Beavers are rodents and are related to squirrels. They can be up to 75 cm long (Eurasian beaver) or 100 cm long (North American beaver) excluding the tail, and weigh 20 – 30 kg. Their fur is brown and very dense, with 23,000 hairs per square centimetre (humans have 600). Their coat is greased with a fatty substance called castoreum to protect against undercooling. Beavers have streamlined bodies, paddle-like tails and webbing between their digits, so they are well-adapted to life in the water. When they dive they close their nose and eyes and can stay underwater without breathing for 20 minutes.
Beavers always live close to the water where they build their dams and lodges of branches, twigs and mud. An adult beaver can, over one night, use its teeth to cut down a tree that is 50 centimetres in diameter. When a beaver fells larger trees it is only to reach the thinner branches at the top. It cuts entirely through thin trunks and then drags the whole tree to the water. The lodge’s entrance is usually below the surface of the water.
Beavers do not hibernate, instead they are active throughout the year and the young are born in May, up to four at a time. They mainly eat leaves, bark, herbaceous plants and aquatic plants. Beavers live with their partners for life and can be up to 15 years old.
Due to hunting and environmental destruction, the Eurasian beaver vanished from some regions. The last beavers in Sweden were killed in 1871. Norwegian beavers were released into the wild in 1922 and the Swedish beaver population quickly recovered.