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 have two subfamilies: Boinae or true boas and Erycinae or sand boas. Pythons are sometimes classified as a subfamily of Boidae, but are frequently listed under their own family, Pythonidae.
True boas are medium-sized to large snakes. It used to be said that boas were New World Snakes and pythons were Old World Snakes, but, with boas found on Madagascar and the Solomon Islands, this is not quite true. Instead, it is possible that boas have survived in evolutionarily isolated areas. South America, until a few million years ago, had a distinct fauna that included marsupial mammals; with the land bridge to North America, boas have migrated north as placental mammals and colubrids (for example) have migrated south.
Compared to true boas, erycines are quite small, with most members of this subfamily remaining well under a metre 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.
- Calabaria reinhardtii (Calabar Burrowing "Python", Africa; sometimes equated with Charina)
- Charina bottae (Rubber Boa, west coast of North America)
- Eryx (Sand Boas, Africa, western Asia and southeastern Europe)
- Lichanura trivirgata (Rosy Boa, southwestern U.S. and northwestern Mexico; sometimes equated with Charina)
- The Sand Boa Page (http://www.kingsnake.com/sandboa/)