CLASSIFICATION
Boa is the common name for about 6 genera and 50 species of SNAKES that constitute the family Boidae. Closely related to PYTHONS, the family includes the largest of all snakes, the water-dwelling ANACONDA of South America. All boas are nonpoisonous and kill by constriction; unlike the pythons, they bear live young. Most boas are active at night and have pits along their lips that are sensitive to the heat of prey. The snakes are usually handsomely marked and often iridescent, the most striking being the rainbow boa, Epicrates cenchis. The species best known as "boa" is the boa constrictor, Constrictor constrictor, which ranges from Mexico to Argentina and the West Indies. The snake grows up to 3.7 m (12 ft) long, but a 5.6-m (18.5-ft) specimen is on record. In the pet trade this snake is often called a "red-taile" boa because of its reddish brown markings on its tail.
Boas are primitive snakes with anatomical features that reflect their lizard ancestry, such as bony vestiges of hind limbs that terminate in external claws, and the presence--except in the woodsnakes--of two functional lungs instead of the one found in most snakes.
The typical boas are ground or tree dwellers of tropical America and the island of Madagascar, whereas the sand boas are semidesert burrowing snakes of northern Africa and southern Asia. The two North American boas--the rosy and the rubber boa--resemble the sand boas.
Red-tail boas have cryptic coloration, and blend in very easily will fallen leaves on the ground. Although they can easily climb trees in the understory and canopy of the rainforests, and indeed do so to search for food, they retire to the forest floor where they're very well camouflaged. Snakes in general, lack external ear openings, eardrums, and middle-ear cavities. The small, sound-conducting columella bone, however, is still present. In other reptiles the columella is positioned between the inner ear and the eardrum, but in snakes it is situated between the inner ear and the jaw hinge (quadrate bone). When the snake's head is on the ground, earthborne sounds or vibrations are picked up by the lower jaw and skull and are transmitted by bone conduction to the columella and through the columella to the inner ear. Snakes, therefore, can readily detect earthborne sounds. The lack of eardrums and middle-ear cavities implies that snakes cannot hear airborne sounds. Certain experiments, however, have shown that the snake's inner ear does respond to low-frequency airborne vibrations Snakes can detect heat, or infrared, rays through specialized groups of nerve endings scattered through the skin. These heat receptors are presumably involved in sun basking and other thermoregulatory behaviors. More specialized heat receptors are present as pits along the upper lip margins of many pythons and boas.
The snake's skin is primarily a protective structure, guarding it against physical injury and the loss of body moisture (desiccation). The scales covering the skin are epidermal, that is, they are mainly derived from a folding of the epidermis, or the upper layer of the skin. Because the scales do not increase in size or because the outer layer becomes worn, or because of reasons not yet understood, a snake must periodically shed its old skin and replace it with a new and larger one. In molting, the old, upper layer of the epidermis becomes loosened and separated from a newer layer of the epidermis developing beneath it. The molting process, or ecdysis, is accomplished by the snake loosening the skin around the lips, pushing this back, and crawling out of the old skin, turning it inside out. Frequency of molting, or shedding, varies according to the growth rate of the snake.
The boa constrictor, C. constrictor, is a New World snake that kills rodents and other small animals by striking and coiling around its victim with incredibly fast movements. Once wrapped around its prey, the boa constrictor tightens its coils, preventing the animal from breathing. It then swallows its meal whole.
Some snakes simply suffocate their captured prey by squeezing them with their jaws, but a snake's long, muscular body is ideally suited for applying pressure on a prey animal. Constriction has been defined as the immobilization of prey by the exertion of pressure by two or more points of the snake's body. Constriction does not crush the prey animal but rather prevents it from breathing and suffocates it. In the case of very small animals with a high metabolic rate and the need of an uninterrupted supply of oxygen, death may be very quick. In larger, stronger animals, however, it may be quite slow. It is also relatively slow in cold-blooded prey, such as lizards. Such animals, however, often become torpid and are swallowed alive. Some snakes use one or two body loops to press their prey against the ground or against the inside of a burrow if below ground. Others wind or wrap around their prey.
Partly as an adaptation to permit the swallowing of large food items whole, the snake's skull has been increasingly modified for greater elasticity. In many evolutionarily advanced snakes the only solid portion of the skull is the brain case, the upper skull consisting broadly of the brain case in the rear; small protective bones around the eyes and snout in front; and four rather long tooth-bearing bones below. All four tooth-bearing bones are loosely attached to the skull by elastic ligaments and are independently movable. The bones of the snout are also movable and allow the snake to bend its snout upward.
Each side of the lower jaw bears a row of teeth, and the two halves of the lower jaw are not rigidly fused where they meet in front; rather, they are united only by elastic ligaments that permit the two halves to be rotated or moved apart. A snake can separate its upper and lower jaws, and also the two halves of its bottom jaws to swallow prey over three times larger than its self.
Snakes have powerful digestive enzymes (specialized proteins) to break down the hair, feathers, bones, and other parts of their prey. As part of the digestive system, the salivary glands of the mouth also produce powerful enzymes. If saliva containing these enzymes enters the wounds of a prey animal, it not only begins the digestive process but also may cause such serious tissue damage that the prey dies. Such toxic elements have been found in the saliva of many nonpoisonous snakes, and they are generally introduced into the prey's wounds by repeated bitings by the snake.
In the wild. boas reach sexual maturity at two or three years and breed during the rainy season. If fed appropriately, most captive- rasied boas will become sexually mature by the end of their third year. Once conception has occured, boas usually remain pregnant of "gravid" for 4 to 10 months and then give birth to live young called neonates. They hold approximately 20 to 60 eggs internally until they hatch and then the hatchlings and the leathery shells are expelled from the mother snake. Neonates weigh approximately 2 to three ounces, are 14-22 inches in length, and will eat soon after their first shed--about one week after birth.
Boas are among the longest lived of all snake species. Reports of longevities in excess of twenty years are not uncommon. There is a record of a specimen at the Philadelphia Zoological Gardens which lived for 40 years, 3 months and 14 days.
All pythons and boas are considered as threatened by the Convention on the International Trade in Endangered Species. This means that special permits will be required for the import/export of animals between countries. Numbers are dropping due to habitat destruction, and although protected over much of its range, many skins are sold to the leather trade every year.
Grolier's Encyclopedia
Vosjoli, Philippe de. The General Care and Maintenance of Red-Tailed Boas
Wildlife Fact File
