Free-tailed Bat

Free-tailed Bat

Molossinae
Tomopeatinae

Molossidae, or free-tailed bats, are a family of bats within the order Chiroptera. They are generally quite robust, and consist of many strong flying forms with relatively long and narrow wings. Another common name for some members of this group, and indeed a few species from other families, is mastiff bat. The western mastiff bat, Eumops perotis, a large species from the southwestern United States and Mexico with wings over 0.5 m (1.6 ft) across, is perhaps one of the best known with this name. They are widespread, being found on every continent except Antarctica.

The family name is derived from a length of "free" tail, projecting beyond the end of the uropatagium - the membrane that connects the base of the tail to the hind legs. The tail is usually best seen when resting. A special ring of cartilage slides up or down the tail vertebrae by muscular action to stretch or retract the tail membrane. This gives many species a degree of fine tuning in their flight maneuvers to rival their day-flying ecological equivalents, such as swifts, swallows and martins. As a result, these animals include the fastest flying of all bat species among their number. The dental formula of free-tailed bats varies between species:

Free-tailed bats are usually grey, brown, or black in color, with some exceptions. They range from 4 to 12 cm (1.6 to 4.7 in) in length, excluding the tail, and can weigh from 8 to 220 g (0.28 to 7.8 oz), depending on species. They are insectivorous, and catch their food on the wing. While some species roost in small groups in hollow trees or rocky crevices, some cave-dwelling species form vast colonies of up to 50 million individuals.