensitive vision, but most snakes that depend on their eyesight to hunt in daylight have evolved lenses that act like sunglasses for filtering out the UV-light, which probably also sharpens their vision by improving the contrast.
Skin
The skin of a snake is covered in scales
Scale or scales may refer to:
Mathematics
* Scale (descriptive set theory), an object defined on a set of points
* Scale (ratio), the ratio of a linear dimension of a model to the corresponding dimension of the original
* Scale factor, a number w ...
. Contrary to the popular notion of snakes being slimy (because of possible confusion of snakes with worm
Worms are many different distantly related bilateral animals that typically have a long cylindrical tube-like body, no limbs, and no eyes (though not always).
Worms vary in size from microscopic to over in length for marine polychaete wor ...
s), snakeskin has a smooth, dry texture. Most snakes use specialized belly scales to travel, allowing them to grip surfaces. The body scales may be smooth, keeled, or granular. The eyelids of a snake are transparent "spectacle" scales, also known as brille
The brille (also called the ocular scale, eye cap or spectacle) is the layer of transparent, immovable disc-shaped skin or scale covering the eyes of some animals for protection, especially in animals without eyelids. The brille has evolved fro ...
, which remain permanently closed.
The shedding of scales is called ''ecdysis
Ecdysis is the moulting of the cuticle in many invertebrates of the clade Ecdysozoa. Since the cuticle of these animals typically forms a largely inelastic exoskeleton, it is shed during growth and a new, larger covering is formed. The remna ...
'' (or in normal usage, ''molting'' or ''sloughing''). Snakes shed the complete outer layer of skin in one piece.[Smith, Malcolm A. '']The Fauna of British India, Including Ceylon and Burma
''The Fauna of British India'' (short title) with long titles including ''The Fauna of British India, Including Ceylon and Burma'', and ''The Fauna of British India Including the Remainder of the Oriental Region'' is a series of scientific books th ...
''. Vol I, Loricata and Testudines. p. 30. Snake scales are not discrete, but extensions of the epidermis
The epidermis is the outermost of the three layers that comprise the skin, the inner layers being the dermis and hypodermis. The epidermis layer provides a barrier to infection from environmental pathogens and regulates the amount of water rele ...
—hence they are not shed separately but as a complete outer layer during each molt, akin to a sock being turned inside out.
Snakes have a wide diversity of skin coloration patterns which are often related to behavior, such as the tendency to have to flee from predators. Snakes that are at a high risk of predation tend to be plain, or have longitudinal stripes, providing few reference points to predators, thus allowing the snake to escape without being noticed. Plain snakes usually adopt active hunting strategies, as their pattern allows them to send little information to prey about motion. Blotched snakes usually use ambush-based strategies, likely because it helps them blend into an environment with irregularly shaped objects, like sticks or rocks. Spotted patterning can similarly help snakes to blend into their environment.
The shape and number of scales on the head, back, and belly are often characteristic and used for taxonomic purposes. Scales are named mainly according to their positions on the body. In "advanced" (Caenophidia
The Caenophidia are a derived clade of alethinophidian snakes, which contains over 80% of all the extant species of snakes. The largest family is Colubridae, but it also includes at least seven other families, at least four of which were once ...
n) snakes, the broad belly scales and rows of dorsal scale
In snakes, the dorsal scales are the longitudinal series of plates that encircle the body, but do not include the ventral scales. Campbell JA, Lamar WW (2004). ''The Venomous Reptiles of the Western Hemisphere''. Ithaca and London: Comstock Publis ...
s correspond to the vertebra
The spinal column, a defining synapomorphy shared by nearly all vertebrates,Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristic ...
e, allowing these to be counted without the need for dissection
Dissection (from Latin ' "to cut to pieces"; also called anatomization) is the dismembering of the body of a deceased animal or plant to study its anatomical structure. Autopsy is used in pathology and forensic medicine to determine the cause o ...
.
Molting
Molting
In biology, moulting (British English), or molting (American English), also known as sloughing, shedding, or in many invertebrates, ecdysis, is the manner in which an animal routinely casts off a part of its body (often, but not always, an outer ...
(or "ecdysis") serves a number of purposes. It allows old, worn skin to be replaced and it can remove parasites such as mite
Mites are small arachnids (eight-legged arthropods). Mites span two large orders of arachnids, the Acariformes and the Parasitiformes, which were historically grouped together in the subclass Acari, but genetic analysis does not show clear evid ...
s and tick
Ticks (order Ixodida) are parasitic arachnids that are part of the mite superorder Parasitiformes. Adult ticks are approximately 3 to 5 mm in length depending on age, sex, species, and "fullness". Ticks are external parasites, living by ...
s that live in the skin. It's also been observed in snakes that molting can be synced to mating cycles. Shedding skin can release pheromones and revitalize color and patterns of the skin to increase attraction of mates. Renewal of the skin by molting supposedly allows growth in some animals such as insects, but this has been disputed in the case of snakes.
Molting occurs periodically throughout the life of a snake. Before each 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 snake's eyes turn cloudy or blue-colored. The inner surface of the old skin liquefies, causing it to separate from the new skin beneath it. After a few days, the eyes become clear and the snake "crawls" out of its old skin, which splits close to the snake's mouth. The snake rubs its body against rough surfaces to aid in the shedding of its old skin. 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, revealing a new, larger, brighter layer of skin which has formed underneath.
A young snake that is still growing may shed its skin up to four times a year, but an older snake may shed only once or twice a year. The discarded skin carries a perfect imprint of the scale pattern, so it is usually possible to identify the snake from the cast skin if it is reasonably intact. This periodic renewal has led to the snake being a symbol of healing
With physical trauma or disease suffered by an organism, healing involves the repairing of damaged tissue(s), organs and the biological system as a whole and resumption of (normal) functioning. Medicine includes the process by which the cells i ...
and medicine
Medicine is the science and practice of caring for a patient, managing the diagnosis, prognosis, prevention, treatment, palliation of their injury or disease, and promoting their health. Medicine encompasses a variety of health care pract ...
, as pictured in the Rod of Asclepius
In Greek mythology, the Rod of Asclepius (⚕; grc, Ράβδος του Ασκληπιού, , sometimes also spelled Asklepios), also known as the Staff of Aesculapius and as the asklepian, is a serpent-entwined rod wielded by the Greek god A ...
.
Scale counts can sometimes be used to identify the sex of a snake when the species is not distinctly sexually dimorphic. A probe is fully inserted into the cloaca
In animal anatomy, a cloaca ( ), plural cloacae ( or ), is the posterior orifice that serves as the only opening for the digestive, reproductive, and urinary tracts (if present) of many vertebrate animals. All amphibians, reptiles and birds, a ...
, marked at the point where it stops, then removed and measured against the subcaudal scales
In snakes, the subcaudal scales are the enlarged plates on the underside of the tail.Wright AH, Wright AA. 1957. Handbook of Snakes. Comstock Publishing Associates (7th printing, 1985). 1105 pp. . These scales may be either single or divided (pair ...
.[Rosenfeld (1989), p. 11.] The scalation count determines whether the snake is a male or female, as the hemipenes
A hemipenis (plural hemipenes) is one of a pair of intromittent organs of male squamata, squamates (snakes, lizards and amphisbaenia, worm lizards). Hemipenes are usually held inverted within the body, and are everted for reproduction via erecti ...
of a male will probe to a different depth (usually longer) than the cloaca of a female.
Skeleton
The skeleton
A skeleton is the structural frame that supports the body of an animal. There are several types of skeletons, including the exoskeleton, which is the stable outer shell of an organism, the endoskeleton, which forms the support structure inside ...
of most snakes consists solely of the skull, hyoid, vertebral column, and ribs, though henophidia
Henophidia is a former superfamily of the suborder Serpentes (snakes) that contains boas, pythons and numerous other less-well-known snakes.
Snakes once considered to belong to superfamily Henophidia include two families now considered Ameroph ...
n snakes retain vestiges of the pelvis and rear limbs.
The skull 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, and the posterior end of the lower jaw bones articulate with a quadrate bone, allowing further mobility. The mandible
In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower tooth, teeth in place. The mandible sits beneath the maxilla. It is the only movabl ...
and quadrate bones can pick up ground-borne vibrations; because the sides of the lower jaw can move independently of one another, a snake resting its jaw on a surface has sensitive stereo auditory perception
Hearing, or auditory perception, is the ability to perceive sounds through an organ, such as an ear, by detecting vibrations as periodic changes in the pressure of a surrounding medium. The academic field concerned with hearing is auditory ...
, used for detecting the position of prey. The jaw–quadrate– stapes pathway is capable of detecting vibrations on the angstrom
The angstromEntry "angstrom" in the Oxford online dictionary. Retrieved on 2019-03-02 from https://en.oxforddictionaries.com/definition/angstrom.Entry "angstrom" in the Merriam-Webster online dictionary. Retrieved on 2019-03-02 from https://www.m ...
scale, despite the absence of an outer ear and the lack of an impedance matching mechanism—provided by the ossicles
The ossicles (also called auditory ossicles) are three bones in either middle ear that are among the smallest bones in the human body. They serve to transmit sounds from the air to the fluid-filled labyrinth (cochlea). The absence of the auditory ...
in other vertebrates—for receiving 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 the muscles of the snake's tongue, as it does in all other tetrapod
Tetrapods (; ) are four-limbed vertebrate animals constituting the superclass Tetrapoda (). It includes extant and extinct amphibians, sauropsids ( reptiles, including dinosaurs and therefore birds) and synapsids (pelycosaurs, extinct theraps ...
s.
