M. sodalis concentrates in caves during the fall, preliminary to winter hibernation, but disperses to other habitats for the summer. The diet of Myotis usually consists predominantly of insects. M. vivesi, however, catches fish and small aquatic crustaceans. The exact way in which this is accomplished is unknown, but the long feet and enlarged hind claws presumably aid in the capture. Several other species, including M. hasseltii and M. macrotarsus, may also catch fish.
Most species are gregarious to some extent.
Usually the females of Myotis form maternity colonies to bear young, with few or no males present until after the young are born. Colonies of several other species are in the same size range, but those of M. austroriparius usually number many thousands, a range of 2,000-90,000 having been reported in Florida. These great aggregations disperse in October. In the summer the females collect in smaller groups at other caves to bear young, while the males assemble at sites nearby. After late July the males move into the maternity colonies.