Squirrels are rodents, which means their teeth continue to grow throughout their lives. This allows squirrels to eat diets of nuts, roots and other fairly rough vegetable material without their teeth being worn down. However, squirrels are opportunistic and also eat insects, bird eggs and even nestlings.
Squirrels live all over the world with the exception of Antarctica and Australia. They are mostly small mammals, though the Indian giant squirrel can grow to 3 feet in length.
Biologists believe there are about 200 species of squirrels and separate them into ground squirrels and tree squirrels. Tree squirrels include the familiar gray squirrel, while ground squirrels include marmots such as the yellow-bellied marmot. Another type of squirrel is the flying squirrel, which doesn't really fly but glides with the help of membranes of skin that join their limbs to their bodies. A gathering of squirrels is called a dray or a scurry.
Squirrels help with the propagation of trees because they bury their food in preparation for winter. This food includes seeds such as acorns. Though the squirrel digs up some of its cache, it doesn't dig up all of the acorns. These forgotten acorns then germinate and grow into oaks.