The vertebral column consists of between 200 and 400 vertebrae, or sometimes more. The body vertebrae each have two ribs articulating with them. The tail vertebrae are comparatively few in number (often less than 20% of the total) and lack ribs. The vertebrae have projections that allow for strong muscle attachment, enabling locomotion without limbs.
Caudal autotomy
Autotomy (from the Greek language, Greek ''auto-'', "self-" and ''tome'', "severing", wikt:αὐτοτομία, αὐτοτομία) or self-amputation, is the behaviour whereby an animal sheds or discards one or more of its own appendages, usual ...
(self-amputation of the tail), a feature found in some lizards, is absent in most snakes. In the rare cases where it does exist in snakes, caudal autotomy is intervertebral (meaning the separation of adjacent vertebrae), unlike that in lizards, which is intravertebral, i.e. the break happens along a predefined fracture plane present on a vertebra.
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 polyphyodont
A polyphyodont is any animal whose teeth are continually replaced. In contrast, diphyodonts are characterized by having only two successive sets of teeth.
Polyphyodonts include most toothed fishes, many reptiles such as crocodiles and geckos, and ...
s with teeth that are continuously replaced.
Internal organs
Snakes and other non-archosaur
Archosauria () is a clade of diapsids, with birds and crocodilians as the only living representatives. Archosaurs are broadly classified as reptiles, in the cladistic sense of the term which includes birds. Extinct archosaurs include non-avian d ...
(crocodilia
Crocodilia (or Crocodylia, both ) is an order of mostly large, predatory, semiaquatic reptiles, known as crocodilians. They first appeared 95 million years ago in the Late Cretaceous period ( Cenomanian stage) and are the closest living ...
ns, dinosaur
Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...
s + bird
Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweigh ...
s and allies) reptiles have a three-chambered heart that controls the circulatory system
The blood circulatory system is a system of organs that includes the heart, blood vessels, and blood which is circulated throughout the entire body of a human or other vertebrate. It includes the cardiovascular system, or vascular system, tha ...
via the left and right atrium, and one ventricle. Internally, the ventricle is divided into three interconnected cavities: the cavum arteriosum, the cavum pulmonale, and the cavum venosum. The cavum venosum receives deoxygenated blood
Blood is a body fluid in the circulatory system of humans and other vertebrates that delivers necessary substances such as nutrients and oxygen to the cells, and transports metabolic waste products away from those same cells. Blood in the c ...
from the right atrium and the cavum arteriosum receives oxygenated blood from the left atrium. Located beneath the cavum venosum is the cavum pulmonale, which pumps blood to the pulmonary trunk.
The snake's heart is encased in a sac, called the ''pericardium
The pericardium, also called pericardial sac, is a double-walled sac containing the heart and the roots of the great vessels. It has two layers, an outer layer made of strong connective tissue (fibrous pericardium), and an inner layer made of ...
'', located at the bifurcation of the bronchi. The heart is able to move around, owing to the lack of a diaphragm; this adjustment protects the heart from potential damage when large ingested prey is passed through the esophagus
The esophagus (American English) or oesophagus (British English; both ), non-technically known also as the food pipe or gullet, is an organ in vertebrates through which food passes, aided by peristaltic contractions, from the pharynx to the ...
. The spleen
The spleen is an organ found in almost all vertebrates. Similar in structure to a large lymph node, it acts primarily as a blood filter. The word spleen comes . is attached to the gall bladder and pancreas
The pancreas is an organ of the digestive system and endocrine system of vertebrates. In humans, it is located in the abdomen behind the stomach and functions as a gland. The pancreas is a mixed or heterocrine gland, i.e. it has both an end ...
and filters the blood. The thymus
The thymus is a specialized primary lymphoid organ of the immune system. Within the thymus, thymus cell lymphocytes or ''T cells'' mature. T cells are critical to the adaptive immune system, where the body adapts to specific foreign invaders. ...
, located in fatty tissue above the heart, is responsible for the generation of immune cells in the blood. The cardiovascular system of snakes is unique for the presence of a renal portal system in which the blood from the snake's tail passes through the kidneys before returning to the heart.
The vestigial
Vestigiality is the retention, during the process of evolution, of genetically determined structures or attributes that have lost some or all of the ancestral function in a given species. Assessment of the vestigiality must generally rely on co ...
left lung
The lungs are the primary organs of the respiratory system in humans and most other animals, including some snails and a small number of fish. In mammals and most other vertebrates, two lungs are located near the backbone on either side of t ...
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
Fluid statics or hydrostatics is the branch of fluid mechanics that studies the condition of the equilibrium of a floating body and submerged body "fluids at hydrostatic equilibrium and the pressure in a fluid, or exerted by a fluid, on an imme ...
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, one located ahead of the other.
Snakes have no lymph node
A lymph node, or lymph gland, is a kidney-shaped organ of the lymphatic system and the adaptive immune system. A large number of lymph nodes are linked throughout the body by the lymphatic vessels. They are major sites of lymphocytes that inclu ...
s.
Venom
Cobras, vipers, and closely related species use venom
Venom or zootoxin is a type of toxin produced by an animal that is actively delivered through a wound by means of a bite, sting, or similar action. The toxin is delivered through a specially evolved ''venom apparatus'', such as fangs or a sti ...
to immobilize, injure, or kill their prey. The venom is modified saliva
Saliva (commonly referred to as spit) is an extracellular fluid produced and secreted by salivary glands in the mouth. In humans, saliva is around 99% water, plus electrolytes, mucus, white blood cells, epithelial cells (from which DNA can be ...
, delivered through fangs
A fang is a long, pointed tooth. In mammals, a fang is a modified maxillary tooth, used for biting and tearing flesh. In snakes, it is a specialized tooth that is associated with a venom gland (see snake venom). Spiders also have external fangs ...
. The fangs of 'advanced' venomous snakes like viperids and elapids are hollow, allowing venom to be injected more effectively, and the fangs of rear-fanged
A snake skeleton consists primarily of the skull, vertebrae, and ribs, with only vestigial remnants of the limbs.
Skull
The skull of a snake is a very complex structure, with numerous joints to allow the snake to swallow prey far larger than i ...
snakes such as the boomslang simply have a groove on the posterior edge to channel venom into the wound. Snake venoms are often prey-specific, and their role in self-defense is secondary.
Venom, like all salivary secretions, is a predigestant that initiates the breakdown of food into soluble compounds, facilitating proper digestion. Even nonvenomous snakebites (like any animal bite) cause tissue damage.
Certain birds, mammals, and other snakes (such as kingsnake
Kingsnakes are Colubridae, colubrid New World members of the genus ''Lampropeltis'', which includes 26 species. Among these, about 45 subspecies are recognized. They are nonvenomous and ophiophagy, ophiophagous in diet.
Description
Kingsnakes ...
s) that prey on venomous snakes have developed resistance and even immunity to certain venoms. Venomous snakes include three families
Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Ideall ...
of snakes, and do not constitute a formal taxonomic classification group.
The colloquial
Colloquialism (), also called colloquial language, everyday language or general parlance, is the linguistic style used for casual (informal) communication. It is the most common functional style of speech, the idiom normally employed in conver ...
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, two exceptions: '' Rhabdophis'' sequesters toxins from the toads it eats, then secretes them from nuchal glands to ward off predators; and a small unusual population of garter snake
Garter snake is a common name for generally harmless, small to medium-sized snakes belonging to the genus ''Thamnophis'' in the family Colubridae. Native to North and Central America, species in the genus ''Thamnophis'' can be found from the sub ...
s in the US state of Oregon
Oregon () is a U.S. state, state in the Pacific Northwest region of the Western United States. The Columbia River delineates much of Oregon's northern boundary with Washington (state), Washington, while the Snake River delineates much of it ...
retains enough toxins in their livers from ingested newts to be effectively poisonous to small local predators (such as crows and fox
Foxes are small to medium-sized, omnivorous mammals belonging to several genera of the family Canidae. They have a flattened skull, upright, triangular ears, a pointed, slightly upturned snout, and a long bushy tail (or ''brush'').
Twelve sp ...
es).
Snake venoms are complex mixtures of protein
Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...
s, 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. The proteins can potentially be a mix of neurotoxin
Neurotoxins are toxins that are destructive to nerve tissue (causing neurotoxicity). Neurotoxins are an extensive class of exogenous chemical neurological insultsSpencer 2000 that can adversely affect function in both developing and mature ner ...
s (which attack the nervous system), hemotoxins (which attack the circulatory system), cytotoxins (which attack the cells directly), bungarotoxin
Bungarotoxins are toxins found in the venom of snakes and kraits. Bites from these animals can result in severe symptoms including bleeding or hemorrhage, paralysis and tissue damage that can result in amputation. The paralytic effects of venom are ...
s (related to neurotoxins, but also directly affect muscle tissue), 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.
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.
