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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.

Contents

1 Feeding

7 Surviving venomous snake bites

8 Lethal venomous snakes

9 Human consumption of snakes

10 Classification

11 Related topics

12 External links

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 people, 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.

Lethal venomous snakes

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] or even considered a delicacy[2], prized for its alleged pharmaceutical effect of warming the heart. It is reported to taste like chicken[3]. Western cultures document the consumption of snake under extreme circumstances of hunger[4]. 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)
  - 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
  - Family 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
  - Family Acrochordidae: file snakes
- Superfamily Xenophidia (Colubroidea = Caenophidia)
  - Family Atractaspididae: mole vipers
  - Family Colubridae: colubrids (over half of all snake species, such as garter snake, rat snake, milk snake, king snake)
  - Family Elapidae: cobras, kraits, coral snakes, Australian copperheads
  - Family Hydrophiidae: sea snakes
  - Family Viperidae: vipers and pit vipers (e.g. rattlesnake, American copperhead)

External links

The Snake is also the name of a river in the western United States of America (See Snake River.)

Categories: Squamata | Scaled reptiles | Snakes | Pets

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10-26-2009 08:16:03
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