BOA, a name formerly applied to all large serpents which, devoid of poison fangs, kill their prey by constriction; but now confined to that subfamily of the Boidae which are devoid of teeth in the praemaxilla and are without supraorbital bones. The others are known as pythons (q.v.). The true boas comprise some forty species; most of them are American, but the genus Eryx inhabits North Africa, Greece and south-western Asia; the genus Enygrus ranges from New Guinea to the Fiji; Casarea dussumieri is restricted to Round Island, near Mauritius; and two species of Boa and one of Corallus represent this subfamily in Madagascar, while all the other boas live in America, chiefly in tropical parts. All Boidae possess vestiges of pelvis and hind limbs, appearing externally as claw-like spurs on each side of the vent, but they are so small that they are practically without function in climbing. The usually short tail is prehensile.
One of the commonest species of the genus Boa is the Boa constrictor, which has a wide range from tropical Mexico to Brazil. The head is covered with small scales, only one of the preoculars being enlarged. The general colour is a delicate pale brown, with about a dozen and a half darker cross-bars, which are often connected by a still darker dorso-lateral streak, enclosing large oval spots. On each side is a series of large dark brown spots with light centres. On the tail the markings become bolder, brick red with black and yellow. The under parts are yellowish with black dots. This species rarely reaches a length of more than 10 ft. It climbs well, prefers open forest in the neighbourhood of water, is often found in plantations where it retires into a hole in the ground, and lives chiefly on birds and small mammals. Like most true boas, it is of a very gentle disposition and easily domesticates itself in the palm or reed thatched huts of the natives, where it hunts the rats during the night.
The term “boa” is applied by analogy to a long article of women’s dress wound round the neck.