It has been suggested that all snakes may be venomous to a certain degree, with harmless snakes having weak venom and no fangs. According to this theory, most snakes that are labelled "nonvenomous" would be considered harmless because they either lack a venom delivery method or are incapable of delivering enough to endanger a human. The theory postulates that snakes may have evolved from a common lizard ancestor that was venomous, and also that venomous lizards like the gila monster, beaded lizard
The Mexican beaded lizard (''Heloderma horridum'') is a species of lizard in the Family (biology), family Helodermatidae, one of the two species of venomous beaded lizards found principally in Mexico and southern Guatemala. It and congener (biolo ...
, monitor lizard
Monitor lizards are lizards in the genus ''Varanus,'' the only extant genus in the family Varanidae. They are native to Africa, Asia, and Oceania, and one species is also found in the Americas as an invasive species. About 80 species are recogn ...
s, and the now-extinct mosasaurs
Mosasaurs (from Latin ''Mosa'' meaning the 'Meuse', and Greek ' meaning 'lizard') comprise a group of extinct, large marine reptiles from the Late Cretaceous. Their first fossil remains were discovered in a limestone quarry at Maastricht on the ...
, may have derived from this same common ancestor. They share this " venom clade" with various other saurian species.
Venomous snakes are classified in two taxonomic families:
* Elapids – cobras including king cobras, kraits
''Bungarus'' is a genus of venomous elapid snakes, the kraits ("krait" is pronounced , rhyming with "kite"), found in South and Southeast Asia. The genus ''Bungarus'' has 16 species.
Distribution
Kraits are found in tropical Asia, from near Ir ...
, mamba
Mambas are fast moving highly venomous snakes of the genus ''Dendroaspis'' (which literally means "tree Asp (reptile), asp") in the family Elapidae. Four Neontology, extant species are recognised currently; three of those four species are essen ...
s, Australian copperheads, sea snake
Sea snakes, or coral reef snakes, are elapid snakes that inhabit marine environments for most or all of their lives. They belong to two subfamilies, Hydrophiinae and Laticaudinae. Hydrophiinae also includes Australasian terrestrial snakes, wher ...
s, and coral snake
Coral snakes are a large group of elapid snakes that can be divided into two distinct groups, the Old World coral snakes and New World coral snakes. There are 16 species of Old World coral snakes, in three genera (''Calliophis'', '' Hemibungarus' ...
s.
* Viperids
The Viperidae (vipers) are a family of snakes found in most parts of the world, except for Antarctica, Australia, Hawaii, Madagascar, and various other isolated islands. They are venomous and have long (relative to non-vipers), hinged fangs t ...
– vipers, rattlesnake
Rattlesnakes are venomous snakes that form the genera ''Crotalus'' and ''Sistrurus'' of the subfamily Crotalinae (the pit vipers). All rattlesnakes are vipers. Rattlesnakes are predators that live in a wide array of habitats, hunting small anim ...
s, copperheads/ cottonmouths, and bushmasters.
There is a third family containing the ''opistoglyphous'' (rear-fanged) snakes (as well as the majority of other snake species):
* Colubrid
Colubridae (, commonly known as colubrids , from la, coluber, 'snake') is a family of snakes. With 249 genera, it is the largest snake family. The earliest species of the family date back to the Oligocene epoch. Colubrid snakes are found on ever ...
s – boomslang
The boomslang (, , or ; ''Dispholidus typus'') is a large, highly venomous snake in the family Colubridae.
Taxonomy and etymology
Its common name means "tree snake" in Afrikaans and Dutch – ''boom'' meaning "tree", and ''slang'' meaning "sna ...
s, tree snakes, vine snakes, cat snakes, although not all colubrids are venomous.
Reproduction
Although a wide range of reproductive modes are used by snakes, all employ internal fertilization. This is accomplished by means of paired, forked hemipenes
A hemipenis (plural hemipenes) is one of a pair of intromittent organs of male squamata, squamates (snakes, lizards and amphisbaenia, worm lizards). Hemipenes are usually held inverted within the body, and are everted for reproduction via erecti ...
, which are stored, inverted, in the male's tail.[Capula (1989), p. 117.] The hemipenes are often grooved, hooked, or spined—designed to grip the walls of the female's cloaca
In animal anatomy, a cloaca ( ), plural cloacae ( or ), is the posterior orifice that serves as the only opening for the digestive, reproductive, and urinary tracts (if present) of many vertebrate animals. All amphibians, reptiles and birds, a ...
. The clitoris
The clitoris ( or ) is a female sex organ present in mammals, ostriches and a limited number of other animals. In humans, the visible portion – the glans – is at the front junction of the labia minora (inner lips), above the ope ...
of the female snake consists of two structures located between the cloaca and the scent glands.
Most species of snakes lay eggs which they abandon shortly after laying. However, a few species (such as the king cobra) construct nests and stay in the vicinity of the hatchlings after incubation. 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
Ovoviviparity, ovovivipary, ovivipary, or aplacental viviparity is a term used as a "bridging" form of reproduction between egg-laying oviparous and live-bearing viviparous reproduction. Ovoviviparous animals possess embryos that develop insi ...
and retain the eggs within their bodies until they are almost ready to hatch.[Capula (1989), p. 118.] Several species of snake, such as the boa constrictor and green anaconda, are fully viviparous
Among animals, viviparity is development of the embryo inside the body of the parent. This is opposed to oviparity which is a reproductive mode in which females lay developing eggs that complete their development and hatch externally from the m ...
, nourishing their young through a placenta
The placenta is a temporary embryonic and later fetal organ that begins developing from the blastocyst shortly after implantation. It plays critical roles in facilitating nutrient, gas and waste exchange between the physically separate mater ...
as well as a yolk sac
The yolk sac is a membranous sac attached to an embryo, formed by cells of the hypoblast layer of the bilaminar embryonic disc. This is alternatively called the umbilical vesicle by the Terminologia Embryologica (TE), though ''yolk sac'' is far ...
; this is highly unusual among reptiles, and normally found in requiem sharks
Requiem sharks are sharks of the family Carcharhinidae in the order Carcharhiniformes. They are migratory, live-bearing sharks of warm seas (sometimes of brackish or fresh water) and include such species as the tiger shark, bull shark, le ...
or placental mammals
Placental mammals (infraclass Placentalia ) are one of the three extant subdivisions of the class Mammalia, the other two being Monotremata and Marsupialia. Placentalia contains the vast majority of extant mammals, which are partly distinguishe ...
. Retention of eggs and live birth are most often associated with colder environments.
Sexual selection
Sexual selection is a mode of natural selection in which members of one biological sex mate choice, choose mates of the other sex to mating, mate with (intersexual selection), and compete with members of the same sex for access to members of t ...
in snakes is demonstrated by the 3,000 species that each use different tactics in acquiring mates. Ritual combat between males for the females they want to mate
Mate may refer to:
Science
* Mate, one of a pair of animals involved in:
** Mate choice, intersexual selection
** Mating
* Multi-antimicrobial extrusion protein, or MATE, an efflux transporter family of proteins
Person or title
* Friendship ...
with includes topping, a behavior exhibited by most viperids in which one male will twist around the vertically elevated fore body of its opponent and force it downward. It is common for neck-biting to occur while the snakes are entwined.
Facultative parthenogenesis
Parthenogenesis
Parthenogenesis (; from the Greek grc, παρθένος, translit=parthénos, lit=virgin, label=none + grc, γένεσις, translit=génesis, lit=creation, label=none) is a natural form of asexual reproduction in which growth and development ...
is a natural form of reproduction in which growth and development of embryos occur without fertilization. ''Agkistrodon contortrix'' (copperhead) and ''Agkistrodon piscivorus'' (cottonmouth) can reproduce by facultative parthenogenesis, meaning that they are capable of switching from a sexual
Sex is the biological distinction of an organism between male and female.
Sex or SEX may also refer to:
Biology and behaviour
* Animal sexual behaviour
**Copulation (zoology)
** Human sexual activity
**Non-penetrative sex, or sexual outercourse
...
mode of reproduction to an asexual mode. The most likely type of parthenogenesis to occur is automixis
''Automixis'' is the fusion of (typically haploid) nuclei or gametes derived from the same individual. The term covers several reproductive mechanisms, some of which are parthenogenetic.
Diploidy might be restored by the doubling of the chromoso ...
with terminal fusion, a process in which two terminal products from the same meiosis
Meiosis (; , since it is a reductional division) is a special type of cell division of germ cells in sexually-reproducing organisms that produces the gametes, such as sperm or egg cells. It involves two rounds of division that ultimately resu ...
fuse to form a diploid zygote
A zygote (, ) is a eukaryotic cell formed by a fertilization event between two gametes. The zygote's genome is a combination of the DNA in each gamete, and contains all of the genetic information of a new individual organism.
In multicellula ...
. This process leads to genome-wide homozygosity, expression of deleterious recessive allele
An allele (, ; ; modern formation from Greek ἄλλος ''állos'', "other") is a variation of the same sequence of nucleotides at the same place on a long DNA molecule, as described in leading textbooks on genetics and evolution.
