Boas are concentrated in the tropical and subtropical Americas, with relatives in Africa, Asia and the Pacific islands. Only two lineages reach the United States, both in the arid west, and both are small, secretive and slow.
Lichanura trivirgata is a stocky boa under a metre long, striped lengthwise in rose, brown or grey, that shelters among boulders in desert canyons and emerges at dusk to hunt woodrats, mice and young rabbits. It kills by constriction and bears live young. The rubber boas, genus Charina, are the northern counterparts: blunt, smooth, plain-brown snakes, one of which reaches southern British Columbia and is among the most cold-tolerant boas in the world.
The species count is unsettled. Current checklists also recognise the northern three-lined boa, Lichanura orcutti, and the southern rubber boa, Charina umbratica, of the southern Californian mountains, so the country holds two boa lineages but somewhere between two and four species. The rubber boa presents its blunt tail as a decoy head when threatened, and older animals often carry a scarred tail as evidence.