Flying squirrels move effortlessly through the forest canopy. These creatures are not true flyers like birds or bats, but master gliders, using an adaptation to navigate their arboreal homes. They are primarily nocturnal rodents, with large eyes that help them see in low light conditions as they forage for food. Their nighttime activity means their presence often goes unnoticed.
Measuring Their True Size
The body size of flying squirrels varies by species. In North America, the two most common species are the Southern and Northern flying squirrels. Southern flying squirrels (Glaucomys volans) are smaller, with a body length of 8.3 to 10 inches (210-255 mm), including their tail. They weigh 1.6 to 2.5 ounces (45-82 g). Northern flying squirrels (Glaucomys sabrinus) are slightly larger. Their total length, including the tail, spans 10 to 15 inches (25-37 cm), and they weigh 2 to 4.9 ounces (75-139 g). These measurements represent the squirrel’s physical body, distinct from the expansive membrane that aids their gliding.
The Role of Their Gliding Membrane
A defining feature of flying squirrels is the patagium, a specialized furred membrane stretching from their wrists to their ankles. This membrane functions as a parachute, allowing them to glide effectively between trees. When preparing to glide, a squirrel launches from a high point and extends its limbs, spreading the patagium to create an aerodynamic surface. Cartilaginous extensions from the wrist and ankle bones support the patagium during the glide. While airborne, the squirrel controls its direction and descent rate by making subtle adjustments with its limbs and tail. This membrane, though making the squirrel appear larger during a glide, is an extension for locomotion and does not contribute to its actual body length or weight.
Size Differences Among Species
Over 50 species of flying squirrels exist globally, exhibiting considerable size variation. While North America has smaller species like Glaucomys volans and Glaucomys sabrinus, other regions host much larger or smaller flying squirrels. For example, giant flying squirrels of the genus Petaurista, found in tropical India and Southeast Asia, are significantly larger. The Red Giant Flying Squirrel (Petaurista petaurista) has a head-and-body length of 11 to 21.5 inches (28.5-55 cm), with a tail adding 13.4 to 24.8 inches (34-63 cm). Their weight can reach 7.1 pounds (3,200 g), making them heavier than North American species. Conversely, dwarf flying squirrels (Petaurillus) of northern Borneo and the Malay Peninsula are among the smallest, with bodies measuring just 2.8 to 3.5 inches (7-9 cm) long.