Nature Note: the Big Brown Bat
By Chris Carpenter

That’s right, it’s big, it’s brown and it’s a bat. Well you don’t have to hang around biologists too long to see that many times an animal’s name is simply very descriptive. Actually the Big Brown Bat has another name, Eptesicus fuscus. This Latin name refers to the animal’s habits and color, Eptesicus means “house flyer” and fuscus means “dusky.”

The Big Brown Bat is Kentucky’s second largest bat with a wingspan of 12-15 inches. Their body length is 3-5 inches and they weigh 0.5-0.7 ounces or about the same as your car key. Big Browns have silky, long, golden brown fur on their backs with lighter undersides. They have black wings and ears and a dark muzzle.

Big Brown Bats have been known to live as long as 19 years, and unfortunately their biggest threat is humans. Natural predators include American Kestrels, owls, weasels, rat snakes and bullfrogs.

In Kentucky it is found nearly statewide, and it is very closely associated with humans and their buildings often roosting in barns, attics and churches. Have no fear if these bats inhabit a building on your property; they are only looking for a place to spend the day.

The Big Brown Bat is one of the first species to emerge from hibernation and also one of the first bats to leave its roost and begin foraging for insects each night. They can be recognized by their large size and relatively slow wing beats.

When they emerge at dusk they will promptly begin the insect extermination that makes these animals so beneficial to humans. They eat beetles, mosquitoes, flies and ants in large quantities. Big Browns can consume their own body weight in insects in just one night. In the winter Big Brown Bats will move into mines and caves to hibernate.

Mating occurs in autumn, and they usually have twins born in May and June that are hairless and helpless with their eyes closed. The pups nurse for three to four weeks and can fly one month after birth!

Check them out this spring and summer and be glad if you have your own insect-eating colony of Big Brown Bats.

Chris Carpenter is a biologist with Kentucky’s Touchstone Energy Cooperatives