Only one mammal is capable of true flight: the bat, of which an estimated 1,200 species exist around the world. Other mammals that may come to mind -- flying squirrels, for instance -- don't actually fly; they glide. Bats, on the other hand, are alone in the mammal class in their ability to flap wings to create thrust for upward motion and sustained flight.
Bats devour pest insects in large quantities and are essential to the pollination of many plants around the globe. A small bat eats about 1,000 mosquitoes or similar-size insects in an hour; a pregnant or lactating bat eats her own body weight in bugs for dinner. A diverse mammalian order (Chiroptera), bats have a considerable size range: Tiny bumblebee bats weigh less than a penny, while flying fox bats have wingspans up to 6 feet.
Some species aren't actually "blind as a bat"; some see well and the rest can see, though some only poorly. No matter how well any given species sees, though, they all fly and hunt exceptionally well, even in the pitch black, and without getting tangled in your hair as movie cliches portray. Bats emit high-frequency vocalizations and determine the size, location and other characteristics of objects by the way their sounds echo back. This sonar system, echolocation, allows bats to navigate in flight and locate prey. With it they can detect something in their vicinity as fine as a single strand of hair.
Bats spend most of the day literally hanging out in their roost and sleeping, taking flight around dusk and feeding throughout the night. Many bat species use their flight capabilities to migrate. Some species go for the long haul, traveling south from Canada to the Gulf Coast region for the winter. Numerous species fly to suitable hibernation locations within 300 miles of their home.
Mammalian gliding may be confused with flight, but it isn't the same. Technically, gliding is defined as downward motion through the air at an angle of less than 45 degrees. Gliding mammals, which rely primarily on skin flaps to ride the air, cannot create upward momentum. Flying squirrels are perhaps the best-known gliding mammals, but there are others, such as gliding possums. The colugos, otherwise known as flying lemurs, of Southeast Asia are a less familiar example of gliding mammals. Also, numerous gliding reptiles exist, including various types of lizards and frogs. These animals glide with thin flaps of skin attached to the legs or between the toes.