BEAVER, a large, aquatic, gnawing mammal (see RODENTIA), recognized by its large, flat scaly tail. The Old World beaver (Castor fiber) is found in Europe and northern Asia ; the very similar American beaver (C.
canadensis), differs chiefly in the form of the nasal bones of the skull. The beavers form the f am ily Castoridae, in which the hind feet are webbed and the claw of the second hind toe is double.
The present day species are both about 3 ft. long, of which nearly one-third is tail. The valuable fur is composed of two kinds of hair—one close-set, silky and grey; the other coarser, longer and reddish-brown. Formerly com mon in England, the European beaver is now confined to the Elbe, the Rhone and Scandinavia. The American species has also greatly decreased in numbers.
Beavers are gregarious, living in small streams, where, to ren der the water of sufficient depth to prevent its freezing to the bot tom, they build dams of mud, stones and tree trunks. These structures are frequently of great strength and show considerable ingenuity. In the pools made by the dams the American beavers build "lodges," chambers opening under water and formed of the same materials as the dam. Both dam and lodge are built in the autumn, and the lodge is covered on the outside with mud, which freezes as hard as stone and is an efficient protection against wolves and other enemies.
The favourite food of the American beaver is the root of the water-lily but it will also eat bark, leaves and berries. When the ice breaks in spring, the beavers leave their lodges and lead a roving life. The flesh of the beaver resembles pork in flavour.
Fossil remains of beavers occur in peat in Europe generally, while in the Pleistocene of England and Siberia are found the bones of a giant extinct form, Trogontherium cuvieri.