Beaver (Castor canadensis)

 Beaver, semi-aquatic rodent noted for the building of dams. They are large rodents; the average adult beaver weighs about 16 kg (about 35 lb), but specimens as heavy as 40 kg (90 lb) have been found, and some extinct beavers were even larger.

The beaver is usually about 76 cm (about 30 in) long and stands less than 30 cm (12 in) high. The broad, flat, scaly tail is about 25 cm (about 10 in) long and serves as a warning signal when slapped against the water, as a support when the beaver is standing on its hind legs, and as a rudder while swimming. The body is plump, the back arched, the neck thick, the hind feet webbed with claws. The fur is usually reddish-brown above and lighter or grayish below. The eyes are small and the nostrils closable. The two front teeth on either jaw are like those of other rodents, wearing away more rapidly behind so as to leave a sharp, enameled chisel edge. With these, the beaver can cut down large trees for dam building. The animals mate for life and may live 20 years or more. The female has one litter a year, usually of two to four young.

Beavers have long been exploited for their fur, and for many years during the 18th and 19th centuries hundreds of thousands of beaver skins were exported to Europe from North America annually. The animals were also sometimes destroyed because of the damage they did to forests and the flooding occasionally caused by dams. Ceaseless slaughter led to near extinction of beavers in both Europe and North America. The beaver is still almost extinct in Europe, but is becoming reestablished in Canada and in protected areas of the United States. Beavers are sometimes viewed as pests, particularly in suburban areas of the eastern United States. Several states have limited trapping seasons.