Little Brown Bat

Little Brown Bat

Little brown myotis, Little brown bat, Little brown myotis

Myotis lucifugus
Population size
Life Span
6-30 yrs
Top speed
35 km/h
5-14 g
6-10 cm
22-27 cm

The little brown bat or little brown myotis (Myotis lucifugus ) is an endangered species of mouse-eared microbat found in North America. It has a small body size and glossy brown fur. It is similar in appearance to several other mouse-eared bats, including the Indiana bat, northern long-eared bat, and Arizona myotis, to which it is closely related. Despite its name, the little brown bat is not closely related to the big brown bat, which belongs to a different genus.

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Its mating system is polygynandrous, or promiscuous, and females give birth to one offspring annually. The offspring, called pups, are quickly weaned and reach adult size in some dimensions by three weeks old. The little brown bat has a mean lifespan of 6.5 years, though one individual in the wild reached 34 years old. It is nocturnal, foraging for its insect prey at night and roosting in hollow trees or buildings during the day, among less common roost types. It navigates and locates prey with echolocation.

It has few natural predators, but may be killed by raptors such as owls, as well as terrestrial predators such as raccoons. Other sources of mortality include diseases such as rabies and white-nose syndrome. White-nose syndrome has been a significant cause of mortality since 2006, killing over one million little brown bats by 2011. In the Northeastern United States, population loss has been extreme, with surveyed hibernacula (caves used for hibernation) averaging a population loss of 90%.

Humans frequently encounter the little brown bat due to its habit of roosting in buildings. Colonies in buildings are often considered pests because of the production of waste or the concern of rabies transmission. Little brown bats rarely test positive for rabies, however. Some people attempt to attract little brown bats to their property, but not their houses, by installing bat houses.

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Not a migrant


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The Little brown bat has small ears that do not reach the nose when pointing forward. The animal has blunt, medium-high tragus. The hind feet are large, covered with hairs, extending past the toes. Meanwhile, front and hind limbs have 5 metapodials. The glossy fur of the animal generally ranges in color from dark brown, golden brown and reddish to olive brown. However, there have also been known albino individuals among this species. The ventral side of the little brown bat is lighter. The animal has dark brown or black, almost hairless wing and interfemoral membranes. Males are smaller than females, which is most prominent during the winter months.



The Little brown bat is distributed across a vast territory, including Alaska, Canada and the USA, from the Pacific to Atlantic coasts. These bats also inhabit some forested areas of Mexico, found at high elevations. They usually occur in forests, living along lakes and rivers. Little brown bats use buildings, where they gather into nursery colonies. During the winter months, the animals hibernate, usually in caves or mines.

Little Brown Bat habitat map
Little Brown Bat habitat map
Little Brown Bat
Public Domain Dedication (CC0)

Habits and Lifestyle

The Little brown bats are nocturnal. They typically enter torpor by day, appearing from their roosts at dusk. While at roosts, the bats are not territorial, living in large colonies of up to 300,000 individuals in one roost. These animals have two peak periods of activity: one takes place approximately 2 - 3 hours after dusk and the other occurs before down. They generally come back to their roosts at around 4 - 5 o'clock in the morning. During the winter months, they undergo hibernation, which varies in time, depending on location and altitude of a given roost. Usually, they enter hibernation between September and November, coming out between March and May. Meanwhile, young bats enter hibernation quite late, since they need to store fat, which will help them survive during the winter. In addition, pups do not travel long distances to hibernation roosts. The little brown bats travel not more than 100 miles.

Group name
Seasonal behavior

Diet and Nutrition

The Little brown bats are insectivores, they feed upon a wide variety of insects, including hoppers, mosquitoes, midges, caddisflies, moths, small beetles and, occasionally, spiders.

Mating Habits

50-60 days
1 pup
4 weeks

Little brown bats have polygynandrous mating system. They have two phases of mating, during which males mate with a number of females; the active phase, when both mates are awake and alert, and the passive phase, when active males mate with torpid bats of both sexes. They mate between September and October, while ovulation and fertilization takes place in spring. After 50-60 days of gestation, the female yields a single pup. The female is able to distinguish its offspring from other pups due to identifying call and odor. The baby is nursed by its mother, feeding exclusively upon maternal milk for the first 18 - 21 days and being weaned at the age of 3 weeks. Then, at about 4 weeks old, the pup begins to fly, becoming independent. Female bats first give birth within the first or second year of their lives.


Population threats

Little brown bats are threatened with loss and fragmentation of their natural habitat as a result of deforestation. Presently, the animals suffer from a fungal disease known as “white-nose syndrome". Cold and humid environment of their hibernaculas provides ideal conditions for fungus growth, which occasionally invades the bodies of hibernating bats, leading to debilitation and high numbers (up to 90%) of mortality. The animals are also exposed to human disturbance. Other notable concerns include use of pesticides and use of cyanide in mining.

Population number

The Little brown bat is widespread across its range, but the overall number of their population is currently unknown. On the IUCN Red List, the Little brown bat is classified as Least Concern (LC) with a stable population trend.

Ecological niche

Little brown bats play a significant role in the local ecosystem, controlling populations of insects. Moreover, they hugely contribute to pollinization and serve as seed dispersers of a wide variety of plant species.

Fun Facts for Kids

  • During the winter, the animals undergo hibernation, enduring up to 50 degree Celsius change in temperature without any negative consequences.
  • Little brown bats have three types of roosting sites: day roosts, which are typically located in caves, trees or under rocks; night roosts, found in the same places as day roosts, though separate in order to keep the feces in different places and thus protect the animals from predators; and finally, nursery roosts, which are larger than day roosts, occurring in large hollows or buildings.
  • These bats are night hunters, eating a huge number of insects. An average bat will consume as many as 1000 insects, while a pregnant female will eat up to her whole body weight per sitting.
  • In order to save energy, these animals sleep 20 hours a day on average.
  • During the summer months, females rear the pups, living separately from males. By the approaching of winter, they reunite to mate and hibernate together. Because of food shortage, they usually leave their roosts, looking for larger hibernaculas.
  • When cruising, these animals give out up to 20 calls per second in order to locate prey and objects.


1. Little Brown Bat Wikipedia article -
2. Little Brown Bat on The IUCN Red List site -

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