Rodent, a gnawing mammal. There are more species of rodents, and probably more individuals, than there are of all other mammals combined. They include beavers, chipmunks, mice, porcupines, rats, and squirrels. Rodents breed so swiftly that they would soon overrun the earth if they were not the prey of almost all flesh-eaters. Most rodents are small fur-bearing animals, although some, such as the porcupine, develop spiny quills. Some, such as beavers and muskrats, are prized for their fur.

SquirrelsSquirrels are common rodents.

Rodents, unlike other mammals, have only two pairs of incisors (front teeth)—one upper pair and one lower pair. The incisors grow throughout life. Gnawing grinds the edges into a chisel shape. Rodents have no canine teeth. In many species, the gap between incisors and molars is filled by a hairy pad that prevents inedible gnawed material, such as wood chips, from entering the mouth cavity by keeping it between the mouth walls and the teeth. Many rodents have cheek pouches, which they use for carrying food.

Most rodents are burrowing animals, but some live in trees and others spend much of their time in water. Almost all are vegetarians; some, such as squirrels, eat both plants and animals.

As a group rodents are destructive pests. They destroy grains and other foods, ruin land with their burrows, and carry various kinds of diseases.

Rodents form the order Rodentia of the class Mammalia.