The little brown Myotis' fur ranges from brown to yellowish to gray-brown. In its western range, the little brown Myotis prefers mountainous habitat and riparian areas in a variety of forest types. It can often be found roosting in man-made structures such as buildings, attics, and bat boxes in towns and open, arid areas. Little brown Myotis will also roost beneath the bark of dead trees, inside tree cavities, under rocks, and in woodpiles. The little brown Myotis consumes a wide variety of aquatic insects, from midges and mayflies to moths and beetles. Lactating females may consume up to half their body weight in insects during a single night while nursing pups. During winter, the little brown Myotis hibernates in caves and abandoned mines, aggregating in colonies that often number tens of thousands of individuals. This species is particularly susceptible to the fungal pathogen white-nose syndrome, which has caused populations to decline drastically.