|Eastern Gray Squirrel, Sciurus carolinensis|
Squirrels are native to the Americas, Eurasia, and Africa, and have been introduced to Australia. The earliest known squirrels date from the Eocene and are most closely related to the mountain beaver and to the dormouse among living rodent families.
Most squirrels are omnivores; they eat anything they find. Many kinds of squirrels live in trees, so they often find nuts. They eat seeds, berries and pine cones too. Sometimes they eat bird's eggs and insects. Most tree squirrels store food in the fall, to eat in the winter. Ground squirrels do not store food. They hibernate which means they spend winter in a deep sleep.
The most common European squirrels are red or brown in color, while common American squirrels are grey or black. Grey squirrels have been introduced from America into Europe (most notably, Great Britain).
The greys carry a virus to which they are immune, but which is deadly to red squirrels. They have taken over most of the red squirrels' territory in deciduous forest. This has greatly reduced the red squirrel's population. Red squirrels still enjoy dominance in the pine forests of northern Britain, but they are now rare in southern areas.
Squirrels breed in February and March in winter, and in June and July in summer. Females may become pregnant up to twice a year. Usually four to six young are born, after a gestation period (pregnancy) of around thirty-nine days. Only the mother looks after the young, which are born completely helpless. Young squirrels are deaf and blind during the first few weeks of their life.
- BBC 3003. Virus threatens UK's red squirrels. BBC News. 
- "Captured squirrels live to nibble again | The Times". Retrieved 2013-04-08.
- "Control of invasive non-native species - Grey Squirrels". Retrieved 2013-04-08.
- Thorington, Richard W.; Koprowski, John L.; Steele, Michael A.; Whatton, James F. (2012). Squirrels of the World. Johns Hopkins University Press. p. 12. ISBN 1421404699.