Molossidae is one of the twenty families of bats in the mammalian order Chiroptera and part of the microbat suborder. Members of this family are called a molossid, or a free-tailed bat. They are named for their tail, which extends past the uropatagium, a membrane that connects the legs of bats.[1] They are found in all continents besides Antarctica, primarily in caves, forests, savannas, and shrublands, though some species can also be found in deserts, rocky areas, or coastal areas. They range in size from the blunt-eared bat, at 3 cm (1 in) plus a 2 cm (1 in) tail, to the hairless bat, at 18 cm (7 in) plus a 8 cm (3 in) tail. Like all bats, molossids are capable of true and sustained flight, and have wing lengths ranging from 2 cm (1 in) for many species to 9 cm (4 in) in the hairless bat, big bonneted bat, and western mastiff bat. They are all insectivorous and eat a variety of insects and spiders.[1] Almost no molossids have population estimates, though the Mexican free-tailed bat is estimated to have a population of nearly 100 million, as one of the most numerous mammals in the world,[2] while seven species—the blunt-eared bat, equatorial dog-faced bat, Fijian mastiff bat, La Touche's free-tailed bat, Natal free-tailed bat, São Tomé free-tailed bat, and Solomons mastiff bat—are categorized as endangered species, with populations as low as 200.
The 120 extant species of Molossidae are divided between two subfamilies, Molossinae and Tomopeatinae. Molossinae contains 119 species grouped into 18 genera, while Tomopeatinae contains only a single species. A few extinct prehistoric molossid species have been discovered, though due to ongoing research and discoveries the exact number and categorization is not fixed.[3]