Natural Histories

photograph of a Sunda Pangolin

Little Brown Bat

Myotis lucifugus


Little brown bats weigh between 5 and 14 g, the females tend to be larger than males. The glossy fur of this species can be dark brown, golden brown, reddish to olive brown. The ventral side typically has lighter colored fur and the wings and interfemoral membranes are dark brown or black with almost no existing fur. The ears of little brown bats do not extend past the nose when laid forward (relatively small). The hind legs have large feet with hair extending past the toes.


The little brown bat can be found in southern Alaska, Canada, throughout the United States and also the higher elevation forests of Mexico. This species is not found in Florida, the southern Great Plains of the U.S., southern California, and parts of Virginia and the Carolinas. Little brown bats prefer forests near water but some subspecies prefer dry climates (where water is provided by condensation on cave walls or fur).

Feeding Behavior and Diet

This species is an insectivorous bat (consuming only insects) favoring aquatic insects. Little brown bats are opportunistic feeders catching prey mid-flight by taking swooping or dipping maneuvers while feeding on swarms of insects so they do not have to search for more food.  Lactating females consume larger insects because they have a higher food demand (consuming 110% of their body weight in insects).


These bats mate in two phases just before hibernation; active and passive. During the active phase, both females and males are awake and alert. During passive phase, active males mate with torpid (sleeping/sub-hibernation state) individuals of both sexes (35% being homosexual). Passive phase of mating is random and promiscuous, females mating with more than one male. Males mate with more than one female during both active and passive phases. After mating, females delay ovulation and store sperm for 7 months until spring. In June – July females give birth to one pup (bat young) per year, 50-60 days after fertilization (female no longer delays ovulation to allow fertilization). Young are nursed by lactating females until pups begin to fly at 4 weeks old.  Male little brown bats do not reach sexual maturity until they reach the end of their first year.

Months and Times of Activity

This bat species is primarily nocturnal, emerging from roosts at dusk with the highest time of activity being a few hours after dusk. Before dawn they return to their roosts to enter daily torpor (lowering metabolic and heart rates to conserve energy). Little brown bats roost in three different locations depending on the time of day and year. During active times (day and night), these bats roost in buildings, trees, under rocks, and piles of wood. Day roosts have very little or no light; provide good shelter and a steady ambient temperature. Night roosts are confined spaces with a steady ambient temperature below 15 degrees Celsius, many bats roost close together, increasing the overall temperature. Night and Day roosts are in separate locations and are occupied during spring, summer and fall.  Hibernation roosts include abandoned mines or caves with temperatures always above freezing and high; northern populations hibernate from early September until mid- May while southern populations hibernate from November until mid-March. These roosts can sometimes be shared by other bat species. There are also nursery roosts are occupied by females and their offspring, where it is warmer than ambient temperature.

Special Features, Stories, Relationships

•    These bats use high frequency chirps for echolocation, a method of using sound to locate prey and surrounding objects.

•    Little brown bat populations are threatened by “white-nose syndrome” a fungal disease that grows quickly in cold, damp environments such as bat hibernation sites. This disease causes the bat to arouse from hibernation more frequently than normal to increase immune responses, causing higher metabolic demands. The excess energy expense causes bats not to survive hibernation because there is no longer enough stored energy.

•    To read myths featuring this animal go to;

•    Children’s book featuring this animal: Boo, the Little Brown Bat by Paula Pifer


Havens, A. 2006. "Myotis lucifugus" (On-line), Animal Diversity Web. Accessed November 04, 2014 at