Beaver. The Body of a Beaver

Beaver is a furry animal with a wide, flat tail that looks like a paddle. Beavers are known for their skill at cutting down trees with their strong front teeth. They eat the bark and use the branches to build dams and lodges (homes) in the water. Beavers almost always seem to be busy working. For this reason, we often call a hard-working person an "eager beaver" or say that the person is "busy as a beaver."

Beavers live in rivers, streams, and freshwater lakes near woodlands. They are excellent swimmers and divers. A beaver can swim underwater for ½ mile (0.8 kilometer), and can hold its breath for 15 minutes.

There are more beavers in the United States and Canada than anywhere else in the world. Beavers are also found in Asia and Europe. In the 1980’s, trappers in the United States and Canada captured about a million beavers a year. Beaver fur is soft and shiny, and it wears well. Clothing manufacturers use it to make fur coats and to trim the collars and cuffs of cloth coats. Beaver fur is also squeezed together with other kinds of fur to make a cloth called felt.

After cutting down a tree, a beaver moves it to a nearby pond

Beavers were probably the most hunted animals in North America from the late 1500's through the 1800's. The pioneers and Indians ate beaver meat, and traded the furs for things they needed. In the late 1600's, a person could trade 12 beaver skins for a rifle. One beaver skin would buy four pounds of shot, or a kettle, or a pound of tobacco. Trading companies shipped beaver fur throughout the world to be made into coats or hats. Hunters killed so many beavers that hardly any were left in North America by the late 1800's. The U.S. and Canadian governments passed laws to protect the animals. Today, beavers, like many other wild animals, can be trapped only at certain times of the year.

The body of a beaver. North American beavers are 3 to 4 feet (91 to 120 centimeters) long, including the tail, and weigh from 40 to 95 pounds (18 to 43 kilograms). They are the largest rodents (gnawing animals) in the world except for the capybara of South America. Unlike most other kinds of mammals, beavers keep growing throughout their lives. Most beavers look larger than they really are because of their humped backs and thick fur. Thousands of years ago, some beavers of North America were about 7 ½ feet (2.3 meters) long, including the tail—almost as long as the grizzly bears. No one knows why these huge beavers disappeared.

Head. The beaver has a broad head, with large and powerful jaws. Its rounded ears and small nostrils can close tightly to keep water out. A beaver has three eyelids on each eye. Two outer eyelids, one upper and one lower, fit around the eye. A transparent inner eyelid slides down over the eye and lets the animal see under water. On land, it protects the eye from sharp twigs when the animal cuts trees. The beaver cannot see well, and depends on its keen hearing and smell to warn it of danger.

Teeth. A beaver has 20 teeth—4 strong, curved front teeth for gnawing, and 16 back teeth for chewing. The front teeth, called incisors, have a bright orange outer covering that is very hard. The back part of the incisors is made of a much softer substance. When a beaver gnaws, the back part of its incisors wears down much faster than the front part. As a result, these teeth have a sharp, chisel-like edge. The incisors never wear out because they keep growing throughout the animal's life. The back teeth have flat, rough edges and stop growing when the beaver is about 2 years old.

There are large gaps between the beaver's incisors and its back teeth. Flaps of skin, one on each side of the mouth, fold inward and meet behind the incisors. These skin flaps seal off the back of the mouth. They let the animal gnaw wood on land or in the water without getting splinters or water in its mouth. The flaps open when the beaver wants to eat or drink.

Feet. The beaver's legs are short, and its feet are black. Tough skin, with little hair, covers the feet. Each front paw ends in five toes that have long, thick claws. A beaver uses its claws to dig up the roots of bushes and trees for food. When swimming, the animal usually makes tight fists of its front paws and holds them against its chest. Sometimes, when a beaver swims through underwater brush or grass, it uses its front paws to push the plants aside.

The back feet are larger than the front ones, and may be 6 to 7 inches (15 to 18 centimeters) long. The toes are webbed and end in strong claws. Two claws on each foot are split. The beaver uses these split claws to comb its fur. The webbed feet serve as flippers, and help make the animal a powerful swimmer and diver.

Tail of a beaver is one of the animal's most interesting features. The stiff, flat tail looks like a paddle. It is about 12 inches (30 centimeters) long, 6 to 7 inches (15 to 18 centimeters) wide, and ¾ inch (19 millimeters) thick. A small part of the tail nearest the beaver's body has the same kind of fur as the body. The rest is covered with black, scaly skin and has only a few stiff hairs. The beaver uses its tail to steer when it swims. The tail is used as a prop when the animal stands on its hind legs to eat or to cut down trees. A beaver slaps its tail on the water to make a loud noise to warn other beavers of danger.

Fur. Beaver fur varies from shiny dark brown to yellowish brown. It looks black when wet. A beaver's coat consists of two kinds of fur: (1) short, soft underfur; and (2) long, heavy guard hairs. The guard hairs lie over the underfur and protect it. The underfur helps keep a beaver comfortable in the water. This fur traps air and holds it close to the animal's skin. The trapped air acts as a protective blanket that keeps the beaver warm, even in icy water.