snake (in zoology)
snake, common name for an elongated, limbless reptile of the order Squamata, which also includes the xlizards. Most snakes live on the ground, but some are burrowers, arboreal, or aquatic; one group is exclusively marine. In temperate climates they hibernate. They are generally solitary in their habits, although they may congregate in places offering food or shelter, and large numbers may hibernate together. Snakes range in length from about 4 in. (10 cm) to over 30 ft (9 m). Most are protectively colored.
Snakes constitute the suborder Serpentes (or Ophidia). In most snakes limbs are entirely lacking, but a few have traces of hind limbs. The skin, which is covered with horny scales, is shed, usually several times a year. The extremely long, narrow body is associated with distinctive internal features. The number of vertebrae is much larger than in most vertebrates, paired internal organs are arranged linearly rather than side by side, and only one lung is developed, except in members of the boa family, which have two lungs. The jaws of snakes are loosely jointed and extremely flexible. The pointed, backward-curved teeth are fused to the supporting bones of the head. There are no ears or movable eyelids; the eyes are covered by transparent "spectacles," or ocular scales. Snakes have good vision. They do not hear airborne sound waves, but can perceive low-frequency vibrations (100–700 Hz) transmitted from the ground to the bones of the skull. A chemosensory organ opens into the roof of the mouth; it receives stimuli from the forked tongue that constantly tastes the surroundings as the animal moves along. Snakes have no larynx or vocal chords, but are capable of producing a hissing sound.
Locomotion and Limblessness
A snake moves by means of muscular contraction, which can produce several types of locomotion, the commonest types being undulation and straight-line movement. Straight-line movement is aided by the ventral plates, elongated scales on the abdomen that overlap with their open ends pointing toward the tail. These plates can be moved forward by means of muscles attached to the ribs.
It is believed that snakes are descended from lizards, but how and why they evolved toward limblessness is uncertain. Some paleontologists have held that limblessness was an evolutionary advantage in the dense vegetation that formed the early environment of snakes, or that it developed to facilitate burrowing habits, but others believe that the earliest snakes evolved in an aquatic environment and are descended from marine reptiles related to mosasaurs. The fossil evidence for a land or marine origin is inconclusive; the earliest known snakelike reptiles date to some 167 million years ago.
Small snakes feed on insects and larger ones on proportionately larger animals. Their teeth are designed for catching and holding prey, but not for chewing. The construction of the jaws, the ribs, and the expandable skin enable them to swallow very large prey whole. Some snakes capture animals by pinning them to the ground; some—the constrictors—crush them by wrapping their bodies around them and squeezing; still others—the venomous snakes—inject poison into their victims. The poison, or venom, is produced by modified salivary glands from which it passes through either a groove or a hollow bore in the fangs, the enlarged, specialized teeth found in venomous snakes. A snake may bite a person when threatened or alarmed; if the snake is venomous the bite can sometimes prove fatal (see snakebite). Only by familiarity with the appearance of particular species, or by examination of the fangs, can the venomous snakes be distinguished from the harmless ones.
Fertilization is internal in snakes; as in lizards, the males have paired copulatory organs, either of which may be used in mating. Females of some species can store sperm for several years to insure future fertilization. In most species the female lays eggs; in some the eggs are incubated and hatched within the mother's body; in a few there is true viviparity, or live birth, with the young nourished by means of a placenta rather than an egg. Some egg-laying snakes brood the eggs, but there is no parental care of the young.
Types of Snakes
The approximately 2,700 snake species, of which about four fifths are nonvenomous, are distributed throughout the temperate and tropical zones of the world (except in New Zealand, Ireland, and some isolated oceanic islands) and are found in greatest profusion in the tropics. About two thirds of all snake species belong to the family Colubridae; most of these are nonvenomous. Among the harmless colubrid snakes of North America are the garter snakes (including the ribbon snake), the water snakes, the green, or grass, snakes, the black snakes, the racers, the king snakes (including the milk snake), and the bull, hognose, and rat snakes. The family Boidae (boas and pythons) includes the world's largest snakes, the South American anaconda and the Asian reticulated python, as well as the smaller boa constrictor and the tree and sand boas.
Most poisonous New World snakes belong to the pit viper family; these include the copperhead, water moccasin, rattlesnake, fer-de-lance, and bushmaster. Venomous Old World snakes are the true vipers, including the adder and the asp, and members of the cobra family, including the mamba of Africa and the krait of Asia. The poisonous coral snakes of the New World also belong to this family. The venomous sea snakes inhabit tropical oceans.
Snakes are of major importance as pest controllers because of their extensive predation on destructive mammals such as rats and mice. Some, like the sea snakes and pythons, are highly regarded as food in Asia but, although most are probably edible, snakes are not widely used for meat. The skin is often used for belts, bags, and shoes. Venom is removed from snakes for use in treating certain diseases and to make antivenin for snakebites.
