Bat, only mammal that can fly. Bats have modified hands and arms that serve as wings capable of sustained flight. They have been flitting across the night skies since the Eocene Epoch, some 50 million years ago. In all this time, the physical features of these animals have changed very little. Fossil specimens from Europe and North America are nearly indistinguishable from living forms.

There are nearly 1000 living bat species, accounting for almost a quarter of all mammal species. These species are divided among two major groups. The Megachiroptera, or megabats, are large animals, commonly known as Old World fruit bats. They are mainly fruit-eaters and are found only in tropical habitats of Africa, India, and Australasia. The Microchiroptera, or microbats, are smaller, eat a variety of foods from small mammals to fish, and are much more widely distributed.

Nearly all bats are nocturnal (active at night) or crepuscular (active during the twilight of dawn and dusk). To get around in the dark, many nocturnal bats rely on a sophisticated form of sonar known as echolocation for navigating and finding prey. Many bats, especially the crepuscular ones, have exceptionally good eyesight designed for low levels of light. Only those bats that live on remote islands lacking birds of prey routinely fly during the day.

Throughout history, people have associated bats with other, more frightful creatures of the night. As such, bats have endured centuries of unjustified abuse. While most medieval superstitions about bats have perished, some misconceptions surrounding these animals persist today. Bats continue to appear as villains in motion pictures and children's cartoons. Despite studies that give evidence to the contrary, they are still frequently miscast as carriers of disease, such as rabies. On average, only one person per year dies from rabid bat bites in the United States, far fewer than die from dog bites or bee stings.

In recent decades, people have begun to appreciate bats for their beneficial roles. Bats are the most important natural enemies of night-flying insect pests. Bats are important pollinators of plants, pollinating at least 500 species, including bananas, mangoes, cashews, dates, figs, and agave, from which tequila is produced. Without these helpful night fliers, many bat-pollinated plants-and the many animals that depend on them for food and shelter-would disappear from the earth. Bats also produce a nitrogen-rich fertilizer known as guano.

* Contributed By: David George Gordon, B.S. Natural history and science writer. Author of The Eat-a-Bug Cookbook and The Compleat Cockroach: A Comprehensive Guide to the Most Despised (and Least Understood) Creature on Earth.

"Bat," Microsoft® Encarta® Online Encyclopedia 2001 http://encarta.msn.com © 1997-2001 Microsoft Corporation. All rights reserved.