Big Brown Bat

(Eptesicus fuscus)​

Big brown bat in a cave by John MacGregor
Big brown bat by John MacGregor

Description:  One of Kentucky’s largest bats, the big brown sometimes attains a length of nearly 5 inches and can have a wingspan of more than 13 inches. These bats are glossy brown in color, slightly lighter underneath. Key features include a large, hairless muzzle, a blunt-tipped tragus, and a keeled calcar.

Range:  Occurs throughout most of North America from central Canada, south through Central America into northern South America.

Distribution in Kentucky:  See Map

Kentucky Occurrence Summary:  The species is a year-round resident in Kentucky, in all likelihood not moving great distances between winter and summer roost sites. Big brown bats occur statewide, although they appear to be absent from the Mississippi Alluvial Plain in the far western part of the state.

Habitat and Life History:Big brown bats are associated primarily with man-made structures, as they have adapted well to the changes humans have brought to the landscape. Consequently, they are the bats most often encountered by humans. All known Kentucky maternity sites have been found in buildings of some type or under bridges. These hardy bats also roost in the eaves of buildings during winter unless the temperatures become too extreme. The species forages in a great variety of open and semi-open habitats, often around streetlights. These bats have relatively large teeth, which aid them in consuming their preferred prey…beetles. They have been called a ‘friend of farmers’ due to the fact they eat several agricultural pests such as the cucumber beetle whose larva can greatly affect corn production. Maternity colonies consist of a few to more than one hundred females. Each female generally gives birth to twins in early June. Males are primarily solitary. In winter, big brown bats hibernate in caves, usually in the coldest sections near the entrance. They typically roost singly or in small groups of less than a half-dozen individuals, often in rock crevices.

Threats:  Big brown bats are susceptible to white-nose syndrome, a devastating disease that has caused unprecedented mortality in some of our hibernating bat species, especially in the northeastern U.S.

Big brown bat showing teeth used to eat beetles Big brown bat showing teeth used to eat beetles
Photo by John MacGregor
Big brown bats under bridge in gap between concrete beams Big brown bats under bridge in gap between concrete beams
Photo by John MacGregor
Evening bat (top) and big brown bat (bottom) Evening bat (top) and big brown bat (bottom)
Photo by James Kiser