::"The chro ...
s, and often to developmental abnormalities. Both captive-born and wild-born copperheads and cottonmouths 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
''Epicrates maurus'' is a species of non-venomous constrictor in the family Boidae, commonly found in the Amazon region of South America. The common name for this species is the brown rainbow boa. This species is semi-arboreal, spending time both ...
'') can also reproduce by facultative parthenogenesis, resulting in production of WW female progeny. The WW females are likely produced by terminal automixis.
Embryonic Development
Snake embryonic development initially follows similar steps as any vertebrate embryo
An embryo is an initial stage of development of a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male spe ...
. The snake embryo begins as a zygote
A zygote (, ) is a eukaryotic cell formed by a fertilization event between two gametes. The zygote's genome is a combination of the DNA in each gamete, and contains all of the genetic information of a new individual organism.
In multicellula ...
, undergoes rapid cell division, forms a germinal disc
The blastodisc, also called the germinal disc, is the embryo-forming part on the yolk of the egg of an animal that undergoes discoidal meroblastic cleavage. Discoidal cleavage occurs in those animals with a large proportion of yolk in their eggs, ...
, also called a blastodisc, then undergoes gastrulation
Gastrulation is the stage in the early embryonic development of most animals, during which the blastula (a single-layered hollow sphere of cells), or in mammals the blastocyst is reorganized into a multilayered structure known as the gastrula. Be ...
, neurulation
Neurulation refers to the folding process in vertebrate embryos, which includes the transformation of the neural plate into the neural tube. The embryo at this stage is termed the neurula.
The process begins when the notochord induces the formati ...
, and organogenesis. Cell division and proliferation continues until an early snake embryo develops and the typical body shape of a snake can be observed. Multiple features differentiate the embryologic development of snakes from other vertebrates, two significant factors being the elongation of the body and the lack of limb development.
The elongation in snake body is accompanied by a significant increase in vertebra
The spinal column, a defining synapomorphy shared by nearly all vertebrates,Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristic ...
count (mice have 60 vertebrae, whereas snakes may have over 300). This increase in vertebrae is due to an increase in somites during embryogenesis, leading to an increased number of vertebrae which develop. Somites are formed at the presomitic mesoderm due to a set of oscillatory genes that direct the somitogenesis clock. The snake somitogenesis clock operates at a frequency 4 times that of a mouse (after correction for developmental time), creating more somites, and therefore creating more vertebrae. This difference in clock speed is believed to be caused by differences in ''Lunatic fringe'' gene expression, a gene involved in the somitogenesis clock.
There is ample literature focusing on the limb development/lack of development in snake embryos and the gene expression associated with the different stages. In basal snakes, such as the python, embryos in early development exhibit a hind limb bud
The limb bud is a structure formed early in vertebrate limb development. As a result of interactions between the ectoderm and underlying mesoderm, formation occurs roughly around the fourth week of development. In the development of the human em ...
that develops with some cartilage and a cartilaginous pelvic element, however this degenerates before hatching. This presence of vestigial development suggests that some snakes are still undergoing hind limb reduction before they are eliminated. There is no evidence in basal snakes of forelimb rudiments and no examples of snake forelimb bud initiation in embryo, so little is known regarding the loss of this trait. Recent studies suggests that hind limb reduction could be due to mutations in enhancers for the SSH
The Secure Shell Protocol (SSH) is a cryptographic network protocol for operating network services securely over an unsecured network. Its most notable applications are remote login and command-line execution.
SSH applications are based on a ...
gene, however other studies suggested that mutations within the Hox Genes or their enhancers could contribute to snake limblessness. Since multiple studies have found evidence suggesting different genes played a role in the loss of limbs in snakes, it is likely that multiple gene mutations had an additive effect leading to limb loss in snakes
Behavior
Winter dormancy
In regions where winters are too cold for snakes to tolerate while remaining active, local species will enter a period of brumation
Dormancy is a period in an organism's life cycle when growth, development, and (in animals) physical activity are temporarily stopped. This minimizes metabolic activity and therefore helps an organism to conserve energy. Dormancy tends to be clos ...
. Unlike hibernation
Hibernation is a state of minimal activity and metabolic depression undergone by some animal species. Hibernation is a seasonal heterothermy characterized by low body-temperature, slow breathing and heart-rate, and low metabolic rate. It most ...
, in which the dormant mammals are actually asleep, brumating reptiles are awake but inactive. Individual snakes may brumate in burrows, under rock piles, or inside fallen trees, or large numbers of snakes may clump together in hibernacula.
Feeding and diet
All snakes are strictly carnivorous, preying
Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill the ...
on small animals including lizards, frogs, other snakes, small mammals, birds, eggs, fish, snails, worms, and insects. Snakes cannot bite or tear their food to pieces so must swallow their prey whole. The eating habits of a snake are largely influenced by body size; smaller snakes eat smaller prey. Juvenile pythons might start out feeding on lizards or mice and graduate to small deer or antelope as an adult, for example.
The snake's jaw
The jaw is any opposable articulated structure at the entrance of the mouth, typically used for grasping and manipulating food. The term ''jaws'' is also broadly applied to the whole of the structures constituting the vault of the mouth and serv ...
is a complex structure. Contrary to the popular belief that snakes can dislocate their jaws, they have an extremely flexible lower jaw, the two halves of which are not rigidly attached, and numerous other joints in the skull, which allow the snake to open its mouth wide enough to swallow prey whole, even if it is larger in diameter than the snake itself. For example, the African egg-eating snake has flexible jaws adapted for eating eggs much larger than the diameter of its head. This snake has no teeth, but does have bony protrusions on the inside edge of its spine
Spine or spinal may refer to:
Science Biology
* Vertebral column, also known as the backbone
* Dendritic spine, a small membranous protrusion from a neuron's dendrite
* Thorns, spines, and prickles, needle-like structures in plants
* Spine (zoolog ...
, which it uses to break the shell when eating eggs.
The majority of snakes eat a variety of prey animals, but there is some specialization in certain species. King cobras and the Australian bandy-bandy
The bandy-bandy (''Vermicella annulata''), also commonly known as the hoop snake, is a species of venomous snake in the Family (biology), family Elapidae. The word bandy-bandy (bandi-bandi) traces back to the indigenous dialect of Worimi languag ...
consume other snakes. Species of the family Pareidae
Pareidae is a small family of snakes found largely in southeast Asia, with an isolated subfamily endemic to southwestern India. It encompasses 42 species in four genera divided into two subfamilies: Pareinae and Xylophiinae. Both families are tho ...
have more teeth on the right side of their mouths than on the left, as they mostly prey on snails and the shells usually spiral clockwise.
Some snakes have a venomous bite, which they use to kill their prey before eating it. Other snakes kill their prey by constriction
Constriction is a method used by various snake species to kill or subdue their prey. Although some species of venomous and mildly venomous snakes do use constriction to subdue their prey, most snakes which use constriction lack venom. The snake i ...
, while some swallow their prey when it is still alive.
After eating, snakes become dormant to allow the process of digestion to take place; this is an intense activity, especially after consumption of large prey. In species that feed only sporadically, the entire intestine
The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system that leads from the mouth to the anus. The GI tract contains all the major organs of the digestive system, in humans ...
enters a reduced state between meals to conserve energy. The digestive system is then 'up-regulated' to full capacity within 48 hours of prey consumption. Being ectothermic ("cold-blooded"), the surrounding temperature plays an important role in the digestion process. The ideal temperature for snakes to digest food is . There is a huge amount of metabolic
Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run cell ...
energy involved in a snake's digestion, for example the surface body temperature of the South American rattlesnake ('' Crotalus durissus'') increases by as much as during the digestive process. If a snake is disturbed after having eaten recently, it will often regurgitate its prey to be able to escape the perceived threat. When undisturbed, the digestive process is highly efficient; the snake's digestive enzymes
Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates into different molecule ...
dissolve and absorb everything but the prey's hair (or feathers) and claws, which are excreted along with waste
Waste (or wastes) are unwanted or unusable materials. Waste is any substance discarded after primary use, or is worthless, defective and of no use. A by-product, by contrast is a joint product of relatively minor economic value. A waste prod ...
.
Hooding and spitting
Hooding (expansion of the neck area) is a visual deterrent, mostly seen in cobras (elapids), and is primarily controlled by rib muscles. Hooding can be accompanied by spitting venom towards the threatening object, and producing a specialized sound; hissing. Studies on captive cobras showed that 13 to 22% of the body length is raised during hooding.
Locomotion
The lack of limbs does not impede the movement of snakes. They have developed several different modes of locomotion to deal with particular environments. Unlike the gaits of limbed animals, which form a continuum, each mode of snake locomotion is discrete and distinct from the others; transitions between modes are abrupt.
Lateral undulation
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 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 forward-moving waves).
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 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.
Concertina
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.
Arboreal
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.
