Fossil range: Cretaceous - Recent
|[[taxon|Superfamilies and Families]]
Snakes are "long-bodied, limb-reduced reptiles descended from lizards" that live in most of the tropical and temperate regions of the world. The formal biological classification of snakes is within a group of animals called squamates (see classification Order: Squamata) that also includes such animals as lizards, Amphisbaenians and Caecilians. Serpent is a common synonym for snake, and the scientific order of snakes is called Serpentes.
Several species of legless lizard resemble snakes, but are not more closely related to them then lizards with normal legs.
All snakes are obligate carnivores, eating small animals including lizards, other snakes, rodents and other mammals ,as well as birds, eggs and insects. Some species of snakes take a mixed diet, and others primarily eat a very specialized one, such as earthworms. Although all snakes swallow their prey whole, not all snakes do so while the animal is either conscious or alive. Some snakes have a venomous bite which they use to disable their prey before engulfing it with their open mouths. Other snakes kill their prey by constriction before swallowing their meal.
The prey that snakes take is usually large as compared to the size of their closed mouths. How can snakes manage to swallow such outsized items without chewing? They 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 "unhook" their jaws to open their mouths wide enough to encompass a diameter larger than the snake itself. Of course, although the snake's body can stretch to accommodate prey that might be larger than the undistended snake's body, there are limits to how much the snake can stretch—and snakes instinctively know these limits. They will not attempt to take prey that are too large. "Because larger individuals tend to select larger prey than smaller individuals, differences in size tend to reduce competition between juveniles and adults of the same species."(reference for quote: Kenneth R Porter: Food Relations of Amphibians and Reptilesin Herpetology WB Saunders Company 1972 ISBN 0-7216-7295-7 page 327)
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. In species which feed only sporadically, the entire intestine enters a reduced state between meals to conserve energy, and the digestive system is 'up-regulated' to full capacity within 48 hours of prey consumption. So much metabolic energy is involved in digestion that in Crotalus durissus, the Mexican rattlesnake, an increase of body temperature to as much as 14 degrees Celsius above the surrounding environment has been observed. Because of this, a snake disturbed will often regurgitate its prey in order to be able to escape. 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 have been known to occasionally die from trying to swallow an animal that is too big. Snake digestive acids are unable to digest most plant matter, which passes through the digestive system mostly untouched.
Snakes do not normally prey on people. While some aggressive species exist, most will not attack humans unless startled or injured, preferring instead to avoid contact. Most snakes are either non-venomous or possess venom that is not lethal to humans.
The skin is covered in scales. Snakes use specialized belly scales, called scutes, to grip surfaces as they are propelled by their accordion-like motion. The body scales may be smooth, keeled, or granular. Their eyelids are transparent "spectacle" scales which remain permanently closed, called brille. They shed their skin periodically. Unlike other reptiles, this is done in one piece, like pulling off a sock, with the snake rubbing its nose against something rough, like a rock, for instance, creating a rip in the skin around the nose and the mouth until the skin is completely removed. The primary purpose of shedding this is to grow; shedding also removes 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. If there is not enough humidity in the air while snakes are shedding their skin, it can be very dangerous for the snake, because the dry skin does not shed. Skin that remains attached to the snake can harbour diseases and parasites. A tail tip that is not removed can constrict as the snake grows, cutting off the blood supply to the end of the tail causing it to drop off. A retained spectacle can cause the snake to become blind in the affected eye.
While snake vision is unremarkable (generally being best in arboreal species and worst in burrowing species), it can detect movement. Some snakes, like the Asian vine snake, have binocular vision. In most snakes, the lens moves back and forth within the eyeball to focus. In addition, 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.
Snakes have no external ears, but have a bone called the quadrate under the skin on either side of the head which focuses sound into the cochlea. Their sense of hearing is most sensitive to frequencies around 200–300 Hz.
A snake smells by using its forked tongue to collect airborne particles then passing them to the Jacobson's organ or the Vomeronasal organ in the mouth for examination. The fork in the tongue gives the snake a sort of directional sense of smell. The part of the body which is in direct contact with the surface of the ground is very sensitive to vibration, thus a snake is able to sense other animals approaching.
The left lung is very small or even absent, as snakes' tubular bodies and requirement for distensibility for the accommodation of prey combine to yield modification of most of their organs to be both long and thin. Additionally, apparently as a "space saving" adaptation, sometimes one of paired organs is vestigial. For example, snakes have only one functioning lung. This lung contains a vascularized anterior portion and a posterior portion which does not function in gas exchange. This 'saccular lung' may be used to adjust buoyancy in some aquatic snakes and its function remains unknown in terrestrial species. 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 used by the males for stimulation of females during mating. The penis of male snakes is not single, as in most vertebrates, but double: a pair of hemipenes.
Snakes utilize a variety of methods of movement which allows 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. 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, an undulatory motion used to move across slippery mud or loose sand.
Documented deaths from snake bites are uncommon in most areas of the world. Only about 450 species of snakes are venomous (only about 250 that can kill a human), and among the 7,000 Americans bitten by venomous snakes every year, fewer than fifteen die; (lightning kills more). See snakebites for more information, including prevention of snake bites and first aid treatment.
A venomous snake is a snake that uses modified saliva, venom, delivered through fangs in its mouth, to immobilize or kill its prey. (In contrast, most non-venomous species are constrictors which suffocate their prey.) Snake venom can be either a neurotoxin or a hemotoxin. Neurotoxins attack the nervous system, while hemotoxins attack the circulatory system. Venomous snakes include several families of snakes and do not constitute a formal classification group used in taxonomy.
