Beavers and their dams play an important role in nature. Because of the dramatic effects their dams have on surrounding ecosystems, these mammals are considered a keystone species. By constructing dams they create wetlands -- lush environments which attract fish, ducks, frogs and other creatures. However, beavers can become a big headache for farmers and landowners -- a problem we'll examine later in this article.
Lemming is a small rodent that inhabits northern latitudes. Lemmings grow to a length of six inches (15 cm), including a one-inch (2.5-cm) tail.
Drill is a West African monkey. The animal weighs up to 60 pounds (28 kg), grows up to 38 inches (95 cm) in height is and has a four-inch (10-cm) tail.