Evening bats, Nycticeius humeralis, are the only members of the genus known as Nycticeius. They greatly resemble the brown bat but are much smaller. They are a bronze brown color with lighter shades on their underside. From tip to tail, these bats only reach a size of 4 inches with a wingspan of 10 to 11 inches.
Their geographic range includes the Midwest of the United States and spans east. They will live as far south as northeastern Mexico and Florida and as far north as Pennsylvania. These bats live in colonies and the populations in their northern range will migrate south to warmer weather. Even after migrating, they will go into states of torpor during times of cold weather. They are insectivores that make their homes in trees, leaf litter, Spanish moss, and even in man-made buildings.
Like many species of bats, they mate in the fall, migrate for the winter, and their eggs become fertilized in the spring, usually around March or April. They practice delayed fertilization so that the females can wait to become pregnant at a time where there are steady food sources. The females will roost in maternity colonies while they are raising their young. Their young are born in the late spring or early summer.