Rectilinear
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 python
Python may refer to:
Snakes
* Pythonidae, a family of nonvenomous snakes found in Africa, Asia, and Australia
** ''Python'' (genus), a genus of Pythonidae found in Africa and Asia
* Python (mythology), a mythical serpent
Computing
* Python (pro ...
s, boa
Kwon Bo-ah (; born November 5, 1986), known professionally as BoA, is a South Korean singer, songwriter, dancer, record producer and actress. One of the most successful and influential Korean entertainers, she has been dubbed the " Queen of K- ...
s, and viper
The Viperidae (vipers) are a family of snakes found in most parts of the world, except for Antarctica, Australia, Hawaii, Madagascar, and various other isolated islands. They are venomous and have long (relative to non-vipers), hinged fangs tha ...
s 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
Bite
Snakes do not ordinarily prey on humans. Unless startled or injured, most snakes prefer to avoid contact and will not attack humans. With the exception of large constrictors, nonvenomous snakes are not a threat to humans. The bite of a nonvenomous snake is usually harmless; their teeth are not adapted for tearing or inflicting a deep puncture wound, but rather grabbing and holding. Although the possibility of infection and tissue damage is present in the bite of a nonvenomous snake, venomous snakes present far greater hazard to humans. The World Health Organization
The World Health Organization (WHO) is a specialized agency of the United Nations responsible for international public health. The WHO Constitution states its main objective as "the attainment by all peoples of the highest possible level of h ...
(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
India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the seventh-largest country by area, the second-most populous country, and the most populous democracy in the world. Bounded by the Indian Ocean on the so ...
, 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 viper
The Crotalinae, commonly known as pit vipers,Mehrtens JM (1987). ''Living Snakes of the World in Color''. New York: Sterling Publishers. 480 pp. . crotaline snakes (from grc, κρόταλον ''krotalon'' castanet), or pit adders, are a subfa ...
s, with the exception of the coral snake
Coral snakes are a large group of elapid snakes that can be divided into two distinct groups, the Old World coral snakes and New World coral snakes. There are 16 species of Old World coral snakes, in three genera (''Calliophis'', '' Hemibungarus' ...
. To produce antivenom, a mixture of the venoms of the different species of rattlesnake
Rattlesnakes are venomous snakes that form the genera ''Crotalus'' and ''Sistrurus'' of the subfamily Crotalinae (the pit vipers). All rattlesnakes are vipers. Rattlesnakes are predators that live in a wide array of habitats, hunting small anim ...
s, 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 have an allergic reaction to antivenom. Antivenom for the more dangerous species (such as mamba
Mambas are fast moving highly venomous snakes of the genus ''Dendroaspis'' (which literally means "tree Asp (reptile), asp") in the family Elapidae. Four Neontology, extant species are recognised currently; three of those four species are essen ...
s, taipan
Taipans are snakes of the genus ''Oxyuranus'' in the elapid family. They are large, fast-moving, highly venomous, and endemic to Australia and New Guinea. Three species are recognised, one of which, the coastal taipan, has two subspecies. Taipan ...
s, and cobras) is made in a similar manner in India, South Africa, and Australia, although these antivenoms are species-specific.
Snake charmers
In some parts of the world, especially in India, snake charming is a roadside show performed by a charmer. In such a show, the snake charmer carries a basket containing a snake that he seemingly charms by playing tunes with his flutelike musical instrument, to which the snake responds. The snake is in fact responding to the movement of the flute, not the sound it makes, as snakes lack external ears (though they do have internal ears).
The Wildlife Protection Act of 1972 in India technically prohibits snake charming on the grounds of reducing animal cruelty. Other types of snake charmers use a snake and mongoose show, where the two animals have a mock fight; however, this is not very common, as the animals may be seriously injured or killed. Snake charming as a profession is dying out in India because of competition from modern forms of entertainment and environment laws proscribing the practice. Many Indians have never seen snake charming and it is becoming a folktale of the past.
Trapping
The ''Irulas'' tribe of Andhra Pradesh
Andhra Pradesh (, abbr. AP) is a state in the south-eastern coastal region of India. It is the seventh-largest state by area covering an area of and tenth-most populous state with 49,386,799 inhabitants. It is bordered by Telangana to the ...
and Tamil Nadu
Tamil Nadu (; , TN) is a States and union territories of India, state in southern India. It is the List of states and union territories of India by area, tenth largest Indian state by area and the List of states and union territories of India ...
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. 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
Bill Haast (December 30, 1910 – June 15, 2011) was the owner and operator, from 1947 until 1984, of the Miami Serpentarium, a tourist attraction south of Miami, Florida, where he extracted venom from snakes in front of paying customers. Afte ...
, Austin Stevens
Austin Stevens (born 19 May 1950) is a South African-born Australian naturalist, herpetologist, wildlife photographer, documentarian, television personality, and author. He is best known as the host of the Animal Planet nature documentary seri ...
, Steve Irwin, and Jeff Corwin
Jeffrey Corwin (born July 11, 1967) is an American biologist and wildlife conservation movement, conservationist, known for hosting Disney Channel's ''Going Wild with Jeff Corwin'', ''The Jeff Corwin Experience'' on Animal Planet, American Broa ...
, prefer to catch them using bare hands.
Consumption
Although snakes are not commonly thought of as food, their consumption is acceptable in some cultures and may even be considered a delicacy. Snake soup
Snake soup or stew () is a popular Cantonese cuisine, Cantonese delicacy and health supplement in Hong Kong, which contains the meats of at least two types of snakes as the main ingredients. The soup tastes slightly sweet because of the addition ...
is popular in Cantonese cuisine
Cantonese or Guangdong cuisine, also known as Yue cuisine ( or ) is the cuisine of Guangdong province of China, particularly the provincial capital Guangzhou, and the surrounding regions in the Pearl River Delta including Hong Kong and Maca ...
, consumed by locals in the autumn to warm their bodies. Western cultures document the consumption of snakes only under extreme circumstances of hunger, with the exception of cooked rattlesnake
Rattlesnakes are venomous snakes that form the genera ''Crotalus'' and ''Sistrurus'' of the subfamily Crotalinae (the pit vipers). All rattlesnakes are vipers. Rattlesnakes are predators that live in a wide array of habitats, hunting small anim ...
meat, which is commonly consumed in Texas
Texas (, ; Spanish language, Spanish: ''Texas'', ''Tejas'') is a state in the South Central United States, South Central region of the United States. At 268,596 square miles (695,662 km2), and with more than 29.1 million residents in 2 ...
and parts of the Midwestern United States
The Midwestern United States, also referred to as the Midwest or the American Midwest, is one of four census regions of the United States Census Bureau (also known as "Region 2"). It occupies the northern central part of the United States. I ...
.
In Asia
Asia (, ) is one of the world's most notable geographical regions, which is either considered a continent in its own right or a subcontinent of Eurasia, which shares the continental landmass of Afro-Eurasia with Africa. Asia covers an area ...
n countries such as China, Taiwan, Thailand, Indonesia, Vietnam, and Cambodia, drinking the blood of a snake—particularly the cobra—is believed to increase sexual virility. When possible, the blood is drained while the cobra is still alive, and it is usually mixed with some form of liquor
Liquor (or a spirit) is an alcoholic drink produced by distillation of grains, fruits, vegetables, or sugar, that have already gone through alcoholic fermentation. Other terms for liquor include: spirit drink, distilled beverage or hard ...
to improve the taste.
The use of snakes in alcohol is accepted in some Asian countries. In such cases, one or more snakes are left to steep in a jar or container of liquor, as this is claimed to make the liquor stronger (as well as more expensive). One example of this is the Habu
is a Ryukyuan and Japanese name referring to certain venomous snakes:
* The following species are found in the Ryukyu Islands of Japan:
** ''Protobothrops elegans'', a.k.a. the Sakishima habu, found in the southern Ryukyu Islands
** ''Protobothr ...
snake, which is sometimes placed in the Okinawa
is a prefecture of Japan. Okinawa Prefecture is the southernmost and westernmost prefecture of Japan, has a population of 1,457,162 (as of 2 February 2020) and a geographic area of 2,281 km2 (880 sq mi).
Naha is the capital and largest city ...
n liqueur ''Habushu
is an ''awamori''-based liqueur made in Okinawa, Japan. Other common names include Habu Sake or Okinawan Snake Wine. Habushu is named after the habu snake, ''Trimeresurus flavoviridis'', which belongs to the pit viper family and is closely re ...
'' (ブ酒), also known as "Habu Sake".
Snake wine
Snake wine (; vi, rượu rắn; km, ស្រាពស់, ) 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 ...
(蛇酒) is an alcoholic beverage produced by infusing whole snakes in rice wine
Rice wine is an alcoholic beverage fermented and distilled from rice, traditionally consumed in East Asia, Southeast Asia and South Asia. Rice wine is made by the fermentation of rice starch that has been converted to sugars. Microbes are the so ...
or grain alcohol. First recorded as being consumed in China during the Western Zhou dynasty
The Western Zhou ( zh, c=, p=Xīzhōu; c. 1045 BC – 771 BC) was a royal dynasty of China and the first half of the Zhou dynasty. It began when King Wu of Zhou overthrew the Shang dynasty at the Battle of Muye and ended when the Quanrong nomad ...
, this drink is considered an important curative and is believed to reinvigorate a person according to traditional Chinese medicine
Traditional Chinese medicine (TCM) is an alternative medical practice drawn from traditional medicine in China. It has been described as "fraught with pseudoscience", with the majority of its treatments having no logical mechanism of action ...
.
