Rodents make up a very large group of mammals. They are usually small animals with short legs. Rodents have many young at once. They also reproduce extremely quickly. Most kinds of rodent that live in cold or temperate lands hibernate in their burrows. All rodents have a pair of long, sharp front teeth, called incisors, on both their upper and lower jaws as well as a set of grinding teeth. These incisors grow constantly and must be kept short by gnawing.

Beavers

Beavers are large rodents. They live in and around rivers that run through dense forests. They feed on twigs, roots and leaves. With their webbed hind feet and broad, flat tails, beavers are excellent swimmers. They use their huge, razor-sharp teeth to gnaw through wood. They fell trees for use in constructing dams to make lakes. The lake around their shelter, or lodge, protects the family from predators.

Capybaras

Capybaras, which measure up to 1.3 metres (more than 4 feet) long and stand 65 centimetres (25 inches) tall, are the largest rodents in the world. Like their relatives, coypus (also called nutria), they are good swimmers and live near water in South America. At the first sight of predators—for example, jaguars, caimans and snakes—they dive into the water and swim away to safety.

Dormouse

Dormice, which are not closely related to mice, are particularly known for their long periods of hibernation. They can hibernate for half the year, or even longer in cooler climates. They sometimes wake for brief periods to eat food from their store collected in the previous summer. Most dormice are good climbers and spend much of their time in the trees, coming out only at night to feed on berries, nuts and insects.

Flying squirrels

Flying squirrels are not true fliers like birds or bats. Instead, they glide between trees, capable of making distances of up to 90 metres (300 feet). Their "wings" are furry sheets of skin that extend from their wrists to their ankles. They also have a fluffy tail, which keeps them stable in flight.

Ground squirrels

Ground squirrels often raise themselves up on their hind legs, watching out for predators. They are mostly herbivorous, but also eat insects and other small invertebrates. They live in underground burrows, often in large numbers.

Jerboa

The jerboa is built for jumping. Its powerful back limbs are four times as long as its front ones. It lives in the deserts of western China and Mongolia. Its large ears help it both listen out for danger and to keep cool in the heat. It does not need to drink since it gets all its water from its food: plants and seeds.

Lemmings

Lemmings feed on grass, leaves, shoots, roots and bulbs in the Arctic tundra. Lemmings migrate in large numbers. They may dive into rivers and lakes as they do so.

Marmots

Marmots, kinds of ground squirrel, live in mountainous areas of Europe, Asia and North America. They feed on grasses, berries, mosses and flowers. They warn other marmots of approaching danger with loud, whistle-like calls. They spend the harsh winters hibernating in their burrows.

Mice

Mice are small rodents with pointed snouts, small, round ears, and long, hairless tails. Though they have poor eyesight, they rely instead on their keen senses of hearing and smell to find food and avoid predators. They are preyed upon by many animals.

Mice can live in almost any environment. Both in the countryside and in towns, mice are often pests, eating crops, causing damage to buildings and spreading diseases.

Muskrat

The muskrat inhabits wetlands of North America. It spends most of its time in the water, eating mostly water plants. In marshy ground, it builds a push-up “lodge”, made from vegetation and mud. Near lakes or rivers, it makes a burrow in the banks.

Porcupines

Porcupines from the Americas live mostly in trees, while those from Africa and Asia are ground-dwellers. All porcupines, however, have sharp spines on their backs. If threatened, they will run backwards into their attackers, leaving several spines stuck in their attackers' skins. Porcupines feed on conifer needles, bark, leaves, buds, roots and berries.

Squirrels

Squirrels are rodents with long, bushy tails. Many kinds of tree squirrel live on farmland, and in parks and cities. During the summer months in the woodlands, tree squirrels feed on fruit and nuts. In autumn, they store seeds and acorns by burying them. They dig them up again in the winter—if they can find them.

Voles

Voles eat small plants, nuts, fruits, roots and bulbs. Mostly tiny burrowers, they are themselves prey for many mammals and birds, especially weasels and owls. The water vole (sometimes called the water rat) is larger than its relatives. It lives in burrows close to streams. An expert swimmer, it feeds on water plants.