The average glide of a northern flying squirrel (Glaucomys sabrinusis) is about 65 feet (20 meters), according to the University of Michigan Museum of Zoology, or slightly longer than a bowling lane. But it can go much farther if needed, with glides recorded up to 295 feet (90 meters).

Squirrels can live for up to nine years in the wild, four or five being fairly typical, and the oldest captive specimen on record was a grey squirrel at Wisconsin's Racine Zoo which survived to 23 years and 6 months old.

The smallest squirrel is the African pygmy squirrel. It reaches 2.8 to 5 inches (7 to 13 centimeters) in length and weighs just 0.35 ounces (10 grams).

Ground squirrels and tree squirrels are usually either diurnal (active during the day) or crepuscular (active at twilight), while the flying squirrels tend to be nocturnal (active at night).

Because squirrels cannot digest cellulose, they must rely on foods rich in protein, carbohydrates, and fats.

The word "squirrel" comes from the Anglo-Norman esquirel which is from the Old French escurel, the reflex of a Latin word sciurus, which was taken from an Ancient Greek word meaning "shadow-tailed", a reference to the squirrel's tendency to stand in the shadow of its long, bushy tail.

The best theory as to why the arctic ground squirrel's blood doesn't freeze is that the animal is able to cleanse its body of ice nucleators which are necessary for the development of ice crystals. In the absence of ice nucleators, body fluids can remain liquid while in supercooled state.

Electrical lines are no match for squirrel teeth, which have been blamed for hundreds of power disruptions across the United States, including outages that briefly shut down the NASDAQ stock market in 1987 and 1994. As the Brookings Institution points out, "squirrels have taken down the power grid more times than the zero times that hackers have."

Recent research indicates that squirrels can carry a strain of the bacterium Mycobacterium lepromatosis, the causal agent for Henson's Disease or Leprosy in humans. In fact, scientists now suggest that leprosy may have been proliferated in England during the Middle Ages by the trade of highly prized Viking squirrel pelts.

In 2007, the Iranian army arrested a team of 14 "spy squirrels" found near a nuclear enrichment plant. Officials said they succeeded in apprehending the suspects "before they were able to take any action."