Boas are a type of snake that are members of the Boidae family. Boas are basal snakes that are "primitive" in evolutionary terms (i.e. less derived). They are constrictors and give birth to live young. They have anal spurs, a pair of claws on each side of the cloaca which are vestiges of legs. Boas are named after cows (bos) because of the old myth that boa snakes pursue cows and suckle them until they are drained to death.

True boas are medium-sized to large snakes. Females are usually larger than their male counterparts. Boas contain many subspecies based on locality. They include Colombian, Suriname, Bolivian, Peruvian, Hog Island, Long Tail Peruvian, Argentine and more. The boas from the amazon basin are the most colorful possessing bright cherry red tails.

Compared to true boas, erycines are quite small, with most members of this subfamily remaining well under a meter in length. Fossil erycines have been found in rock strata over 50 million years old, and were once widespread in North America. Now, only two species remain in North America, as well as the sand boas in Africa, Asia and southeastern Europe.

At least three erycine species lay eggs: the Calabar Burrowing "Python" , Calabaria reinhardtii (once classified as a python for this reason); the Arabian Sand Boa, Eryx jayakari; and the West African Sand Boa, Eryx muelleri.

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