Between 54 and 37 million years ago, the first squirrels were running around the "steamy North American habitat with hulking rhinos and tapirs, dainty wild horses, hyenas, and lemur-like primates" (Youth 2). Now, millions of years later, squirrels are found on every continent except Antarctica and Australia. With sizes ranging from the three-foot long giant squirrel of Asia to the Amazonian pygmy squirrel, the rodent order makes up a large part of the approximately 4,600 mammals (Youth).

Members of the Sciuridae family in North America can be divided into three groups--ground squirrels, tree squirrels, and flying squirrels. The following list provides examples for each of these groups:

Ground squirrels

Eastern Chipmunk (Tamias striatus), Thirteen-lined ground squirrel (Spermophilus tridecemlineatus), Richardson's ground squirrel (Spermophilus richardsonii), Golden-mantled ground squirrel (Spermophilus lateralis)

Tree squirrels

Eastern gray squirrel (Sciurus carolinensis), Western gray squirrel (Sciurus griseus), Arizona gray squirrel (Sciurus arizonensis), Fox squirrel (Sciurus niger), Abert's squirrel (Sciurus aberti), Douglas' squirrel (Tamiasciurus douglassii), Red squirrel (Tamiasciurus hudsonicus)

Flying squirrels

Northern flying squirrel (Glaucomys sabrinus), Southern flying squirrel (Glaucomys volans)

Squirrel diets can include nuts (The hickory, walnut, pecan, hazelnut, chestnut, beechnut, and acorn are native to North America.), pinecones, seeds, flowers, fruits, and fungi.

Tree squirrels and flying squirrels live in tree cavities or in the nests they build, which are called dreys. The tree cavities are lined with shredded bark and other plant material. Dreys are made of leaves, twigs, and any other material available, including hair and Christmas decorations. They can be located in the fork of a tree or on the tree's outer branches. Ground squirrels generally live in burrows underground.

Teeth

The word rodent originates from the Latin rodere meaning "to gnaw" (Youth 2). If squirrels did not gnaw on objects, their teeth would continue to grow until they punctured their skull, which would result in death.

Eyes

As a result of the placement of their eyes, squirrels have a wide range of vision, useful for spotting predators. However, since the optic nerve enters the back of the eye, squirrels have a small blind spot.

It is very important to be able to judge distance so squirrels can accurately leap from branch to branch. "Squirrels often shift their head from side to side or up and down just before jumping, gathering additional visual information about the distance involved" (Long 72).

While squirrels have a difficult time focusing on things that are up close (fingers can be mistaken for peanuts!), one study shows that squirrels were able to recognize other squirrels up to 50 feet away (Long 72).

Studies have also shown that squirrels are possibly color blind (Long 72).

Ears

Squirrels must have an acute sense of hearing so they can hear predators such as hawks and house cats. Ear tufts seen on red squirrels and others provide protection from the cold.

Smell

The sense of smell is crucial to finding their hidden caches. Squirrels can also detect whether or not a nut has been spoiled by pests, such as insects that have bored their way into the center of the nut.

Feet

The front paws have four digits, while the back paws have five. Squirrels can rotate their hind legs to hook their claws onto a surface; this allows them to vertically descend.

Fur

Most squirrels shed their coat twice a year, once in the spring and once in the fall. Their fur is multi-layered; the inner coat is thick and insulated. "Extra-sensitive hairs called vibrissae form whiskers that add additional sensory capabilities, of particular use to the squirrel in dark nests and tree cavities" (Long 77).

Tail

The word squirrel comes from the Greek syllables skia meaning "shadow" and oura meaning "tail" (Long). This tail is used for many purposes such as protection from the elements, balance on skinny branches and power lines (yikes!), and signaling.

Burt & Grossenheider. A Field Guide to the Mammals. Boston: Houghton Mifflin Company, 1952.

Complete Field Guide to North American Wildlife: Eastern Edition. New York: Harper & Row, 1981.

Long, Kim. Squirrels: A Wildlife Handbook. Colorado: Johnson Books, 1995.

Webster, Parnell & Biggs. Mammals of the Carolinas, Virginia, and Maryland. Chapel Hill: The University of North Carolina Press, 1985.

Youth, Howard. Enjoying Squirrels More (or Less!). Ohio: Pardson, 1997.