Pets
In the Western world
The Western world, also known as the West, primarily refers to the various nations and state (polity), states in the regions of Europe, North America, and Oceania. , some snakes are kept as pets, especially docile species such as the ball python and corn snake. To meet the demand, a captive breeding
Captive breeding, also known as captive propagation, is the process of plants or animals in controlled environments, such as wildlife reserves, zoos, botanic gardens, and other conservation facilities. It is sometimes employed to help species that ...
industry has developed. Snakes bred in captivity are considered preferable to specimens caught in the wild and tend to make better pets. Compared with more traditional types of companion animal, snakes can be very low-maintenance pets; they require minimal space, as most common species do not exceed in length, and can be fed relatively infrequently—usually once every five to 14 days. Certain snakes have a lifespan of more than 40 years if given proper care.
Symbolism
In ancient Mesopotamia, Nirah
Nirah was a Mesopotamian god who served as the messenger (''šipru'') of Ištaran, the god of Der. He was depicted in the form of a snake.
Name and character
The name Nirah means "little snake" in Sumerian. It could be written with the log ...
, the messenger god of Ištaran
Ištaran (Ishtaran, sux, ) was a Mesopotamian god who was the tutelary deity of the city of Der, a Sumerian city state positioned east of the Tigris on the border between Sumer and Elam. It is known that he was a judge deity, and his positi ...
, was represented as a serpent on ''kudurru
A kudurru was a type of stone document used as a boundary stone and as a record of land grants to vassals by the Kassites and later dynasties in ancient Babylonia between the 16th and 7th centuries BC. The original kudurru would typically be stor ...
s'', or boundary stones
A boundary marker, border marker, boundary stone, or border stone is a robust physical marker that identifies the start of a land boundary or the change in a boundary, especially a change in direction of a boundary. There are several other ty ...
. Representations of two intertwined serpents are common in Sumerian art and Neo-Sumerian artwork and still appear sporadically on cylinder seals and amulets until as late as the thirteenth century BC. The horned viper ('' Cerastes cerastes'') appears in Kassite
The Kassites () were people of the ancient Near East, who controlled Babylonia after the fall of the Old Babylonian Empire c. 1531 BC and until c. 1155 BC (short chronology).
They gained control of Babylonia after the Hittite sack of Babylon ...
and Neo-Assyrian kudurrus and is invoked in Assyria
Assyria (Neo-Assyrian cuneiform: , romanized: ''māt Aššur''; syc, ܐܬܘܪ, ʾāthor) was a major ancient Mesopotamian civilization which existed as a city-state at times controlling regional territories in the indigenous lands of the A ...
n texts as a magical protective entity. A dragon-like creature with horns, the body and neck of a snake, the forelegs of a lion, and the hind-legs of a bird appears in Mesopotamian art from the Akkadian Period until the Hellenistic Period
In Classical antiquity, the Hellenistic period covers the time in Mediterranean history after Classical Greece, between the death of Alexander the Great in 323 BC and the emergence of the Roman Empire, as signified by the Battle of Actium in 3 ...
(323 BC–31 BC). This creature, known in Akkadian Akkadian or Accadian may refer to:
* Akkadians, inhabitants of the Akkadian Empire
* Akkadian language, an extinct Eastern Semitic language
* Akkadian literature, literature in this language
* Akkadian cuneiform
Cuneiform is a logo- syllabi ...
as the ''mušḫuššu
The ''mušḫuššu'' (; formerly also read as or ) or mushkhushshu ( or ), is a creature from ancient Mesopotamian mythology. A mythological hybrid, it is a scaly animal with hind legs resembling the talons of an eagle, lion-like forelimbs, a ...
'', meaning "furious serpent", was used as a symbol for particular deities and also as a general protective emblem. It seems to have originally been the attendant of the Underworld god Ninazu
Ninazu ( sux, ) was a Mesopotamian god of the underworld of Sumerian origin. He was also associated with snakes and vegetation, and with time acquired the character of a warrior god. He was frequently associated with Ereshkigal, either as a s ...
, but later became the attendant to the Hurrian
The Hurrians (; cuneiform: ; transliteration: ''Ḫu-ur-ri''; also called Hari, Khurrites, Hourri, Churri, Hurri or Hurriter) were a people of the Bronze Age Near East. They spoke a Hurrian language and lived in Anatolia, Syria and Northern ...
storm-god Tishpak, as well as, later, Ninazu's son Ningishzida, the Babylonian national god Marduk
Marduk (Cuneiform: dAMAR.UTU; Sumerian: ''amar utu.k'' "calf of the sun; solar calf"; ) was a god from ancient Mesopotamia and patron deity of the city of Babylon. When Babylon became the political center of the Euphrates valley in the time of ...
, the scribal god Nabu
Nabu ( akk, cuneiform: 𒀭𒀝 Nabû syr, ܢܵܒܼܘܼ\ܢܒܼܘܿ\ܢܵܒܼܘܿ Nāvū or Nvō or Nāvō) is the ancient Mesopotamian patron god of literacy, the rational arts, scribes, and wisdom.
Etymology and meaning
The Akkadian "nab ...
, and the Assyrian national god Ashur.
In Egyptian history
The history of Egypt has been long and wealthy, due to the flow of the Nile River with its fertile banks and delta, as well as the accomplishments of Egypt's native inhabitants and outside influence. Much of Egypt's ancient history was a myste ...
, the snake occupies a primary role with the Nile cobra adorning the crown of the pharaoh in ancient times. It was worshipped
Worship is an act of religious devotion usually directed towards a deity. It may involve one or more of activities such as veneration, adoration, praise, and praying. For many, worship is not about an emotion, it is more about a recognition ...
as one of the gods and was also used for sinister purposes: murder of an adversary and ritual suicide (Cleopatra
Cleopatra VII Philopator ( grc-gre, Κλεοπάτρα Φιλοπάτωρ}, "Cleopatra the father-beloved"; 69 BC10 August 30 BC) was Queen of the Ptolemaic Kingdom of Egypt from 51 to 30 BC, and its last active ruler.She was also a ...
). The ouroboros was a well-known ancient Egyptian symbol of a serpent swallowing its own tail. The precursor to the ouroboros was the "Many-Faced", a serpent with five heads, who, according to the Amduat
The Amduat ( egy, jmj dwꜣt, literally "That Which Is In the Afterworld", also translated as "Text of the Hidden Chamber Which is in the Underworld" and "Book of What is in the Underworld"; ar, كتاب الآخرة, Kitab al-Akhira) is an imp ...
, the oldest surviving Book of the Afterlife, was said to coil around the corpse of the sun god Ra protectively. The earliest surviving depiction of a "true" ouroboros comes from the gilded shrines in the tomb of Tutankhamun
Tutankhamun (, egy, twt-ꜥnḫ-jmn), Egyptological pronunciation Tutankhamen () (), sometimes referred to as King Tut, was an Egyptian pharaoh who was the last of his royal family to rule during the end of the Eighteenth Dynasty (ruled ...
. In the early centuries AD, the ouroboros was adopted as a symbol by Gnostic
Gnosticism (from grc, γνωστικός, gnōstikós, , 'having knowledge') is a collection of religious ideas and systems which coalesced in the late 1st century AD among Jewish and early Christian sects. These various groups emphasized pe ...
Christians and chapter 136 of the ''Pistis Sophia
''Pistis Sophia'' ( grc-koi, Πίστις Σοφία) is a Gnostic text discovered in 1773, possibly written between the 3rd and 4th centuries AD. The existing manuscript, which some scholars place in the late 4th century, relates one Gnostic g ...
'', an early Gnostic text, describes "a great dragon whose tail is in its mouth". In medieval alchemy, the ouroboros became a typical western dragon with wings, legs, and a tail.
In the Bible
The Bible (from Koine Greek , , 'the books') is a collection of religious texts or scriptures that are held to be sacred in Christianity, Judaism, Samaritanism, and many other religions. The Bible is an anthologya compilation of texts of a ...
, King Nahash of Ammon, whose name means "Snake", is depicted very negatively, as a particularly cruel and despicable enemy of the ancient Hebrews.
The ancient Greeks used the Gorgoneion
In Ancient Greece, the Gorgoneion (Greek: Γοργόνειον) was a special apotropaic amulet showing the Gorgon head, used by the Olympian deities Athena and Zeus: both are said to have worn the gorgoneion as a protective pendant,. and often ...
, a depiction of a hideous face with serpents for hair, as an apotropaic symbol to ward off evil. In a Greek myth described by Pseudo-Apollodorus in his '' Bibliotheca'', Medusa was a Gorgon with serpents for hair whose gaze turned all those who looked at her to stone and was slain by the hero Perseus
In Greek mythology, Perseus (Help:IPA/English, /ˈpɜːrsiəs, -sjuːs/; Greek language, Greek: Περσεύς, Romanization of Greek, translit. Perseús) is the legendary founder of Mycenae and of the Perseid dynasty. He was, alongside Cadmus ...
. In the Roman poet Ovid
Pūblius Ovidius Nāsō (; 20 March 43 BC – 17/18 AD), known in English as Ovid ( ), was a Roman poet who lived during the reign of Augustus. He was a contemporary of the older Virgil and Horace, with whom he is often ranked as one of the th ...
