The Little Brown Bat is 4 to 5 centimeters long, with a wingspan of 22 to 27 centimeters. They resemble northern long-eared bats and are colonial animals, often living together in large groups. They feed on insects at night using echolocation, a sonar-like system that helps them detect prey. Most active in the hours after sunset, they hibernate from October or November through March or April. This species is threatened by a disease called white-nose syndrome, caused by a fungus.