|
Snakes are cold blooded legless reptiles closely related to lizards, which share
the order Squamata.
There are also several species of legless lizard which superficially resemble snakes, but are not otherwise related to them. A love of snakes
is called ophiophilia.
An old synonym for snake is serpent; in modern usage this usually refers to a mythic or symbolic snake, and
information about such creatures will be found under serpent. This article deals with
the biology of snakes.
All snakes are carnivorous, eating small animals (including lizards and other
snakes), birds, eggs or insects. Some snakes have a venomous bite which they use to kill
their prey before eating it. Other snakes kill their prey by constriction resulting in strangulation. Snakes do not chew their food. Snakes have a very flexible lower jaws, the two halves of which are not rigidly attached, And numerous other joints in their skull (see
snake skull), allowing them to open their mouths wide enough to swallow their
prey whole, even if it is larger in diameter than the snake itself. Contrary to the popular myth, at no point do they "unhinge"
their jaws (disarticulate their mandibular joints). After eating, snakes become torpid while the process of digestion takes place.
The skin is covered in scales. Most snakes use specialized belly scales to move,
gripping surfaces. Their eyelids are transparent "spectacle" scales which remain permanently closed. They shed their skin
periodically. Unlike other reptiles, this is done in one piece, like pulling off a sock. It is thought that the primary purpose
of this is to remove external parasites. This periodic renewal has led to the snake being a symbol of healing and medicine, as
pictured in the Rod of Asclepius.
While detailed vision is thought to be limited, it does not prevent detection of
movement. In addition to their eyes, some snakes (pit vipers, boas, pythons, etc.) have infrared sensitive receptors in deep grooves between the nostril and eye which allow them to 'see' the radiated
heat. As snakes have no external ears, hearing is restricted to
the sensing of vibrations, but this sense is extremely well developed. A snake smells by using its forked tongue to collect airborne particles then passing them to the Jacobson's organ in the mouth for examination. The fork in the
tongue gives the snake a sort of directional sense of smell. The left lung is very small or
sometimes even absent, as snakes' tubular bodies require all of their organs to be long and thin, and to accommodate them all
only one lung is functional.
Snakes utilize a variety of methods of movement which allow them substantial mobility in spite of their legless condition. All
snakes are capable of lateral undulation, in which the body is
flexed side-to-side, and the flexed areas propogate posteriorly, giving the overall shape of a posteriorly propagating sine wave.
In addition, all snakes are capable of concertina movement. In this method of movement can be used to both climb trees and move through small
tunnels. In the case of trees, the branch is grasped by the posterior portion of the body, while the anterior portion is
extended. The anterior portion then grasps the branch, and the posterior portion is pulled forward. This cycle may occur in
several sections of the snake simultaneously. In the case of tunnels, instead of grapsing, the body loops are pressed against the
tunnel walls to attain traction, but the motion is otherwise similar. Another common method of locomotion is rectilinear
locomotion, in which the snake remains straight and propells itself via a ceterpillar-like motion of it's belly-muscles. This
mode is usually only used by very large, heavy snakes, such as large pythons and vipers. The most complex and interesting mode is
sidewinding, a undulatory motion
used to move across slippery mud or loose sand.
A wide range of reproductive modes are used by snakes. All snakes have internal fertilization, accomplished by means of
paired, forked hemipenes, which are
usually stored inverted in the male's tail. Most snakes lay eggs, which most species abandon shortly after laying, however, some
species retain the eggs within their bodies until they are almost ready to hatch. Recently, it has been confirmed that several
species of snake are actually fully livebearing, nourishing their young through a placenta as well as a yolk sac. Retention of
eggs and live birth are commonly, but not exclusively, associated with cold environments, as the retention of the young within
the female allows her to control their temperature more effectively than if the developing young were in external eggs.
Snakes do not prey on humans. While some particularly aggressive species exist, most will not attack a human being unless
startled or injured - preferring instead to avoid contact. In fact, most snakes are non-venomous or have venom that is not
harmful to humans.
Not all snakes dwell on land; sea snakes live in shallow tropical seas.
Some well known snake species are:
Surviving venomous snake bites
There is little reason to fear death from snake bites. Only a quarter of snakes are venomous, and among the 7,000 Americans
bitten by venomous snakes every year, fewer than fifteen die (lightning kills
more). However, if you are bitten by a snake, there are certain procedures to follow. Firstly, move away from the attacking
snake. Secondly, check for one or two puncture wounds on your body. If the site of the bite begins to swell and hurt terribly,
then you are envenomed. If possible, keep the wound below your heart and slowly begin to move toward medical attention.
The venom alone is usually not enough to kill you, but overexerting yourself while envenomed can. Do not tie off the bitten part
to prevent the venom from spreading, as lack of blood circulation may kill
the part. Besides, the venom spreads throughout your system
almost instantaneously upon entry. Despite popular belief, you cannot suck snake venom out through your mouth.
Classification
Order:Squamata
- Suborder Serpentes
- Superfamily Typhlopoidea (Scolecophidia)
- Family Anomalepidae: dawn
blind snakes
- Family Typhlopidae: blind Snakes
- Family Leptotyphlopidae /Glauconiidae: slender blind snakes
- Superfamily Henophidia (Boidea)
- Family Aniliidae /Ilysiidae:
pipe snakes
- Family Anomochilidae dwarf pipe snakes
- Family Boidae: boas and Pythonidae: pythons
- Family Bolyeridae: Round Island
boas
- Family Cylindrophiidae:
Asian pipe snakes
- Family Loxocemidae: Mexican
burrowing pythons
- Family Tropidophiidae
- Family Ungaliophiidae:
dwarf boas
- Family Uropeltidae: shield-tail Snakes
- Family Xenopeltidae: Sunbeam Snakes
- Superfamily Xenophidia (Colubroidea = Caenophidia)
Related topics
External links
The Snake is also the name of a river in the western United States of America (See Snake River.)
|