The Great Lakes region is home to many species of bats. Among the most common is the little brown bat (Myotis lucifigus), with a range covering most of the continent and extending as far north as any bat in North America.

The little brown bat is a small mammal, measuring 80-95mm (3.1-3.7 inches) from head to tail and weighing 6-12 grams (0.2-0.4 ounces). Its coat is an olive-brown to dark-yellowish brown on the back and paler underneath. The generic name Myotis, which means “mouse ear” in Latin, presumably comes from its mouse-like ears which measure 13-16mm (0.5-0.6 inches).

Little brown bats use echolocation to find and capture prey. They emit pulses of high frequency sound (20-130 kHz) that bounce off nearby objects. The bats then use the echoes to determine the object's distance, size, and shape. They feed primarily on aquatic insects, including mayflies, caddis flies, and stoneflies. They will also feed on other flies, wasps, moths, and beetles to supplement their diet. Typical summer foraging areas include forest edges, along streams and lakes, and sometimes in small cultivated fields. Young little brown bats can eat up to 1.8 grams of insects/night; lactating females can eat up to 3.7 grams of insects/hour due to increased energy demands.

Little brown bat habitat and behavior vary seasonally. Males and females typically spend the summers apart from one another. They come together again in early fall when courtship and mating are initiated. After mating, they’ll over-winter in moderately sheltered hibernacula, including caves, mine tunnels, and occasionally in hollow trees. Upon leaving their hibernacula in spring, females will form small groups and move to summer roosts where they bear and nurse their young. These nursing sites are typically used year after year. Young are typically born from early June through early July, and are usually capable of flight within 21 days. Little is known about the summer whereabouts of males, though they appear in common places such as caves, forests, and occasionally attics.

While considered a warm-blooded mammal, the little brown bat has the ability to withstand drastic changes in body temperature. This probably explains why summer nursery colonies can survive in areas where night temperatures reach near freezing and day temperatures are very hot. During times of rest, little brown bats enter a physiological state called torpor. As with hibernation, torpid bats experience reduced heartbeat, respiration, and body heat. Torpid bats can “awaken” within a relatively short time to feed, drink, or even switch positions on the roost.

While predation is not a problem for little brown bats, hundreds are killed each year by exterminators for taking roost in homes or other human dwellings. This is unnecessary, as sealing the point of entry after bats have left for the night is much cheaper, safe, and effective. The next time you look towards the sky at dusk, keep your eyes open – you may just catch a glimpse of a little brown bat!