No copies of this work may be distributed electronically outside of the subscribed institution, in whole or in part, without written permission from the JHU Press . Rhinopterus sometimes has been treated as a distinct genus. Weights in the species E. fuscus range from 14 to 30 grams and in E. serotinus and E. nilssoni from 8 to 18 grams. The usual color is dark brown to black above and paler below. A buffy wash is often present.
Some African species have white or translucent membranes.
In the subgenus Rhinopterus the upper parts are pale fawn, the underparts are buffy, and the arms, legs, and tail are covered with small, horny, raised areas, giving a scabby appearance. Colonies of E. fuscus are often found in attics and church belfries and behind shutters and loose boards of buildings. Hibernating sites include houses, tunnels, and storm sewers. Big brown bats usually emerge about sunset, with slow, ponderous, fluttering flight, and generally feed near the ground at lower levels than those of bats with a rapid, erratic flight. E. fuscus reportedly does not make substantial migrations or move very far from its place of birth.