Snake, river, United States

Snake, river, 1,038 mi (1,670 km) long, NW United States, the chief tributary of the Columbia; once called the Lewis River. The Snake rises in NW Wyoming, in Yellowstone National Park, flows through Jackson Lake in Grand Teton National Park, then S and W into Idaho and northwest to its junction with the Henrys Fork River. The combined stream runs southwest, then northwest, crossing southern Idaho through the Snake River plain; there are several notable falls. The Snake makes a bend into Oregon and turns north to form the Idaho-Oregon and Idaho-Washington lines (receiving several tributaries, including the Boise and Salmon rivers), then turns at Lewiston, Idaho (at the mouth of the Clearwater River), and flows generally west to join the Columbia River near Pasco, Wash. Hell's Canyon is the greatest of the Snake's many gorges and one of the deepest in the world. Extending c.125 mi (200 km) N along the Oregon-Idaho line, it reaches a maximum depth of c.7,900 ft (2,410 m).

The Snake was explored by the Lewis and Clark expedition (1803–6) and was of major importance in U.S. expansion into the Pacific Northwest. The river is a major source of electricity, having numerous hydroelectric power plants. The upper and middle courses of the Snake and its tributaries are much used for irrigation by private projects (one of the most notable being at Twin Falls) and by projects of the U.S. Bureau of Reclamation, including the Minidoka project, the Boise project, the Palisades project, and the Owyhee project. Four navigation and hydroelectric power projects along the lower Snake provide slack water navigation from the mouth of the Snake 140 mi (225 km) upstream to Lewiston, Idaho. The projects are linked with the navigation system on the Columbia River. The late 1990s brought efforts to restore portions of the river by removing gravel and establishing new islands.

snake, in zoology

snake, common name for an elongated, limbless reptile of the order Squamata, which also includes the lizards. 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.

Characteristics

Anatomy

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. 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 a marine environment and are descended from marine lizards. Support for the latter view comes from recent discovery of the most primitive snake now known, a fossil specimen with two short but well-developed hind legs found in marine sediments in Israel. It lived in a shallow sea 95 million years ago.

Predation

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 venom or zootoxin, any of a variety of poisonous substances produced by animals. In poisonous snakes, venom is secreted in two poison glands, one on each side of the upper jaw, and enters the fang by a duct.
..... Click the link for more information. , 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 snakebite, wound inflicted by the teeth of a snake. The bite of a nonvenomous snake is rarely serious. Venomous snakes have fangs, hollow teeth through which poison is injected into a victim.
..... Click the link for more information. ). 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.

