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little brown bat

little brown bat (Myotis lucifugus)
Photo © Michael Durham

Features and Behaviors

The little brown bat has shiny, brown fur with black at the roots. The wings and ears are dark brown. The belly fur is lighter than that on the back. Each wing is attached along the side of the foot. This small bat has medium-sized ears, each with a round tragus.

The little brown bat may be found statewide in Illinois. In winter, it lives in a deep cave or mine where the temperature remains above freezing. An attic, steeple or building near a wooded area is the preferred habitat in the summer. The little brown bat is an insectivore, eating mostly moths, caddisflies, leafhoppers, planthoppers and beetle larvae. It can catch a large number of insects in a short time and is able to digest the food within an hour. These bats form colonies when hibernating, and they hibernate in several Illinois locations. Winter colonies include males, females and young. Wintering little brown bats awaken every two or three weeks to excrete wastes. Mating occurs in the fall, winter or spring. Females that mate in fall and winter store the sperm in the uterus until spring, when it is used to fertilize the egg. Females move to their summer quarters in April. Here they will establish maternity colonies. Males move into separate colonies in May or June. The gestation period is between 50 and 60 days. Young are born from May through early July. Usually only one young is born per female. During the first week after birth, the female takes the young bat with her while flying. After that time she leaves it in the maternity colony when she searches for food. A young bat can fly at the age of about one month. When the young bats leave the maternity colony, the adults usually go, too, spreading through several habitats until entering the winter colony. The little brown bat is known to live about 11 years and may live longer.

Illinois Range


​Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Chiroptera
Family: Vespertilionidae

Illinois Status: common, native