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.
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.
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.
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.
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.
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.
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.