Beavers are large, aquatic, partly nocturnal rodents. Of the two species, Castor canadensis is the North American beaver which lives in the woodlands from northern Mexico to Alaska and Canada. It once had been overtrapped to the point of confining it to a far western habitat, but the beaver now has returned to eastern regions. It has chisel-like front teeth that enable it to gnaw down trees for building dams, island lodges, and canals. Their lodges have underwater entrances to keep out predators, with a large dry room inside that is used as a nursery and haven. Beavers float small trees and branches through canals to the stream where they are building. They feed on marsh grasses, roots, barks, and twigs.