The family 'Sciuridae' includes tree squirrels, ground squirrels, and flying squirrels. Tree squirrels have long, bushy tails, sharp claws and large ears. Some have well-developed ear tufts. Flying squirrels have a furred membrane ('patagium') extending between the wrist and ankle that allows them to glide between trees. Ground squirrels are generally more robust than tree squirrels and often have short, sturdy forelimbs that are used for digging. Their tails, while fully furred, generally are not as bushy as those of tree squirrels.

Squirrels are a hugely abundant and well distributed family of rodents that can be found all over the world.

Some varieties like ground squirrels live in massive colonies and burrow underground for safety, while others spend most of their time up in trees. An interesting feature of the squirrel family is that many of them have an extremely well developed vocal alarm system with calls they use to warn each other of danger.

More Info: animaldiversity.org