Some members of this family are solitary, others roost in pairs or in small groups, and still others generally shelter in colonies. The colonial forms usually return to the same roosting site year after year. Some species remain in colonies throughout the year, whereas others congregate only in winter. A number of forms migrate between summer and winter quarters. Homing ability has been demonstrated in several forms.
Vespertilionids send out ultrasonic sounds through their mouths.
Nearly all members of this family feed mainly on insects. Myotis vivesi is definitely known to feed on fish, and two other species of Myotis are suspected to do so. Antrozous pallidus in captivity has captured and eaten lizards. Vespertilionids generally capture insects in flight, often using the well-developed tail membrane as a pouch in which to manipulate the larger kinds of prey. A fairly definite feeding territory is often established.