The evening bat is a species of bat in the vesper bat family, Vespertilionidae, that is native to North America. It is a small bat (7–15 grams) found throughout much of the midwestern and eastern United States as well as northeastern Mexico. In many areas (especially the Gulf Coast states) they are very common, but they may be declining in some states. During the summer, they commonly roost in tree cavities but are also found occasionally in man-made structures. Colonies are generally small in trees, but groups can reach nearly 1,000 individuals, especially in buildings. Evening bats feed heavily on beetles (Coleoptera), but they also eat moths (Lepidoptera) and to a lesser extent flies (Diptera) and other insects.
The reproductive pattern of this species is virtually unknown, but in other temperate zone Vespertilionid species, breeding occurs in fall and sperm is stored in the female reproductive tract until spring when ovulation and fertilization occurs. Two young are born in June and are capable of foraging on their own three weeks after birth.
The evening bat is generally thought to be migratory, but recent work suggests that some individuals may be non-migratory, even near the northern edge of their range. During winter, individuals continue to roost in tree cavities or buildings, and they may forage on warm days.