See also snake worship.
Snakes are classified in the phylum Chordata, subphylum Vertebrata, class Reptilia, order Squamata, suborder Serpentes.
See A. H. and A. A. Wright, A Handbook of Snakes of the United States and Canada (2 vol., 1957); K. L. Williams and V. Wallach, Snakes of the World (2 vol., 1990).
Snakes are limbless reptiles with long, cylindrical bodies, scaly skin, lidless eyes, and a forked tongue. Most species are not poisonous, some are mildly poisonous, and others produce a deadly poison. The term venom is commonly used to describe the poison produced by a snake.
All snakes are carnivores (meat-eaters) and cold blooded, meaning their body temperature is determined by the environment rather than being internally regulated. For this reason, snakes are found mainly in tropical and temperate regions, and are absent in cold climate zones.
Types of snakes
The 2,700 species of snakes fall into four superfamilies: Boidae (boas, anacondas, and pythons), Elapidae (cobras, coral snakes, mambas, and kraits), Colubridae (king snakes, water snakes, garter snakes, black snakes, and adders, to name only a few) and Viperidae (true vipers and pit vipers).
Members of the Boidae family are among the most primitive of all snakes. They are constrictors that kill their prey by squeezing it to death. Some of the largest snakes are members of this family. Some anacondas, for example, have been known to grow to more than 11 meters (37 feet) in length.
Snakes in the Elapidae family have grooved or hollow fangs in the front of the mouth. The bases of the fangs are connected to the venom gland. Venom is injected when the victim is bitten. Members of this family range in size from the tiny elapids, which may be no more than a few centimeters long, to the feared taipan, which may grow to nearly four meters (12 feet) in length.
The Colubridae family is huge, with more than 1,400 species, and includes the majority of living species. Most colubrids are harmless, but a few are extremely dangerous. Examples are the rear-fanged snakes, such as the African boomslang or the crown snake. These snakes do not release their poison through hollow fangs. Instead, they inject poison by chewing their prey after it is in their mouth.
Members of the Viperidae family are among the most dangerous of all snakes. They include in addition to the vipers themselves the rattlesnake, fer-de-lance, and bushmaster. Most members of the family have a wedge-shaped head that people have come to associate with poisonous snakes.
Anatomy and physiology
Snakes have extremely poor sight and hearing. They detect their prey primarily by means of vibrations, heat, and chemical signals they detect with their other senses. For example, a snake's flicking, forked tongue acts as a chemical collector, drawing chemical "smells" into the mouth. Those smells are then analyzed by two chemical sensors known as Jacobson's organs on the roof of its mouth. This mechanism also allows male snakes to detect females in the reproductive state.
Words to Know
Carnivore: A flesh-eating animal.
Jacobson's organs: Chemical sensors located on the roof of the mouth of a snake used to detect chemical "smells."
Molt: To shed an outer layer of skin at regular intervals.
Venom: A poison produced by a snake.
Another mechanism used by snakes to detect prey is a set of tiny pits or hollows that certain kinds of vipers have on the side or top of their heads. These pits can detect the body heat of prey at considerable distances.
Contrary to popular belief, snakes are not slimy. The scales that cover their bodies are dry but glistening, giving a sheen that offers an appearance of wetness. Scales protect the snake's body from friction and dehydration. They also aid its movement by gripping the surface while powerful muscles propel the body forward, usually with a horizontal waving motion. This method of movement means that snakes cannot move backward.
Instead of eyelids, the eyes of snakes are covered and protected by clear scales. Several times a year, snakes molt, shedding their skin in one complete piece by rubbing against a rough surface.
Snakes' teeth do not allow them to chew and break up the bodies of their prey. Instead, they usually swallow their prey whole. Special ligaments in the snake's hinged jaw permit its mouth to open to as much as a 150-degree angle. Thus, the snake can swallow animals many times larger than the size of its own head. The largest recorded feast was a 130-pound (59-kilogram) antelope swallowed by an African rock python.
Snakes' teeth face inward and prevent the prey from escaping. The snake's strong jaw and throat muscles work the food down the esophagus and into the stomach, where digestion begins. Digestion time differs, and is influenced by temperature. In one instance, a captive python at a room temperature of 30°C (87°F) digested a rabbit in four days. At cooler temperatures (18°C; 64°F), however, digestion took more than two weeks.
The interval between meals also varies. Some snakes go weeks or even months without food. In temperate climates, snakes may fast and hibernate during the winter months. Pregnant females may hibernate and fast seven months, while both sexes fast before shedding.
