The beaver is a medium-sized mammal. They have thick fur, large front teeth and a long flat tail. They are three to four feet long, which includes a nine inch tail, and weight 40-60 pounds. They use their tail for steering in the water and balancing on land. This creature can only be found in a few places in the world, including North America, Scandinavia, Russia and Geneva. It is the largest rodent in North America and the second largest in the world. Beavers build dams in rivers and streams to create a pond from small trees and mud. Then they build lodges, which looks like a pile of wood, with the entrance under the water which keeps out other animals. These animals might live for ten to twelve years. They young will live with their parents for about two years. They eat bark, water plants, berries and fruit. They must store an underwater food cache in order to survive the winter. These creatures are slow and clumsy on land, easy prey for predators such as wolves, lynx, wolverines and bears. Years ago, humans trapped them for their fur, musk glands and tail. People wore the fur and made perfumes and medicines from the musk glands. These animals are very good swimmers and can stay under water for about fifteen minutes. They mate for life and are very social animals, living and working together in family units. Their large front teeth help them chew through the bark of trees, both to build their lodge and dam, and to eat tree bark.