Illinois Natural History Survey - University of Illinois

Species Spotlight: Beavers

One of the animal kingdom's most versatile members is a skilled engineer, a tireless lumberjack, and an excellent swimmer; it is also Illinois' largest rodent -- the beaver, Castor canadensis.

Beavers are noted for their construction of dams, which can be deemed a marvel or a nuisance, depending on the location. Beaver dams can flood pastures and roads and destroy timber and trout streams. On the positive side, beaver dams reduce erosion, and the ponds they form can create a habitat for many forms of life: insects lay eggs in them, fish feed on the insect larvae, and many kinds of birds and mammals come to feed and drink.

Near the dams can be found the beaver's lodge, with its living quarters and underwater entrances. These lodges are shared by beaver families. Beavers also live in burrows in the banks of lakes or streams.

The beaver, Castor canadensis.

Beavers mate for life, and their offspring (one to six kits in a litter) will stay with the parents for two years and then go out on their own. Quite a crowd can inhabit a beaver lodge as the parents and as many as a dozen offspring share the lodge in winter and feed from a carefully stored food cache.

Primarily a nocturnal animal, the beaver labors from dusk to dawn on its latest engineering project along a river or stream. The beaver has small eyes, stubby ears, and a stout body. Adults usually weigh from about 25 to 55 pounds. The beaver's coat is dark brown, and its feet and paddlelike tail are black. For protection from chilly water in winter, the beaver has an insulating thick layer of fat beneath its skin.

Beavers build their dams with a foundation of mud and stones, topped by brush and felled branches. Mud and soggy vegetation are used as a plaster to keep it all together. Beavers also dredge canals for easier transportation of dam construction materials. Beavers busily swim about transporting their building materials, including parts of trees they have gnawed with their huge incisors into convenient sizes. The beaver may decide to take a branch with its forefeet and rotate it, chewing off the bark for a snack, much like a human nibbles on an ear of corn. Twigs, leaves, and the bark of trees make up the bulk of a beaver's diet. Water lilies are a special treat.

As it builds a dam, the beaver swims with its webbed hindfeet while its tail serves as a rudder and its forefeet are held close to the chest, free to help hold objects against the chest or to push aside debris. Although the beaver is a graceful, seemingly at-ease worker in water, it will slap the water with its tail when an enemy is spotted and then quickly dive for refuge. On land it is a slow-moving worrier that often interrupts its activities to sniff the air and look for signs of danger.

Because of its valuable pelt, the beaver was trapped almost to the point of extinction in Illinois and other states by the late 1800s. Today's beaver population in Illinois is probably transplanted or emigrated from nearby states. Beavers can be found throughout Illinois and are abundant in many places.

Thomas Rice, Office of the Chief.

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