BEAVER,  the largest European aquatic representative of the mammalian order Rodentia (q.v.), easily recognized by its large trowel-like, scaly tail, which is expanded in the horizontal direction. The true beaver (Castor fiber) is a native of Europe and northern Asia, but it is represented in North America by a closely-allied species (C. canadensis), chiefly distinguished by the form of the nasal bones of the skull. Beavers are nearly allied to the squirrels (Sciuridae), agreeing in certain structural peculiarities of the lower jaw and skull. In the Sciuridae the two main bones (tibia and fibula) of the lower half of the leg are quite separate, the tail is round and hairy, and the habits are arboreal and terrestrial. In the beavers or Castoridae these bones are in close contact at their lower ends, the tail is depressed, expanded and scaly, and the habits are aquatic. Beavers have webbed hind-feet, and the claw of the second hind-toe double. In length beavers - European and American - measure about 2 ft. exclusive of the tail, which is about 10 in. long. They are covered with a fur to which they owe their chief commercial value; this consists of two kinds of hair - the one close-set, silky and of a greyish colour, the other much coarser and longer, and of a reddish brown. Beavers are essentially aquatic in their habits, never travelling by land unless driven by necessity. Formerly common in England, the European beaver has not only been exterminated there, but likewise in most of the countries of the continent, although a few remain on the Elbe, the Rhone and in parts of Scandinavia. The American species is also greatly diminished in numbers from incessant pursuit for the sake of its valuable fur. Beavers are sociable anirrals, living in streams, where, so as to render the water of sufficient depth, they build dams of mud and of the stems and boughs of trees felled by their powerful incisor teeth. In the neighbourhood they make their "lodges," which are roomy chambers, with the entrance beneath the water. The mud is plastered down by the fore-feet, and not, as often supposed, by the tail, which is employed solely as a rudder. They are mainly nocturnal, and subsist chiefly on bark and twigs or the roots of water plants. The dam differs in shape according to the nature of particular localities. Where the water has little motion it is almost straight; where the current is considerable it is curved, with its convexity towards the stream. The materials made use of are driftwood, green willows, birch and poplars; also mud and stones intermixed in such a manner as contributes to the strength of the dam, but there is no particular method observed, except that the work is carried on with a regular sweep, and that all the parts are made of equal strength. "In places," writes Hearne, "which have been long frequented by beavers undisturbed, their dams, by frequent repairing, become a solid bank, capable of resisting a great force both of ice and water; and as the willow, poplar and birch generally take root and shoot up, they by degrees form a kind of regular planted hedge, which I have seen in some places so tall that birds have built their nests among the branches." Their houses are formed of the same materials as the dams, with little order or regularity of structure, and seldom contain more than four old, and six or eight young beavers. It not unfrequently happens that some of the larger houses have one or more partitions, but these are only posts of the main building left by the builders to support the roof, for the apartments have usually no communication with each other except by water. The beavers carry the mud and stones with their fore-paws and the timber between their teeth. They always work in the night and with great expedition. They cover their houses late every autumn with fresh mud, which, freezing when the frost sets in, becomes almost as hard as stone, so that neither wolves nor wolverines can disturb their repose.
The favourite food of the American beaver is the water-lily (Nuphar luteum), which bears a resemblance to a cabbage-stalk, and grows at the bottom of lakes and rivers. Beavers also gnaw the bark of birch, poplar and willow trees; but during the summer a more varied herbage, with the addition of berries, is consumed. When the ice breaks up in spring they always leave their embankments, and rove about until a little before the fall of the leaf, when they return to their old habitations, and lay in their winter stock of wood. They seldom begin to repair the houses till the frost sets in, and never finish the outer coating till the cold becomes severe. When they erect a new habitation they fell the wood early in summer, but seldom begin building till towards the end of August.
The flesh of the American beaver is eaten by the Indians, and when roasted in the skin is esteemed a delicacy and is said to taste like pork. Castoreum is a substance contained in two pear-shaped pouches situated near the organs of reproduction, of a bitter taste and slightly foetid odour, at one time largely employed as a medicine, but now used only in perfumery.
Fossil remains of beavers are found in the peat and other superficial deposits of England and the continent of Europe; while in the Pleistocene formations of England and Siberia occur remains of a giant extinct beaver, Trogontherium cuvieri, representing a genus by itself.
For an account of beavers in Norway see R. Collett, in the Bergens Museum Aarbog for 1897. See also R.T. Martin, Castorologia, a History and Traditions of the Canadian Beaver (London, 1892).
 The word is descended from the Aryan name of the animal, cf. Sanskrit babhrús, brown, the great ichneumon, Lat. fiber, Ger. Biber, Swed. bafver, Russ. bobr'; the root bhru has given "brown," and, through Romanic, "bronze" and "burnish."
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)