In some parts of the world, especially in India and Pakistan, snake charming is a roadside show. The snake charmer carries a basket that contains a snake which he seemingly charms by playing tunes from his flute-like musical instrument, to which the snake responds. However, snakes' hearing is not very sensitive to the range of the charmer's instrument, so they may not be able to hear the music at all. Many snake charmers are good sleight-of-hand artists. The snake moves corresponding to the flute movement and the vibrations from the tapping of the charmer's foot which is not noticed by the public. They rarely catch their snakes and the snakes are either nonvenomous or defanged cobras. Sometimes these people exploit the fear of snakes by releasing snakes into the neighbourhood and then offering to rid the residence of snakes. Other snake charmers also have a snake and mongoose show, where both the animals have a mock fight; however, this is not very common, as the snakes, as well as the mongooses, may be seriously injured or killed. Snake charming is now discouraged in India as a contribution to forest & snake conservation, and in some places in India it is banned by law.
Despite the existence of snake charmers, there have also been professional snake catchers or wranglers. The tribals of "Irulas" from Andhra Pradesh and Tamil Nadu in India have been practicing this art for generations. They generally don't use gimmicks and with the help of a simple stick catch the snakes from the fields or houses. They are also known to eat some of the snakes they catch and are very useful in rat extermination in the villages. Their knowledge of snakes and their behaviour is uncanny. Modern day snake trapping involves a herpetologist using a long stick with a "V" shaped end. Some like the late Steve Irwin prefer to catch them using bare hands.
At least one tribe of natives uses a specialized form of snake catching as a rite of passage to manhood. The young man of interest will wrap his leg heavily in some type of cloth all the way to the inseam. He will then stick his leg in a burrow containing a large python, typically a reticulated python. After the snake swallows most of his leg several other members of the tribe will pull him out of the hole along with the snake. The snake is then killed and the man's leg removed from the snake. These snakes can be over 20 ft long and it is possible for the man to have his leg dislocated. The scent of a prey animal may be used to help convince the snake to swallow the leg.
Human consumption of snakes
In some cultures, the consumption of snakes is acceptable or even considered a delicacy, prized for its alleged pharmaceutical effect of warming the heart. Western cultures document the consumption of snake under extreme circumstances of hunger. However, human consumption of snake meat, especially when eaten raw, may lead to dangerous parasitic infections in humans. Rattlesnake meat is eaten in the western USA. In Asian countries drinking the blood of snakes, particularly the cobra, is believed to increase sexual virility. The blood is drained while the cobra is still alive when possible, and is usually mixed with some form of liquor.
In Egyptian history, the snake occupies a primary role with the Nile cobra adorning the crown of the pharaoh in ancient times. It was worshipped as one of the Gods and was also used for sinister purposes: murder of an adversary and ritual suicide (Cleopatra).
In Greek Mythology snakes are often associated with deadly and dangerous antagonists. The 9 headed Hydra Hercules defeated and the three Gorgon sisters are literary examples. Medusa was one of the three Gorgon sisters who Perseus defeated. Medusa is described as a hideous mortal, with snakes instead of hair and the power to turn men to stone with her gaze.
India is often called the land of 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 and Vishnu is depicted often as sleeping only on a 7 headed snake. 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 Nagpanchami each year on which day snakes are venerated and prayed to.
In the first book (Genesis) of the Bible, a snake appears before Adam and Eve and tempts them with the forbidden fruit. It is also seen in Exodus when Moses, as a sign of God's power, turns his stick into a snake; snakes are similarly produced by the pharaoh's magic-practicing priests, but Moses' snake devours them. Later Moses made 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. Jesus instructed his disciples to be as shrewd as snakes and as innocent as doves.
The Ouroboros is a symbol that is associated with many different religions and customs, and is also claimed to be related to Alchemy. The Ouroboros or Oroboros is a snake manifesting its own tail in a clock-wise direction (from the head to the tail) in the shape of a circle, representing manifestation of one's own life and rebirth, leading to immortality. The Ouroboros is also associated with the popular manga, Fullmetal Alchemist or Hagane no Renkinjutsushi by Hiromu Arakawa.
In the Chinese zodiac, people born in the year of the snake (1917, 1929, 1941, 1953, 1965, 1977, 1989, 2001) are meant to be deep. They say little and possess great wisdom. They never have to worry about money; they are financially fortunate. Snake people are often quite vain, selfish, and a bit stingy. Yet they have tremendous sympathy for others and try to help those less fortunate. Snake people tend to overdo, since they have doubts about other people's judgment and prefer to rely on themselves. They are determined in whatever they do and hate to fail. Although calm on the surface, they are intense and passionate. Snake people are usually good-looking and sometimes have marital problems because they are fickle. They are most compatible with the Ox and Rooster.
Snakes as pets
Snakes have been listed as one of the top ten creepy pets by About.com Many people have been known to have snakes as pets, and even deaths have been reported to occur due to improper handling of snakes, especially snake species that constrict such as Boa Constrictors.
- Crotalus horridus
- Green Anaconda
- Turkish viper
- Vipera Avicennae
- Vipera echis
- Vipera lebetina xanthina
- Vipera ocellata
- Snake venom
- The word comes from Old English snaca, and ultimately from the Proto-Indo-European base snag- or sneg-, "to crawl"), also known as ophidians. A love of snakes is called ophiophilia, a fear of snakes is called ophidiophobia. A specialist in snakes is an ophiologist.
- reference for quote:Michael SY Lee, University of Queensland, Brisbane, Australia: Serpentes (Snakes). Standard article in: Encyclopedia of Life Sciences Copyright © 2006 by John Wiley & Sons, Inc. All Rights Reserved.
- Tattersall GJ et al.(2004) The thermogenesis of digestion in rattlesnakes, J Exp Biol 207:579-85