Reproduction

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 garter snake, harmless snake of the genus Thamnophis, abundant from Canada to Central America. There are many common species; members of most species are about 2 ft (60 cm) long.
..... Click the link for more information. (including the ribbon snake), the water snakes, the green, or grass, snakes, the black snakes black snake, name for several snakes, not all closely related, that are black in color. In the United States the name is applied chiefly to the black racer and to the black rat snake (Elaphe obsoleta), both partly arboreal in their habits.
..... Click the link for more information. , the racers racer, name for several related swift, slender snakes, especially those of the genus Coluber. All of the racers are nonpoisonous, nonconstricting, day-active snakes. The black racer, C.
..... Click the link for more information. , the king snakes king snake, name for a number of species of the genus Lampropeltis, nonvenomous, egg-laying, constricting snakes of North America which show much variation in color and markings.
..... Click the link for more information. (including the milk snake), and the bull, hognose, and rat snakes. The family Boidae (boas boa (bō`ə), name for live-bearing constrictor snakes of the family Boidae, found mostly in the Americas.
..... Click the link for more information. and pythons python (pī`thŏn), name for nonvenomous constrictor snakes of the boa family, found in the tropical regions of Africa, Asia,
..... Click the link for more information. ) 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 pit viper, poisonous snake of the family Crotalidae, primarily a New World family. Like the Old World true vipers (family Viperidae), pit vipers have long, hollow, erectile fangs that are folded back against the roof of the mouth except when the snake is striking.
..... Click the link for more information. family; these include the copperhead copperhead, poisonous snake, Ancistrodon contortrix, of the E United States. Like its close relative, the water moccasin, the copperhead is a member of the pit viper family and detects its warm-blooded prey by means of a heat-sensitive organ behind the nostril.
..... Click the link for more information. , water moccasin water moccasin or cottonmouth, highly venomous snake , Ancistrodon piscivorus, of the swamps and bayous of the S United States. Like the closely related copperhead, it is a pit viper and has a heat-sensitive organ for detecting
..... Click the link for more information. , rattlesnake rattlesnake, poisonous New World snake of the pit viper family, distinguished by a rattle at the end of the tail. The head is triangular, being widened at the base. The rattle is a series of dried, hollow segments of skin, which, when shaken, make a whirring sound.
..... Click the link for more information. , fer-de-lance, and bushmaster bushmaster, large venomous snake, Lachesis muta, of Central America and N South America. It is a member of the pit viper family, which also includes the rattlesnake. The largest New World snake, it reaches a length of 8 to 12 ft (2.5–5.5 m).
..... Click the link for more information. . Venomous Old World snakes are the true vipers viper, any of a large number of heavy-bodied, poisonous snakes of the family Viperidae, characterized by erectile, hypodermic fangs. The fangs are folded back against the roof of the mouth except when the snake strikes.
..... Click the link for more information. , including the adder and the asp asp, popular name for several species of viper , one of which, the European asp (Vipera aspis), is native to S Europe. It is also a name for the Egyptian cobra (Naja haja).
..... Click the link for more information. , and members of the cobra family, including the mamba mamba, name for African snakes of the genus Dendroaspis, in the cobra family. Widely distributed throughout Africa except in the deserts, mambas have extremely toxic venom.
..... Click the link for more information. of Africa and the krait of Asia. The poisonous coral snakes coral snake, name for poisonous New World snakes of the same family as the Old World cobras . About 30 species inhabit Mexico, Central America, and N South America; two are found in the United States.
..... Click the link for more information. of the New World also belong to this family. The venomous sea snakes inhabit tropical oceans.

Importance

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 sea snake, name for any of the venomous marine snakes of the family Hydrophidae, found in tropical waters of the Indian and Pacific oceans. The sea snake's body is flattened laterally and its oarlike tail is used as a scull.
..... Click the link for more information. 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 snake worship. The snake has been variously adored as a regenerative power, as a god of evil, as a god of good, as Christ (by the Gnostics), as a phallic deity, as a solar deity, and as a god of death.
..... Click the link for more information. .

Classification

Snakes are classified in the phylum Chordata Chordata (kôrdā`tə,–dä`–)
..... Click the link for more information. , subphylum Vertebrata, class Reptilia, order Squamata, suborder Serpentes.

Bibliography

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).

snake

Internal and external features of a snake.

Any member of about 19 reptile families (suborder Serpentes, order Squamata) that has no limbs, voice, external ears, or eyelids, only one functional lung, and a long, slender body. About 2,900 snake species are known to exist, most living in the tropics. Their skin is covered with scales. They have good eyesight, and they continually taste the surrounding air with their tongues. Though they lack any voice, they are capable of hissing. Most live on the ground, but some are arboreal or aquatic, and some are burrowers. They move by muscular contraction, aided by elongated scales on their abdomen. They focus 70% of their mostly solitary existence on tracking, capturing, and digesting their living prey. The construction of their jaws and bodies enables them to swallow large prey whole. Because they are ectotherms (cold-blooded), a single meal can often sustain them for weeks. Mating and laying eggs or bearing live young are brief seasonal activities. About one-tenth of snake species are venomous; some can kill humans with their bite. Others kill their prey by constriction or simply ingesting. Species range from less than 5 in. (12 cm) to over 30 ft (9 m) long. Snakes grow continuously throughout their lives, shedding their outgrown skin at each growth increment. They are found worldwide, but few species are found on islands or in regions with long winters.