Flying squirrels are mammals equipped for gliding rather than true flight, using a specialized skin membrane to leap and sail from tree to tree. The question of their size is complex because the more than 50 species worldwide exhibit a dramatic range of body dimensions. This variability means a single measurement cannot accurately represent the entire group, which includes species the size of a small mouse and others comparable to a domestic cat. Their overall dimensions are complicated by the unique anatomy that allows them to glide.
Standard Dimensions of Flying Squirrels
The size of flying squirrels spans a considerable range in both length and mass. A typical adult, excluding the largest species, generally measures between 20 to 65 centimeters (8 to 25 inches) in total length, including the head, body, and tail. Body weight ranges from 50 grams (1.8 ounces) up to 2.5 kilograms (5.5 pounds) for the heaviest specimens. The tail contributes significantly to the overall length, frequently accounting for almost half of the total body measurement. This long, flattened tail acts as a dynamic rudder and brake during aerial maneuvers. Most flying squirrels are relatively small rodents adapted for arboreal life.
North American vs. Giant Species Size Differences
The difference in size is best illustrated by comparing the two primary North American species to their Asian counterparts. The Southern Flying Squirrel (Glaucomys volans) and the Northern Flying Squirrel (Glaucomys sabrinus) are diminutive.
An adult Southern Flying Squirrel typically weighs 56 to 85 grams (2 to 3 ounces) and measures 21 to 25 centimeters (8.5 to 9.8 inches) in total length. The Northern species is slightly larger, weighing up to 140 grams (4.9 ounces) and reaching 37 centimeters (15 inches). These North American gliders are comparable in size to a common tree squirrel.
This contrasts sharply with the “Giant Flying Squirrels” (genus Petaurista), primarily found in Asia. These squirrels are substantially larger, with some species reaching body lengths of 30 to 60 centimeters (12 to 24 inches) and tails extending an additional 35 to 64 centimeters (14 to 25 inches). Their mass can be considerable, with the largest individuals weighing between 1 to 2.5 kilograms (2.2 to 5.5 pounds). The largest flying squirrels can have a total length exceeding one meter (over three feet) and a mass akin to a small house cat.
The Gliding Membrane and Perceived Dimensions
The size of a flying squirrel when resting differs significantly from its perceived dimensions while in motion. This expansion is due to the patagium, the expansive, fur-covered membrane of skin that enables gliding. The membrane stretches laterally from the wrist of the forelimb to the ankle of the hind limb on each side of the body.
When the squirrel leaps and extends its limbs, the patagium unfurls, transforming the compact body into a broad, rectangular airfoil. A specialized cartilaginous rod extends from the wrist to support the tautness of the membrane’s leading edge. This structural adaptation dramatically increases the animal’s surface area, which is the functional size that allows it to catch the air.
The expanded patagium creates a gliding surface many times wider than the resting body width. The squirrel adjusts the tautness and shape of this membrane by subtly moving its limbs, allowing for steering and braking. The tail also acts as an aerodynamic rudder to control the glide path and slow descent before landing.