Hunting and defense
The coloring of a snake's skin scales provides an excellent camouflage from predators and prey. Tree snakes can have a color as green as any leaf in the forest; ground snakes are as brown or dusty grey as the earth and rocks; and sea snakes are dark above and light beneath. Some snakes are brightly colored with vivid patterns that warn potential predators to stay away. An example is the highly venomous coral snake, which has orange, black, and white rings.
Snakes attack only when hungry or threatened. When frightened, they tend to flee. If there is no time for flight, or if snakes are cornered or antagonized, they strike. Venomous snakes have two fangs in the upper jaw that penetrate the flesh of their prey. Poison glands then pump venom through grooves inside the fangs into the prey. Some species of snake inject their prey with toxin and wait until the animal is no longer capable of struggling before eating it. Snake venom is purely a feeding aid, serving both to subdue the prey and to aid in its digestion before it is swallowed.
Nonvenomous constrictors, such as boas, pythons, and anacondas, first snatch their prey in their jaws. Then, with lightning speed, they coil their bodies around the animal, squeezing its thorax to prevent breathing. Amazingly, the prey's bones remain unbroken during this process.
Snakes and humans
Snakes have fascinated and frightened humans for thousands of years. Some cultures still worship snakes, seeing them as creators and protectors. Other cultures fear snakes as devils and symbols of death.
In many ways, snakes serve a valuable function for human societies. They prey on animals, such as rats and mice, that we often regard as pests. Many people enjoy keeping snakes as pets also.
On the other hand, many people have a terrible fear of these reptiles. They may believe that the only good snake is a dead snake. Unfortunately, this attitude leads to the death of many harmless snakes. Yet, as much as most humans fear snakes, snakes fear humans more. Certainly, some snakes can kill a human in a matter of minutes, and no snake should be handled unless positively identified as harmless. However, the estimated risk of venomous snakebites to humans in the United States is 20 times less than being struck by lightning. Overall, a well-educated, healthy respect for snakes would benefit both humans and snakes.
[See also Reptiles ]
SNAKE (Heb. נָחָשׁ, naḥash), a generic name for various species of snake, poisonous and harmless. Both in the Bible and generally in rabbinical literature it is mentioned with ignominy as harmful. It already appears at the dawn of history in the Bible as the enemy of man, enticing Eve. Its punishment was that it would have to crawl upon its belly and lick the earth, and enmity would prevail between it and man: "they shall bruise thy head, and thou shalt bruise their heel" (Gen. 3: 13–15). Slander and speaking evil is compared to the venom of the snake (cf. Ps. 140:4), and it has even been suggested that the Hebrew term for this, lashon ha-ra, is an abbreviation of leshon ha-naḥash ha-ra ("the tongue of the evil snake"). Simeon b. Yohiai stated: "Even with the best of snakes, crush its head" (tj, Kid. 4:11, 66c). It is permitted to slay "the snake of Israel," apparently the viper common in inhabited localities, even on the Sabbath (Shab. 121b). On the other hand, it was recognized that in the ordinary way even the poisonous snake does not attack man unless it is afraid of being attacked. Hence the directive that the recital of the Amidah may not be interrupted "even if a snake is coiled around one's heel" (Ber. 5:1). According to the Jerusalem Talmud, however (Ber. 9a), one may defend oneself against it even when praying, if it appears about to bite. Despite the hatred in general toward snakes, their value in destroying mice was recognized. Some even raised "house snakes" for this purpose (Gen. R. 19:10; this is the "house snake" referred to in tj, Ter. 8:7, 46a).
Only a few of the species of snakes in Israel are poisonous. Eighteen species of nonpoisonous snakes are to be found, seven whose poison kills small creatures only, and seven which are dangerous to man. In addition to the comprehensive term naḥash there is mentioned the saraf which appears to be the general name for poisonous snakes whose poison, so to speak, soref ("burns") the body. Four individual snakes are mentioned in the Bible: צֶפַע or צִפְעוֹני (ẓefa or ẓifoni), אֶפְﬠֶה (efeh), שְׁפִיפוֹן (shefifon), and פֶּטֶן (peten), all of which are poisonous. The ẓefa-ẓifoni is identified with the Palestine viper, Vipera palaestinae, recognizable by the two dark brown wavy stripes extending along the length of the light brown skin. This is the only poisonous snake dwelling in the inhabited regions of Israel. The Bible notes that the ẓifoni "excretes" its poison while the snake "bites" (Prov. 23:32), i.e., the latter bites with all its teeth while the poisonous snake only pricks with the anterior teeth, thus excreting the poison, The genus Viper is also found in northern countries, while other poisonous snakes dwell in hot regions. The Israeli viper is unique in that it lays eggs, while the other species are viviparous. Isaiah (59:5) already notes that the ẓifoni lays eggs and whoever eats them is liable to die from the bite of the serpents breaking out of them. A closely related species, black in color, Atractaspis eingadensis, is found in En-Gedi and its vicinity.