's ''Metamorphoses
The ''Metamorphoses'' ( la, Metamorphōsēs, from grc, μεταμορφώσεις: "Transformations") is a Latin narrative poem from 8 CE by the Roman poet Ovid. It is considered his ''magnum opus''. The poem chronicles the history of the wo ...
'', Medusa is said to have once been a beautiful priestess of Athena
Athena or Athene, often given the epithet Pallas, is an ancient Greek goddess associated with wisdom, warfare, and handicraft who was later syncretized with the Roman goddess Minerva. Athena was regarded as the patron and protectress of ...
, whom Athena turned into a serpent-haired monster after she was raped by the god Poseidon
Poseidon (; grc-gre, Ποσειδῶν) was one of the Twelve Olympians in ancient Greek religion and myth, god of the sea, storms, earthquakes and horses.Burkert 1985pp. 136–139 In pre-Olympian Bronze Age Greece, he was venerated as a ch ...
in Athena's temple. In another myth referenced by the Boeotia
Boeotia ( ), sometimes Latinized as Boiotia or Beotia ( el, Βοιωτία; modern: ; ancient: ), formerly known as Cadmeis, is one of the regional units of Greece. It is part of the region of Central Greece. Its capital is Livadeia, and its lar ...
n poet Hesiod
Hesiod (; grc-gre, Ἡσίοδος ''Hēsíodos'') was an ancient Greek poet generally thought to have been active between 750 and 650 BC, around the same time as Homer. He is generally regarded by western authors as 'the first written poet i ...
and described in detail by Pseudo-Apollodorus, the hero Heracles
Heracles ( ; grc-gre, Ἡρακλῆς, , glory/fame of Hera), born Alcaeus (, ''Alkaios'') or Alcides (, ''Alkeidēs''), was a divine hero in Greek mythology, the son of Zeus and Alcmene, and the foster son of Amphitryon.By his adoptive ...
is said to have slain the Lernaean Hydra, a multiple-headed serpent which dwelt in the swamps of Lerna.
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
In Greek mythology, Cadmus (; grc-gre, Κάδμος, Kádmos) was the legendary Phoenician founder of Boeotian Thebes. He was the first Greek hero and, alongside Perseus and Bellerophon, the greatest hero and slayer of monsters before the da ...
all perished – leading to the term "Cadmean victory
A Cadmean victory ( el, καδμεία νίκη, translit=kadmeía níkē) is a reference to a victory involving one's own ruin,Liddell, Henry George (Compiler), Scott, Robert (Compiler), Jones, Henry Stuart (Editor), McKenzie, Roderick. ''A Greek- ...
" (i.e. a victory involving one's own ruin).
Three medical symbols involving snakes that are still used today are Bowl of Hygieia
The Bowl of Hygieia is one of the symbols of pharmacology, and along with the Rod of Asclepius it is one of the most ancient and important symbols related to medicine in western countries. Hygieia was the Greek goddess of health, hygiene, cleanl ...
, symbolizing pharmacy, and the Caduceus
The caduceus (☤; ; la, cādūceus, from grc-gre, κηρύκειον "herald's wand, or staff") is the staff carried by Hermes in Greek mythology and consequently by Hermes Trismegistus in Greco-Egyptian mythology. The same staff was also ...
and Rod of Asclepius
In Greek mythology, the Rod of Asclepius (⚕; grc, Ράβδος του Ασκληπιού, , sometimes also spelled Asklepios), also known as the Staff of Aesculapius and as the asklepian, is a serpent-entwined rod wielded by the Greek god A ...
, which are symbols denoting medicine in general.[
One of the etymologies proposed for the common female first name '' Linda'' is that it might derive from Old German ''Lindi'' or ''Linda'', meaning a serpent.
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 ]Shiva
Shiva (; sa, शिव, lit=The Auspicious One, Śiva ), also known as Mahadeva (; ɐɦaːd̪eːʋɐ, or Hara, is one of the principal deities of Hinduism. He is the Supreme Being in Shaivism, one of the major traditions within Hindu ...
and Vishnu
Vishnu ( ; , ), also known as Narayana and Hari, is one of the principal deities of Hinduism. He is the supreme being within Vaishnavism, one of the major traditions within contemporary Hinduism.
Vishnu is known as "The Preserver" within t ...
is 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
Naga Panchami is a day of traditional worship of Nag (or Naja or Naga) or snakes (which are associated with the mythical Nāga beings) observed by Hindus, Jains, and Buddhists throughout India, Nepal, and other countries where Hindu, Jain, and ...
each year on which day snakes are venerated and prayed to. See also ''Nāga
The Nagas (IAST: ''nāga''; Devanāgarī: नाग) are a divine, or semi-divine, race of half-human, half-serpent beings that reside in the netherworld (Patala), and can occasionally take human or part-human form, or are so depicted in art. ...
''.
In India there is another mythology about snakes. Commonly known in Hindi
Hindi (Devanāgarī: or , ), or more precisely Modern Standard Hindi (Devanagari: ), is an Indo-Aryan language spoken chiefly in the Hindi Belt region encompassing parts of northern, central, eastern, and western India. Hindi has been de ...
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 snake
Snakes are elongated, Limbless vertebrate, limbless, carnivore, carnivorous reptiles of the suborder Serpentes . Like all other Squamata, squamates, snakes are ectothermic, amniote vertebrates covered in overlapping Scale (zoology), scales. Ma ...
is one of the 12 celestial animals of Chinese zodiac, in the Chinese calendar
The traditional Chinese calendar (also known as the Agricultural Calendar 曆; 农历; ''Nónglì''; 'farming calendar' Former Calendar 曆; 旧历; ''Jiùlì'' Traditional Calendar 曆; 老历; ''Lǎolì'', is a lunisolar calendar ...
.
Many ancient Peruvian cultures worshipped nature. They emphasized animals and often depicted snakes in their art.
Religion
Snakes are used in Hinduism
Hinduism () is an Indian religion or '' dharma'', a religious and universal order or way of life by which followers abide. As a religion, it is the world's third-largest, with over 1.2–1.35 billion followers, or 15–16% of the global p ...
as a part of ritual worship. In the annual Nag Panchami
Naga Panchami is a day of traditional worship of Nag (or Naja or Naga) or snakes (which are associated with the mythical Nāga beings) observed by Hindus, Jains, and Buddhists throughout India, Nepal, and other countries where Hindu, Jain, and ...
festival, participants worship either live cobras or images of Nāga
The Nagas (IAST: ''nāga''; Devanāgarī: नाग) are a divine, or semi-divine, race of half-human, half-serpent beings that reside in the netherworld (Patala), and can occasionally take human or part-human form, or are so depicted in art. ...
s. Lord Shiva
Shiva (; sa, शिव, lit=The Auspicious One, Śiva ), also known as Mahadeva (; ɐɦaːd̪eːʋɐ, or Hara, is one of the principal deities of Hinduism. He is the Supreme Being in Shaivism, one of the major traditions within Hindu ...
is depicted in most images with a snake coiled around his neck. Puranic
Purana (; sa, , '; literally meaning "ancient, old"Merriam-Webster's Encyclopedia of Literature (1995 Edition), Article on Puranas, , page 915) is a vast genre of Indian literature about a wide range of topics, particularly about legends an ...
literature includes various stories associated with snakes, for example Shesha
Shesha (Sanskrit: शेष; ) , also known as Sheshanaga (Sanskrit: शेषनाग; ) or Adishesha (), is a serpentine demigod (Naga) and Nagaraja (King of all serpents), as well as a primordial being of creation in Hinduism. In the Puran ...
is said to hold all the planets of the Universe on his hoods and to constantly sing the glories of Vishnu
Vishnu ( ; , ), also known as Narayana and Hari, is one of the principal deities of Hinduism. He is the supreme being within Vaishnavism, one of the major traditions within contemporary Hinduism.
Vishnu is known as "The Preserver" within t ...
from all his mouths. Other notable snakes in Hinduism are Vasuki, Takshaka, Karkotaka, and Pingala. The term ''Nāga'' is used to refer to entities that take the form of large snakes in Hinduism and Buddhism
Buddhism ( , ), also known as Buddha Dharma and Dharmavinaya (), is an Indian religion or philosophical tradition based on teachings attributed to the Buddha. It originated in northern India as a -movement in the 5th century BCE, and gra ...
.
Snakes have been widely revered in many cultures, such as in ancient Greece
Ancient Greece ( el, Ἑλλάς, Hellás) was a northeastern Mediterranean civilization, existing from the Greek Dark Ages of the 12th–9th centuries BC to the end of classical antiquity ( AD 600), that comprised a loose collection of cult ...
where the serpent was seen as a healer. Asclepius
Asclepius (; grc-gre, Ἀσκληπιός ''Asklēpiós'' ; la, Aesculapius) is a hero and god of medicine in ancient Religion in ancient Greece, Greek religion and Greek mythology, mythology. He is the son of Apollo and Coronis (lover of ...
carried a serpent wound around his wand, a symbol seen today on many ambulances. In Judaism
Judaism ( he, ''Yahăḏūṯ'') is an Abrahamic, monotheistic, and ethnic religion comprising the collective religious, cultural, and legal tradition and civilization of the Jewish people. It has its roots as an organized religion in the ...
