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The metacarpal bone and the second and fifth toe of the forelimbs are elongated, and between these toes is a membrane, called "chiropatagium". The membrane extends from the toes to the body side and from there to the base of the hindlimbs. The entire wing of a bat is called patagium. Many species also have a membrane between the hindlimbs enclosing the tails. This membrane is the uropatagium.
The patagium is full of fine blood vessels, muscle fibres and nerves. When it's cold, the bats wrap themselves up in their wings like in a coat. In warm weather they stir their wings in order to cool their bodies.
The thumb and sometimes the second toe of the forelimbs have claws, as do all five toes of the hindlimbs. The rear claws allow bats to hang on branches or ledges. Bats are also able to move on the ground, but they are rather clumsy.
All bats are active at night or at twilight, so the eyes of most species are poorly developed. Their senses of smell and hearing, however, are excellent. By emitting high-pitched sounds and listening to the echoes, the microbats locate prey and other nearby objects. This is the process of echolocation, a skill they share with dolphins and whales.
The teeth resemble those of the insectivores. They are very sharp in order to bite through the chitin armour of insects or the skin of fruits.
A newborn bat can cling to the fur of the mother and be transported, although they soon grow too large for this. It would be difficult for an adult bat to carry more than one young, so normally only one young is born. Bats will often form nursery roost s, with many females giving birth in the same area, be it a cave, a tree hole, or a cavity in a building. Two mammary glands are situated between the chest and the shoulders. Only the mother cares for the young, and there is no continuous partnership.
The ability to fly is congenital, but after birth the wings are too small to fly. Young microbats become independent at the age of 6 to 8 weeks, megabats not until they are four months old. At the age of two years bats are sexually mature.
Small bats are sometimes preyed upon by owls and falcons. Generally there are few animals able to hunt a bat. In Asia there is a bird, the bat hawk , which specializes in hunting bats. The domestic cat is a regular predator in urban areas; they may catch bats as they enter or leave a roost, or on the ground. Bats will land on the ground for feeding, in bad weather, or due to accidents while learning to fly.
The worst enemies are parasites. The membranes with all their blood vessels are ideal food sources for fleas, ticks and mites. Some groups of insects suck exclusively bat blood, e.g. the bat fly . In their caves the bats are hanging close together, so it is easy for the parasites to infest new hosts.
The following advice is only relevant to areas with endemic rabies.
Of the very few cases of rabies reported in the United States every year, most are caused by bat bites. Although most bats do not have rabies, those that do may be clumsy, disoriented, and unable to fly, which makes it more likely that they will come into contact with humans. Although one should not have an unreasoning fear of bats, one should avoid handling them or having them in one's living space, as with any wild animal. If a bat is found in living quarters near a child, mentally handicapped person, intoxicated person, sleeping person, or pet, the person or pet should receive immediate medical attention for rabies. Bats have very small teeth and can bite a sleeping person without necessarily being felt.
If a bat is found in a house and the possibility of exposure cannot be ruled out, the bat should be sequestered and an animal control officer called immediately, so that the bat can be analyzed. This also applies if the bat is found dead. If it is certain that nobody has been exposed to the bat, it should be removed from the house. The best way to do this is to close all the doors and windows to the room except one to the outside. The bat should soon leave.
Due to the risk of rabies and also due to health problems related to their guano, bats should be excluded from inhabited parts of houses. For full detailed information on all aspects of bat management, including how to capture a bat, what to do in case of exposure, and how to bat-proof a house humanely, see the Centers for Disease Control's website on bats and rabies.
Where rabies is not endemic, as throughout most of western Europe, small bats can be considered as harmless. Larger bats can give a nasty bite. Treat them with the respect due to any wild animal.
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