Efeh is mentioned in the Bible as a dangerous desert snake (Isa. 30:6). According to the Midrash, this is the ekhes (Mekh. Va-Yassa, 1), apparently a snake of the genus Echis being meant, two species of which are found in the desert areas of Israel. It can be recognized by the white bands breadthways upon its light brown body. It makes a noise by the rubbing of its scales that sounds like a cry and this may be the origin of its name (פעה; "to cry"). Its poison is very dangerous though it very rarely does harm as it is not found near inhabited places. Shefifon is identified by the Septuagint with Cerastes, a genus of poisonous snakes of which the species Pseudocerastes fieldi, recognizable by glands like protrusions above its eyes, is found in the Negev. It digs into the sand, only its "horns" protruding. The birds, taking them to be worms, peck at them, whereupon the snake strikes, killing them. This apparently is referred to in the verse: "Dan shall be … a shefifon in the path, that biteth the horse's heels" (Gen. 49:17). Its name appears to be connected with the rustling made by its scales. Peten has been identified with the Egyptian cobra, Naja haje. It is not found in Israel though there are indications that solitary specimens may exist in the southern Negev and in Sinai. It is the most dangerous snake of the region. Even outward contact with it can be dangerous (cf. Job 20:14–16). The peten was used by charmers, as is the Indian cobra today, and it is noted that it does not always obey charmers (Ps. 58:5–7). The words (Ps. 58:7), "Break their teeth, O God, in their mouth," may be a reference to the fact that the charmers used to extract the poisonous teeth of the peten. The black peten, Walterinnesia aegyptia, is found in the Judean desert. It is a dangerous poisonous snake in appearance similar to the nonpoisonous black snake. Rabbinical literature mentions poisonous snakes called havarvar, arvad, and akhnai, whose identity has not been established.
Lewysohn, Zool, 234ff.; F.S. Bodenheimer, Animal and Man in Bible Lands (1960), 200; A. Barash and J.H. Hoofien, Zoḥalim (19612); J. Feliks, The Animal World of the Bible (1962), 102ff. add. bibliography: Feliks, Ha-Ẓome'aḥ, 250, 262.
Snakes are the emblems of St Patrick, who was said to have banished them from Ireland.
snake charmer an entertainer who appears to make snakes move by playing music, although the snake is in fact following the movement of the player's instrument rather than the sound of the music. The image is of longstanding, as in the biblical reference in Psalm 58:4–5.
snake in the grass a treacherous or deceitful person. The expression comes originally from Virgil's Eclogues.
snake-oil a term for a substance with no real medicinal value sold as a remedy for all diseases.
snakepit a pit containing poisonous snakes; in early legends, used as a means of execution, as in the story of Gunnar, who is said to have been put to death in this way by Atli.
In the 20th century, the term has been used for a scene of vicious behaviour or ruthless competition, and specifically (after the title of a novel (1947) by M. J. Ward), a mental hospital.
snakes and ladders a children's game in which players move counters along a board, gaining an advantage by moving up pictures of ladders or a disadvantage by moving down pictures of snakes; the game was put on the market in the early part of the 20th century.
snakes in Iceland an allusive phrase referring to something posited only to be dismissed as non-existent; the reference is to Dr Johnson's comment on Horrebow's Natural History of Iceland (1758), to the effect that ‘he could repeat a complete chapter…the whole of which was exactly thus:—“.Chap. lxxii. Concerning Snakes. There are no snakes to be met with throughout the whole island”.’
snake / snāk/ • n. 1. a long limbless reptile (suborder Ophidia or Serpentes) that has no eyelids, and jaws that are capable of considerable extension. Some snakes have a venomous bite. ∎ (in general use) a limbless lizard or amphibian. 2. (also snake in the grass) a treacherous or deceitful person. 3. (in full plumber's snake) a long flexible wire for clearing obstacles in pipes. • v. [ intr.] move or extend with the twisting motion of a snake: a rope snaked down. DERIVATIVES: snake·like / -ˌlīk/ adj.
See also 16. ANIMALS ; 353. REPTILES .
- 1. an abnormal fear of snakes. Also ophiophobia .
- 2. herpetophobia.
- a description of snakes. —ophiographic, adj.
- the worship of snakes. — ophiolater, n.
- the branch of herpetology that studies snakes. Also called snakeology, snakology. —ophiologist, n. —ophiologic, ophiological, adj.
- a form of divination involving snakes.
- snakeology, snakology
a term applied to things or a formation resembling a snake—Wilkes.
Examples : a black snake of men winding across the plain, 1891; snakes of ribbon, 1894.