Maryland is home to 10 species of bats which can be divided into two groups: cave bats and tree bats (see Table 1 below). Cave bats are those species that hibernate in caves, tunnels, or man-made structures such as homes, while tree bats either migrate or overwinter under tree bark, in tree cavities, or in leaf litter.

While big brown bats are the species most likely to colonize homes, evening bats and all cave bat species are known to enter buildings, including the federally endangered Indiana bat, the federally endangered northern long-eared bat, and the state endangered eastern small-footed bat. Evening bats and cave bats are most likely to colonize homes from March 1 through August 31; additionally, big brown bats may overwinter in homes from September 1 to February 28.

For more information see the Maryland Department of Natural Resources' Guide to Maryland Bats.