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Big Brown Bat

Eptesicus fuscus

The big brown bat can often be found roosting in home, barns and churches throughout the Chesapeake Bay watershed. (Angell Williams/Flickr)
The big brown bat can often be found roosting in home, barns and churches throughout the Chesapeake Bay watershed. (Angell Williams/Flickr)

The big brown bat is a large copper or chocolate brown bat with long fur, rounded ears and a broad nose.


The big brown bat is a large bat with long, glossy fur that is oily in texture. Its dorsal (back) fur ranges in color from light copper to chocolate brown; its ventral (abdominal) fur is lighter, from pinkish to olive buff. Its naked face, ears, wings and tail membrane are black. The bat has short, rounded ears, a broad nose, fleshy lips, large and bright eyes and sharp, heavy teeth capable of causing severe bites. Adults have an average wingspan of about 13 inches; females are slightly larger than males.


Found in cities, towns, rural areas and deciduous forests. Often hangs upside down to roost during day or to hibernate during winter in homes, barns, silos, churches, tree cavities and caves. Some remain loyal to their chosen over-wintering site for their entire lives.


Found throughout the Chesapeake Bay watershed; range extends from southern Canada through North and Central America to the southern tip of Mexico. They do not migrate.


The big brown bat feeds after sunset on beetles and other flying insects, including moths, flies, flying ants, lacewing flies, dragonflies and crop and forest pests. Adults use echolocation (the echoes of their calls) to locate insect prey in flight. Efficient feeders can fill their stomachs in about an hour; they often rest between meals.


Flying bats are sometimes captured by owls and falcons. Secluded roosts can protect adults from predators. Young are sometimes taken from roosts by snakes, raccoons and cats, particularly if the young have fallen to the ground.


Adults fly strong, straight courses at 20 to 30 feet high.


Adults use echolocation to avoid obstacles and locate insect prey in flight. Adults will squeak and hiss at each other in their roost. Young separated from their mothers squeak continuously to call for help. Loud squeaks can be heard from more than 30 feet away.

Reproduction and Life Cycle:

Adults mate in fall before hibernation. Females give birth to one or two “pups” in late May or early June. Females raise young in “maternity colonies” that range in size from five to several hundred animals. During this time, males roost alone or in small groups. Mothers will transport young from one roost to another, but leave young behind in clusters while hunting for food. Mothers are able to recognize their own young in clusters and will lick pups around their lips and face before nursing. Pups learn to fly within 18 to 35 days and are weaned two weeks later. Pups will continue to join their mother on foraging flights for two to three weeks after learning to fly. Adults can survive up to 19 years in the wild. A number of adults die during their first winter, particularly if individuals have not accumulated enough fat to survive hibernation. Males tend to live longer than females. 

Other Facts:

  • Their Latin name Eptesicus is derived from a Greek word meaning “house flyer.”
  • Big brown bats can reach flying speeds of up to 40 miles per hour.
  • The big brown bat is one of several bat species that have been affected by white-nose syndrome, a fungal disease that has devastated bat populations across eastern North America.

Sources and Additional Information:

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