Little brown bat

Myotis lucifugus




Myotis lucifugus (Le Conte, 1831), near Riceboro, Georgia, United States. Six subspecies.


English: Little brown myotis; French: Petite Chauve-souris brune; German: Kleine braune Fledermaus; Spanish: Murcielago marrón Americano.


Wingspan varies from 7.9 to 10.6 in (20-27 cm), and forearms about 1.4-1.6 in (3.5-4 cm). With a body length of 3.1-3.7 in (8-9.5 cm), they are smaller than the big brown bat (Eptesicus fuscus), with which they are often confused. Adults weigh 0.21-0.49 oz (6-14 g), tending toward the higher end before entering hibernation and the lower end when awakening in the spring. A small bat that ranges in color from light to dark brown dorsally and light tan to whitish on its belly. They are similar in appearance to the Indiana bat (M. sodalis), but the little brown bat lacks the keel present on the calcar of the Indiana bat. The dental formula of the little brown bat is (I2/2 C1/1 P3/3 M3/3) X 2 = 38.


Found through much of North America, including southern and south-central Alaska, the southern two thirds of Canada, all but the extreme southeastern, south-central and southwestern United States, and north-central Mexico.


Little brown bats are found in a wide variety of habitats. They spend much of their summer in the hollows of trees, or in attics, barns, between wooden vents, and in other human-built structures. They are typically found near water and/or woods. During the winter, they hibernate in caves.


Males are typically solitary during the summer. Females, however, will form maternity colonies with a dozen to more than 1,000 bats roosting together often in hot locations, such as attics, where temperatures can top 100°F (38°C). During the winter, males and females roost together in caves, sometimes migrating more than 150 mi (250 km) between their winter and summer roosts. A single hibernaculum draws bats from a wide area, often totaling 200,000 bats or more.


These are insectivorous bats that hunt in flight for their favorite prey items—moths, mayflies, and chironomid flies—by either snatching the insect with their jaws or scooping them into their wings and bringing them to their mouths. Adults may eat close to, and sometimes more than, their body weight in insects in a single night. Little brown bats are most active and do the bulk of their feeding early in the evening and at dawn.

H Myotis lucifugus H Myotis daubentonii

Predators may include raptors that catch a bat in flight, or raccoons that reach a roost. However, predation on little brown bats is not prevalent.


A promiscuous species, mating commonly occurs in late summer and early fall as bats begin to move into the hibernaculum. Fertilization is delayed until the following spring. Gestation lasts 50 to 60 days, and the young are born in late spring to mid-summer. Litter size is typically one altricial young per female. After clinging to the mother for a day or two, the young bat hangs in the roost until it reaches about three to four weeks old, when it begins to fly and is weaned. The young reach full size at about two months old, and attain sexual maturity at one to two years. A long-lived bat, individuals in the wild have reached 33 years of age.


Not listed by the IUCN, however, some populations are experiencing declines. Numbers of the subspecies M. l. occultus, for instance, have dropped precipitously, particularly through habitat destruction.


These voracious insectivores help control pest insect populations, and also serve as bio-indicators. ♦

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