Strictly speaking, flying squirrels – scientifically known as Pteromyini or Petauristini – cannot really fly, and are gliders not flappers.
Glides of up to 90m have been measured, but not one of this tribe of 43 species has wings or feathers. To understand how flying squirrels evolved, some 18-20 million years ago, you just have to think of normal squirrels leaping from tree to tree. Occasionally a squirrel would be born with slightly more skin under its arms, and this gave it a very small advantage when travelling around the forest. It could leap a bit farther, get to difficult-to-reach food, and make its escape from predators. Gradually, as natural selection favoured these better-adapted individuals and their descendents, the flying squirrels of today evolved.
Most flying squirrels live in the jungles of Asia, where being able to glide from tree to tree is helpful for finding food and evading predators, which include cats, raccoons and coyotes. The biggest threat they face, however, is destruction of their habitat.
The largest of them is the woolly flying squirrel (Eupetaurus cinereus) found in Pakistan, which can grow up to 60cm in length (minus its tail). The smallest, pygmy flying squirrels, are found in the tropical rainforests of Borneo and Malaysia. They measure less than 10cm long and look like large butterflies flitting through the treetops.
Two species (Glaucomys sabrinus and Glaucomys volans) live in North America, while the Siberian flying squirrel (Pteromys volans) is native to parts of northern Europe. In Helsinki, where the Siberian flying squirrel is protected, there are now 25 nests in the city’s wooded Central Park, compared to just six in 2014.
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