Bats are the only mammals that can fly. Chiroptera comes from the Greek roots cheiro (hand) and ptera (wing), named for the similarity of a bat wing to a hand. Bat wings are long arms, hands and extra-long finger bones that are covered with a double layer of thin skin called a membrane. The membrane is thin enough that light can shine through it. The membrane contains blood vessels, nerves, and muscles. In some bats, a membrane extends between the legs and encloses the tail. Some bats have tails that extend past the membrane and others have no tails. In most bats, the thumbs are free from the membrane. These thumbs have claws and are often used for climbing up trees or other structures.
Bat membranes are tough and flexible, allowing bats to move their wings much like people move their fingers. Changing the shape of their wings allows bats to turn and maneuver quickly. Some bats can hover in the air while others glide. When it is cold, the bats fold their wings around themselves. When it is warm, bats flap their wings to cool themselves.
Bats range widely in size, yet the majority of bats weigh less than 1 ounce (25 grams). The largest bat is the Malayan flying fox, which can have a wingspan of 6 feet (1.8 meters) and weigh 3.3 pounds (1.5 kilograms). The smallest bats are the Kitti's hog-nosed bats, also called «bumblebee bats», of Thailand, with a wingspan of 6 inches (15 centimeters) and a weight of about 0.07 ounces (2 grams), less than a penny.
Like other mammals, bats are warm-blooded and fur covers their body. Megachiroptera are characterized by large eyes, small ears, and dog-like snouts. Most Microchiroptera species are characterized by wide, extended ears and odd shaped noses. Bats have weak legs and do not walk long distances. Their feet are small with sharp claws on each toe. Bats use their claws to hold the weight of their body when they hang upside down, which is their normal resting position.
Bats live on every continent on Earth except Antarctica and some remote islands. Most bats live in the tropics and species are most numerous around the equator.
While the most famous bats are the vampire bats, known for eating blood, the majority of bats eat only insects.
Microchiroptera are generally carnivores, meat-eaters, that feed on insects, such as moths, flying beetles, and mosquitoes. Bats can capture insects while flying by catching them in their mouths or scooping them into their tails or wing membranes. Some bats pick the insects off leaves or the ground. One gray bat may eat up to 3,000 insects in one night.Some bats feed on larger prey, animals hunted or caught for food, such as fish, frogs, birds, mice and other bats. A fisheating bat will swoop down and grab fish with its claws. A bat that eats mice will swoop down, wrap the prey in its wings, bite it and then whisk it away to eat it.
The three species of vampire bats are the only bats that feed on blood, sucking up the blood of cattle, sheep, or other relatively large animals. The bats use their razor-sharp teeth to pierce the animal's skin, often while the animal is sleeping. The bats then lap up about 2 tablespoons (30 milliliters) for their meal.
Most megachiropteran species are herbivores, plant-eaters, eating fruit, seeds, leaves, nectar, and pollen.
Bats as a group are crepuscular, meaning they are active at dawn and dusk, or nocturnal, meaning they are active at night. When they are roosting, bats generally hang upside down by their claws. This allows them to simply let go of whatever they are hanging onto and start flying.
With their large ears and small eyes, microchiropteran bats depend upon a complex sound technique called echolocation to help them find prey and move. While flying, these bats send out high-frequency sounds that bounce off of other objects. The bat listens for the bounced sound, and then determines the location, size, distance, and speed of the object—all within a split second. In most bats, the echolocation is at such a high pitch that it is beyond the human hearing range, though humans can hear the sounds of some bats. Researchers are still working to understand exactly how echolocation works. Megachiroptera generally depend upon their eyes to navigate, but some of these bats also use echolocation.
Like all mammals, bats are warm-blooded, meaning they maintain their body temperature. Bats roost in warm places during the cool months to conserve the energy it takes to keep warm. Unlike other mammals, bats can allow their body temperature to drop to the ambient temperature, or surrounding temperature, when they are not active. As their temperature drops, metabolism slows down. During the winter, some bats will drop their body temperatures for months at a time and go into hibernation, meaning they go into a resting state in a safe place, typically without eating or passing wastes. A bat's body temperature can drop to as low as 35.6°F (2°C). These bats survive the winter by living off their storages of fat and making occasional food trips during warmer weather.
Other bat species follow an annual migration pattern, traveling to warmer climates in the cool months and cooler climates in the warm months.
Bats are generally social animals and gather together in roosts. Bats can roost in colonies of several hundred to tens of millions. The number of bats in a roost depends upon the type of bat.
Like all mammals, female bats give birth to live young and feed their newborns milk. Females often roost in large colonies, with many females giving birth in the same area. Bats usually give birth to only one young per year. During their first weeks of life newborn bats cling to their mothers while in flight. Only the mother cares for the young, and there is no lasting relationship between the mother and father.
Bats grow quickly; the young are often flying at four weeks. Young microchiropterans become independent at approximately six to eight weeks, megachiropterans at about four months old. At the age of two years bats are sexually mature.
Bats live about twenty-five years, far longer than most mammals of a comparable size.