Boa - biology.

Boa - biology. Boa, common name for nonpoisonous snakes of the boa family. Like all members of this group, boas are constrictors--that is, they kill their prey by squeezing it to death and then they swallow it whole. Boas use the coils of their body to suffocate their prey, rather than crushing it, as is commonly believed. They can stretch their jaws wide apart to swallow animals larger than their heads. Depending on the size of its prey, a boa may take several weeks or longer to digest its food. Many of the exceptionally large snakes of the world are of this family, but not all boas are large. Some are no more than 50 cm (20 in) long when fully grown. Boas vary greatly in color and pattern. The boa family is characterized by vestigial hipbones and hind legs, which can be seen externally as a pair of movable spurs. Boas and pythons are often confused, but they differ in several ways, primarily in the skeleton. Most boas give birth to live young, while pythons lay eggs. Boas are found worldwide, except in Australia, while pythons are found in Africa, Asia, Australia, and the Pacific islands. Probably the best-known boa is the boa constrictor, found in the jungles of Central and South America. Boa constrictors are usually yellowish or grayish, with a pattern of dark brown dorsal saddles; the tail is often reddish-orange. Most adults do not exceed 2 to 3 m (6.6 to 10 ft) in length, although unusually large individuals may reach 4 m (13 ft). Stories of larger boas may have caused boa constrictors to be confused with anacondas (water boas) or with the pythons of Asia. Tree boas, such as the brightly colored emerald tree boa, live in trees and have strong, prehensile tails. With their triangular heads, elliptical eye pupils, and long, curved front teeth, they resemble the venomous vipers. Some smaller boas, such as the rubber boa, range throughout much of the northwestern United States. Found as far north as British Columbia, Washington, and Montana, the rubber boa, whose shiny brown skin resembles rubber, is a burrowing animal. Because of its blunt head and tail, it is sometimes called a two-headed snake. See Anaconda; Python. Scientific classification: Boas belong to the family Boidae. The boa constrictor is classified as Boa constrictor, the emerald tree boa as Corallus canina, and the rubber boa as Charina bottae. Contributed By: James A. Oliver Microsoft ® Encarta ® 2009. © 1993-2008 Microsoft Corporation. All rights reserved.