Squirrel is a mammal of the genus Squirrel in the family Squiridae of the order Rodentia.

The body of the squirrel is slender, with longer hind limbs; there are no skin wings between the front and rear limbs, and the limbs are strong; the eyes are big and bright, the ears are long, and there is a tuft of hair at the tip of the ear, especially in winter;

The hair is usually dark brown or auburn in summer, and there is more hair in winter. It is gray, smoky gray, or gray-brown, with white abdominal hair; there are sharp hooks on the fingers and toes, and the tail hairs are numerous and fluffy, often curled toward the back. Female squirrels are slightly heavier than male individuals. Because squirrels look like mice, and most of them like to eat nuts such as pine cones, they are accustomed to living on trees, especially pine trees, hence the name.

Squirrels are generally small in size. They can be as small as the African squirrel, which is 7-10 cm long and weighs about 10 grams, or as large as the marmot (marmot), which is 53-73 cm long and weighs about 5-8 kg. Squirrels have no skin wings between the front and rear limbs and have strong limbs.

The toes have sharp claws with hook-shaped ends. Female individuals are slightly heavier than male individuals. Chipmunks and squirrels have cheek pouches on their cheeks, which can store a lot of food.

Squirrels mostly enter estrus in spring and summer, and the estrus lasts about two weeks. The suitable age for squirrel breeding is 8 to 9 weeks for females and 9 to 10 weeks for males.

The pregnancy time of squirrels is about 35 to 40 days, and they can give birth to about three babies per year, with 4 to 6 babies being born each time. Newborn squirrels are tiny and cannot see, so they rely on their mother's milk for all their nutritional needs. Squirrels develop very slowly and do not open their eyes until nearly 30 days after birth. It is not until one and a half months old that the squirrels are willing to go outside for activities.

Squirrels mainly feed on food rich in carbohydrates, protein, and fat, which may be an essential reason why they sleep for about 14 hours a day. In addition, squirrels, golden hamsters, and stoats sleep for this long every day. The former sleeps in caves during the day, hiding from predators. Although they sleep long, they are highly active when awake. They sleep nearly twice as long as we humans do every day.

Squirrels are widely distributed in Asia, North and South America, and Europe. Squirrels live in a variety of habitats, from tropical rainforests to north temperate coniferous forests, tundra, and alpine meadows to semi-arid deserts, agricultural lands, and city parks; some species are arboreal, living on tree branches and in tree cavities. They make nests in them; some are terrestrial and dig burrows underground.