flying squirrel, name for certain nocturnal tree squirrels adapted for gliding; they do not actually fly. Most are found in Asia, but one species of the genus Pteromys extends into SE Europe and the two species of Glaucomys are found in North America. The gliding mechanism is a fold of furry skin extending along each side of the body from the wrist to the ankle and, in some species, to the tail. When the animal is at rest the flaps are folded; when it stretches its limbs for leaping, as do all tree squirrels, the flaps are stretched out taut like a parachute. The tail in many species is broad and flat, with a flat row of hairs on either side. The animal uses movements of the flaps, limbs, and tail to control direction. The glide always starts from a high tree branch; if it is a long glide the animal comes to rest near the ground and must climb up again. The small North American flying squirrels leap from heights of 50 ft (15 m) or more and may travel a horizontal distance of over 100 ft (30 m). Flying squirrels are seldom seen because of their nocturnal habits and high dwelling places. They nest, often many together, in holes in trees. They feed on a variety of plant matter, as well as on insects. The North American flying squirrels, found in forested regions over much of the continent, have soft, thick, brownish fur. The northern species, Glaucomys sabrinus, of Canada and the NE and W United States, is up to 12 in. (30 cm) long including the tail, which is nearly as long as the head and body; it weighs 4 to 61/2 oz (110–180 grams). The southern species, G. volans, of the eastern half of the United States and parts of Mexico and Guatemala, is slightly shorter and weighs about a third as much. Most Old World species are similar, but the giant flying squirrels, genus Pteromys, of S Asia, are up to 4 ft (120 cm) long and may be observed sleeping on branches during the day. The scaly-tailed squirrels, or African flying squirrels, are not true squirrels, but members of a separate rodent family (Anomaluridae). Found only in tropical Africa, they are anatomically quite different from the true flying squirrels and include both gliding and nongliding species. Flying squirrels are classified in the phylum Chordata, subphylum Vertebrata, class Mammalia, order Rodentia, family Sciuridae.