Trap-Door Spider, common name for any of several large, hairy, harmless tropical spiders that nest underground. They make long burrows in the earth, line them with silk, which they spin, and fashion at the entrance a bevel-edged, hinged, accurately fitting trapdoor often made of alternate layers of earth and silk. The upper surface of the door may be covered with earth or gravel, thus disguising the entrance. A species common in the southwestern United States digs holes about 2.5 cm (about 1 in) in diameter and sometimes 30 cm (12 in) in length.
The nests of trap-door spiders are generally in groups. The young hatch in the burrows of their mothers and live there for a few weeks; they then leave the nest and begin small underground burrows of their own. Trap-door spiders subsist largely on ants and other insects.

Scientific classification: Trap-door spiders make up the family Ctenizidae of the order Araneae. The species common in the southwestern United States is classified as Bothriocyrtum californicum.

That's all well and good, but I think I'll just do my best to avoid getting bitten. Which is generally good advice anytime, but particularly so with something large enough to catch and eat small frogs and lizards.

Yikes!!!!! I hope I never run across one in my garden. I know they are supposed to be great predators and kill pests, but...... I HATE SPIDERS!
The whole indea of wrapping up their prey injecting them with digestive enzimes and sucking out the resulting meal, makes me think of Dracula (:-o