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.
Feeding
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 death by strangulation. Snakes do not chew their food.
Snakes have a very flexible lower jaw, the two halves of which are not rigidly
attached, and numerous other joints in their skull (see snake skull),
allowing them to open their mouths wide enough to swallow their prey whole, even if it is larger in diameter than the snake
itself. 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.
Digestion is an intensive activity, especially after the consumption of very large prey, and so much metabolic energy is involved
that Crotalus durissus, the Mexican rattlesnake, may actually raise its body temperature as much as 6 degrees above the
surrounding environment. Because of this, a snake disturbed after having eaten recently will often regurgitate the prey in order
to be able to escape the perceived threat. However, when undisturbed, the digestive process is highly efficient, dissolving and
absorbing everything but hair and claws, which are excreted along with uric acid waste.
Snakes do not normally prey on humans, but there are instances of small children being eaten by large constrictors in the
jungle. While some particularly aggressive species exist, most will not attack humans 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.
Skin
The skin is covered in scales. Most snakes use specialized belly scales to move, gripping surfaces. The body scales may be smooth,
keeled, or granular. 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. In "advanced" (Caenophidian) snakes, the broad belly scales and rows of dorsal scales correspond
to the vertebrae, allowing scientists to count the vertebrae without dissection
Perception
While snake vision is unremarkable (generally being best in arboreal species and
worst in burrowing species), it is able to detect movement. In addition to their eyes, some snakes (pit vipers, pythons, and some
boas) 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.
Internal organs
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. Also, many organs that are
paired, such as kidneys or reproductive organs, are staggered within the body, with one located ahead of the other. The most
primitive snakes, including boas and pythons, have anal spurs, a pair of claws
on either side of the cloaca which are the vestiges of limbs. The leg bones and remains
of the pelvis are embedded within the body in these species.
Locomotion
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 propagate posteriorly, giving the overall shape of a posteriorly propagating sine wave.
In addition, all snakes are capable of concertina movement.
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 grasping, 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 propels itself via a
caterpillar-like motion of its 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.
Not all snakes dwell on land; sea snakes live in shallow tropical seas.
Reproduction
A wide range of reproductive modes are used by snakes. All snakes employ internal fertilization, accomplished by means of
paired, forked hemipenes, which are stored inverted in the male's tail. Most
snakes lay eggs, and of those most species abandon them shortly after laying;
however, some species are ovoviviparous and retain the eggs within their
bodies until they are almost ready to hatch. Recently, it has been confirmed that several species of snake are 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.
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 have been envenomated. 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 envenomated can. Do not tie off the
affected area to prevent the venom from spreading, as lack of blood circulation may cause tissue death. Moreover, the venom spreads throughout the circulatory system almost instantaneously upon entry. Despite popular
belief, you cannot suck out snake venom with your mouth.
While only a quarter of snakes are venomous, there are various species that are lethal to humans. The following groups of
lethal snakes can be aggressive and their venom can kill a healthy adult if left untreated for several hours. This list is
incomplete.
Human consumption of snakes
In some cultures, the consumption of snakes is acceptable[1] (http://www.economist.com/displayStory.cfm?story_id=1487714) or even considered a
delicacy[2] (http://www.asiatour.com/x-librar/dining/chinese.htm), prized for its alleged pharmaceutical
effect of warming the heart. It is reported to taste like chicken[3] (http://www.asiatour.com/x-librar/dining/chinese.htm). Western cultures document the
consumption of snake under extreme circumstances of hunger[4] (http://www.gutenberg.org/dirs/1/2/5/9/12595/12595-h/12595-h.htm). However, human consumption
of these snakes, especially the uncooked ones, may often cause deadly infection from rare parasites.
Classification
Order:Squamata
- Suborder Serpentes
- Superfamily Typhlopoidea (Scolecophidia)
- Superfamily Henophidia (Boidea)
- 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.)
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