Bats never "get in your


Natural History

General information on insectivorous bats found in North America.



Pennsylvania bats in general

Bats are the only mammals that fly. Their wings are thin membranes of skin stretched from fore to hind legs, and from hind legs to tail. The name of their order, Chiroptera, means "hand-winged." Their long, slender finger bones act as wing struts, stretching the skin taut for flying; closed, they fold the wings alongside the body.

Pennsylvania bats range in size from the hoary bat (length, 5.1-5.9 inches; wingspread, 14.6-16.4 inches; weight, 0.88-1.58 ounces) to the tri-colored bat (length, 2.9-3.5 inches; wingspread, 8.1-10.1 inches; weight, 0.14-0.25 ounces). Eleven species of bats occur in Pennsylvania. Two of these species have been reported only a few times.

All Pennsylvania bats belong to the Family Vespertilionidae, and are also known as evening bats or common bats. They are insect eaters, taking prey on the wing or gleaning them from vegetation. Often they feed over water, and some species occasionally land and seize prey on the ground. A bat can consume more than its body weight in insects in a single night. Back to top

How bats "see" to feed

The eyes of our bats are relatively small, but their ears are large and well developed. Unique adaptations help bats fly and catch prey in total darkness. While in flight, a bat utters a series of high-pitched squeaks (so high, in fact, they are almost always inaudible to humans), which echo off nearby objects-bushes, fences, branches, insects-and bounce back to the bat's ears. Split-second reflexes help the creature change flight direction to dodge obstructions or intercept prey.

A bat can use its mouth to scoop a small insect out of the air. A larger insect is often disabled with a quick bite, cradled in a basket formed by the wings and tail, and carried to the ground or to a perch for eating. If an insect takes last second evasive action, the bat may flick out a wing, nab its prey, and draw the insect back to its mouth. Bats have sharp teeth to chew their food into tiny, easily digested pieces. Back to top

Bats and their pups

Most bats mate in late summer or early fall, although some breed in winter. The male's sperm is stored in the female's reproductive system until spring, when fertilization occurs. The young, born in summer, are naked, blind, and helpless. They are nursed by their mothers (bats are mammals, as are humans, deer, and many other animals), and by six weeks of age, most are self-sufficient and nearly adult size.

The reproductive potential of bats is low. Most bats, including the smaller species, usually bear a single young per year; the larger species may have up to four. There is only one litter per year. Back to top

Summertime behavior

None of Pennsylvania's bats are active during the brighter hours of daylight, preferring to make their feeding flights in late afternoon, evening, and early morning. During the day, they roost-singly, in pairs, in small groups, or in large concentrations, depending on the species. They seek out dark, secluded spots such as caves, hollow trees, and rock crevices. They may also congregate in vacant buildings, barns, church steeples, and attics; some hide among the leaves of trees. They hang upside down, by their feet.

In fall, winter, and early spring, insects are not readily available to bats in Pennsylvania and other northern states. At this time, three species migrate south; the others hibernate under the ground, usually in caves and certain abandoned mines. Back to top

Winter survival

Bats are true hibernators. Throughout the winter, they eat nothing, surviving by slowly burning fat accumulated during the summer. In a hibernating bat, the body temperature drops close to the air temperature; respiration and heartbeat slow; and certain changes occur in the blood. Bats can be roused fairly easily from hibernation, and often are able to fly 10-15 minutes after being handled. Most favor cave zones having the lowest stable temperature above freezing. During winter, bats may awaken and move about within a cave to zones of more optimum temperature. In many caves, bats of several species hibernate together. Back to top

Spooky myths about bats

Perhaps because of their nocturnal natures and secretive habits bats have long been feared. A number of misconceptions exist about them: they are "prone to rabies"; their droppings are a "dangerous source of tuberculosis and other diseases"; they are "aggressive and often attack people"; they are "dirty and ridden with lice."

Current scientific thought is that bats are no more apt to contract rabies than other warm-blooded animals. (People should not handle any wild animal they may come in close contact with.) There is no evidence to suggest that bats-or their droppings, called "guano"-transmit tuberculosis to man. A host of scientific studies indicate that healthy bats do not attack people, and even rabid bats rarely become aggressive. Bats need to keep themselves extremely clean to fly. They host no more parasites than other animals, and parasites that do afflict bats are very specialized and rarely pose problems to humans. Back to top

Threats to bats

Colonial bats may congregate at favorite roosting sites, often in buildings if other natural cover is depleted. While these bats do no real harm to human occupants, their droppings, odor, and noise may become a nuisance. To exclude bats, cover fireplace chimneys with l /4inch hardware cloth, and weatherstrip around outside doors. Entrance holes-cracks in walls, damaged siding, broken windows-should be sealed after the bats leave to feed at night, or, preferably, after they depart in the fall. (Sealing a roost in June or July would trap flightless young inside.) [more on evicting]

Exterminating is a questionable practice. Poisons used on bats can be dangerous to humans, and may cause sickened bats to scatter and fall to the ground, where they are more likely to come into contact with people and pets; therefore, only Certified Pest Control Operators are permitted to use toxic pesticides to control bats. [more on exterminating]

To counterbalance their low reproductive rates, bats are relatively long-lived. Some have been banded, released, and recaptured more than 20 years later. Because they feed in mid-air and are active at dusk and at night, bats are not often caught by predators. Owls and hawks take some, as do housecats, raccoons, and foxes. Rat snakes occasionally eat hibernating bats. Other causes of mortality include cave floods, vandalism, and habitat disturbance.

The greatest threat to bats comes from humans. In winter, hibernating bats may be aroused by people exploring caves; repeated disturbances force bats to burn precious calories needed for overwintering. Caves may be flooded by dams, or dynamited shut. Some scientists suspect that widespread use of pesticides also harms bat populations. Back to top

Dawn return at a bat managed structure in Canoe Creek State Park, Pennsylvania


"Echolocation" is how bats use sounds to visualize objects in total darkness. It's the envy of aerospace engineers worldwide; no machine comes anywhere close to duplicating what these tiny animals take for granted.

A Bat Call

A "bat detector" can give us a representation of what the bats are saying. Play the bat call to hear a few seconds of a bat "searching" as it flies by. At 3/4 through the sample, you will hear a "feeding buzz" as the bat senses and closes in on its prey.


A big brown bat with her pup.


Big browns roosting in barn.


Winter disturbance to many caves is discouraged or even banned by landowners and modern caving organizations.


State threatened small footed bats before a vandalized cave was protected in central PA.

This information is adapted from the Pennsylvania Game Commission's Wildlife Note #175-35. Other Wildlife Notes on other animals are available through PGC, Bureau of Information and Education, Dept. MS, 2001 Elmerton Avenue, Harrisburg, PA 17110-9797