Flying squirrels cannot fly, but they steer with a wingtip found nowhere else
No flying squirrel has ever flapped its way into the air. What the 50 species do instead is glide, sometimes as far as 90 metres, on a furry membrane stretched from wrist to ankle. And in 2019 someone noticed by accident that North American species glow pink under ultraviolet light, for reasons nobody yet understands.
The gliding membrane, called a patagium, works like a parachute, while the long tail adds stability. The real control comes from the wrist. A spur of cartilage projects from it and is held upward during a glide, forming a wingtip that can tilt to different angles and tighten or slacken the membrane. This styliform cartilage exists only in flying squirrels, not in other gliding mammals, and probably evolved from wrist bones that ordinary squirrels also have.
Molecular studies settled a long argument about their origins: flying squirrels share a single common ancestor, arose roughly 18 to 20 million years ago and are the sister group of tree squirrels. Compared with similar-sized relatives they have longer forearms and lower backbones but shorter hands, feet and tail vertebrae, proportions that lighten the load on the membrane and improve agility in the air. The trade-off is that they are clumsier on the ground.
Why glide at all? One idea is economy: sailing between trees costs less energy than climbing down, crossing the forest floor and climbing up again, so a squirrel can forage over more ground. Another is safety, both escaping predators and landing gently. Approaching a trunk, the animal pitches up sharply, bleeding off speed so all four legs can absorb the impact, and a misjudged jump can be corrected mid-air.
Most species are active at night and eat almost anything from seeds, fungi and tree sap to insects and birds' eggs. Babies are born naked and helpless, begin practising glides at about five weeks and leave the nest at around ten. The New World genus Glaucomys means gleaming mouse, while the Old World Pteromys means winged mouse; the Siberian flying squirrel ranges west into Finland and Estonia.
Source: Flying squirrel
