Squirrels are rodents. All rodents are characterized by the presence of chisel-like gnawing teeth that grow constantly, and the squirrel family of rodents is called Sciuridae.
Squirrels come in three basic forms: flying, tree and ground. Tree squirrels are basic squirrels that have large bushy tails and live in trees. Flying squirrels have a membrane running from their front legs to their back legs that they use to glide from tree to tree. Ground squirrels live in holes in the ground. The ground squirrel family includes chipmunks, marmots and prairie dogs. Most types of squirrels are active during the day. Flying squirrels, however, tend to be nocturnal.