, the snake of brass
Brass is an alloy of copper (Cu) and zinc (Zn), in proportions which can be varied to achieve different mechanical, electrical, and chemical properties. It is a substitutional alloy: atoms of the two constituents may replace each other with ...
is also a symbol of healing, of one's life being saved from imminent death.
In religious terms, the snake and jaguar
The jaguar (''Panthera onca'') is a large cat species and the only living member of the genus '' Panthera'' native to the Americas. With a body length of up to and a weight of up to , it is the largest cat species in the Americas and the th ...
were arguably the most important animals in ancient Mesoamerica
Mesoamerica is a historical region and cultural area in southern North America and most of Central America. It extends from approximately central Mexico through Belize, Guatemala, El Salvador, Honduras, Nicaragua, and northern Costa Rica. W ...
. "In states of ecstasy, lords dance a serpent dance; great descending snakes adorn and support buildings from Chichen Itza
Chichen Itza , es, Chichén Itzá , often with the emphasis reversed in English to ; from yua, Chiʼchʼèen Ìitshaʼ () "at the mouth of the well of the Itza people" was a large pre-Columbian city built by the Maya people of the Terminal ...
to Tenochtitlan, and the Nahuatl
Nahuatl (; ), Aztec, or Mexicano is a language or, by some definitions, a group of languages of the Uto-Aztecan language family. Varieties of Nahuatl are spoken by about Nahua peoples, most of whom live mainly in Central Mexico and have smaller ...
word ''coatl'' meaning serpent or twin, forms part of primary deities such as Mixcoatl, Quetzalcoatl
Quetzalcoatl (, ; Spanish: ''Quetzalcóatl'' ; nci-IPA, Quetzalcōātl, ket͡saɬˈkoːaːt͡ɬ (Modern Nahuatl pronunciation), in honorific form: ''Quetzalcōātzin'') is a deity in Aztec culture and literature whose name comes from the Nahu ...
, and Coatlicue." In the Maya and Aztec calendars, the fifth day of the week was known as Snake Day.
In some parts of Christianity
Christianity is an Abrahamic monotheistic religion based on the life and teachings of Jesus of Nazareth. It is the world's largest and most widespread religion with roughly 2.38 billion followers representing one-third of the global pop ...
, the redemptive work of Jesus Christ
Jesus, likely from he, יֵשׁוּעַ, translit=Yēšūaʿ, label=Hebrew/Aramaic ( AD 30 or 33), also referred to as Jesus Christ or Jesus of Nazareth (among other names and titles), was a first-century Jewish preacher and religious ...
is compared to saving one's life through beholding the Nehushtan (serpent of brass). Snake handlers use snakes as an integral part of church worship, to demonstrate their faith in divine protection. However, more commonly in Christianity, the serpent has been depicted as a representative of evil and sly plotting, as seen in the description in Genesis
Genesis may refer to:
Bible
* Book of Genesis, the first book of the biblical scriptures of both Judaism and Christianity, describing the creation of the Earth and of mankind
* Genesis creation narrative, the first several chapters of the Book of ...
of a snake tempting Eve
Eve (; ; ar, حَوَّاء, Ḥawwāʾ; el, Εὕα, Heúa; la, Eva, Heva; Syriac: romanized: ) is a figure in the Book of Genesis in the Hebrew Bible. According to the origin story, "Creation myths are symbolic stories describing how the ...
in the Garden of Eden
In Abrahamic religions, the Garden of Eden ( he, גַּן־עֵדֶן, ) or Garden of God (, and גַן־אֱלֹהִים ''gan-Elohim''), also called the Terrestrial Paradise, is the Bible, biblical paradise described in Book of Genesis, Genes ...
.[ ]Saint Patrick
Saint Patrick ( la, Patricius; ga, Pádraig ; cy, Padrig) was a fifth-century Romano-British Christian missionary and bishop in Ireland. Known as the "Apostle of Ireland", he is the primary patron saint of Ireland, the other patron saints be ...
is purported to have expelled all snakes from Ireland while converting the country to Christianity in the 5th century, thus explaining the absence of snakes there.
In Christianity and Judaism, the snake makes its infamous appearance in the first book of the Bible when a serpent appears before Adam and Eve and tempts them with the forbidden fruit from the Tree of Knowledge. The snake returns in the Book of Exodus
The Book of Exodus (from grc, Ἔξοδος, translit=Éxodos; he, שְׁמוֹת ''Šəmōṯ'', "Names") is the second book of the Bible. It narrates the story of the Exodus, in which the Israelites leave slavery in Biblical Egypt through t ...
when Moses
Moses hbo, מֹשֶׁה, Mōše; also known as Moshe or Moshe Rabbeinu (Mishnaic Hebrew: מֹשֶׁה רַבֵּינוּ, ); syr, ܡܘܫܐ, Mūše; ar, موسى, Mūsā; grc, Mωϋσῆς, Mōÿsēs () is considered the most important pro ...
turns his staff into a snake as a sign of God's power, and later when he makes the Nehushtan, a bronze snake on a pole that when looked at cured the people of bites from the snakes that plagued them in the desert. The serpent makes its final appearance symbolizing Satan
Satan,, ; grc, ὁ σατανᾶς or , ; ar, شيطانالخَنَّاس , also known as Devil in Christianity, the Devil, and sometimes also called Lucifer in Christianity, is an non-physical entity, entity in the Abrahamic religions ...
in the Book of Revelation
The Book of Revelation is the final book of the New Testament (and consequently the final book of the Christian Bible). Its title is derived from the first word of the Koine Greek text: , meaning "unveiling" or "revelation". The Book of R ...
: "And he laid hold on the dragon the old serpent, which is the devil and Satan, and bound him for a thousand years."
In Neo-Paganism and Wicca
Wicca () is a modern Pagan religion. Scholars of religion categorise it as both a new religious movement and as part of the occultist stream of Western esotericism. It was developed in England during the first half of the 20th century and was ...
, the snake is seen as a symbol of wisdom and knowledge. Additionally, snakes are sometimes associated with Hecate
Hecate or Hekate, , ; grc-dor, Ἑκάτᾱ, Hekátā, ; la, Hecatē or . is a goddess in ancient Greek religion and mythology, most often shown holding a pair of torches, a key, snakes, or accompanied by dogs, and in later periods depicte ...
, the Greek goddess of witchcraft
Witchcraft traditionally means the use of magic or supernatural powers to harm others. A practitioner is a witch. In medieval and early modern Europe, where the term originated, accused witches were usually women who were believed to have us ...
.
Medicine
Several compounds from snake venoms are being researched as potential treatments or preventatives for pain, cancers, arthritis, stroke, heart disease, hemophilia, and hypertension, and to control bleeding (e.g. during surgery).
See also
* Limbless vertebrates
Many vertebrates have evolved limbless, limb-reduced, or apodous forms. Reptiles have on a number of occasions evolved into limbless forms – snakes, amphisbaenia, and legless lizards (limb loss in lizards has evolved independently several ti ...
* List of Serpentes families
This is an overview of the suborder Serpentes, its two infraorders (subdivisions) and the families they contain. This is the group of reptiles commonly known as snakes.
Taxonomy
There are two infraorders of living snakes: Alethinophidia and S ...
* List of snakes
List of snakes refers to a variety of different articles and different criteria. these are listed below.
Lists General lists
*General lists:
** Snake#Taxonomy
** List of reptile genera#Order Squamata
**List of snakes by common name
** List of sn ...
* Ophiology
Herpetology (from Greek language, Greek ἑρπετόν ''herpetón'', meaning "reptile" or "creeping animal") is the branch of zoology concerned with the study of amphibians (including frogs, toads, salamanders, newts, and caecilians (gymnop ...
* Snakebot
The SnakeBot, also known as a snake robot, is a biomorphic hyper-redundant robot that resembles a biological snake. Snake robots come in many shapes and sizes, from as long as four stories (earthquake SnakeBot developed by SINTEF) to a medical S ...
* Snake detection theory
The snake detection theory, also sometimes called the snake detection hypothesis, suggests that snakes have contributed to the evolution of primates' visual system.
According to the theory, predatory pressure from snakes has selected individuals ...
* Snake skeleton
A snake skeleton consists primarily of the skull, vertebrae, and ribs, with only vestigial remnants of the limbs.
Skull
The skull of a snake is a very complex structure, with numerous joints to allow the snake to swallow prey far larger than i ...
* Spinal osteoarthropathy (reptile disease)
* ''The New Encyclopedia of Snakes
''The New Encyclopedia of Snakes'' is an encyclopedia by Chris Mattison.
Book summary
The encyclopedia has information about snakes that is listed from A-Z. The book has pictures and information about snake morphology (biology), morphology, habita ...
''
* The Snakes of Europe and Snakes of Europe Wikibooks:Snakes of Europe, a wikibook
* Venomous snake
Venomous snakes are Species (biology), species of the Suborder (biology), suborder Snake, Serpentes that are capable of producing Snake venom, venom, which they use for killing prey, for defense, and to assist with digestion of their prey. The v ...
*
*
References
Further reading
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
External links
*
*
*
*
*
BBC Nature:
Snake news, and video clips from BBC programmes past and present.
at Life is Short but Snakes are Long
{{Authority control
Cenomanian first appearances
Taxa named by Carl Linnaeus
Extant Cenomanian first appearances