Molossids (mol-LOSS-ids; members of the family Molossidae) range widely in size from small to moderately large bats. They have a forearm length of approximately 1.1 to 3.4 inches (2.7 to 8.5 centimeters), and weigh from 0.2 to 3.8 ounces (5 to 167 grams). Free-tailed bats are named for their thick tail that extends far beyond the tail membrane (thin layer of skin). The mastiff bats are named after their facial resemblance to the mastiff dog.

Some species of molossids have a distinctive wrinkled upper lip, while others have a smooth upper lip. Muzzles of all these bats are generally short and wide and often have wide, fleshy lips that may have folds or creases. Many have a distinctive pad over their noses. The upper surface of this pad often has small horn-like projections. Ears of free-tailed bats are relatively short and thick, often joined across the forehead and point directly forward. The eyes of these bats are relatively small, while the lips are large. All species have long and narrow wings that are thick and, along with the tail, are covered in a leathery membrane. Molossids also have short, strong legs and broad feet. On the outer toes of each foot are curved bristles that the bat uses for grooming its fur.

Molossids generally have short, velvety fur. One group of bats in this family is called the hairless bats because their hair is so short that the animal appears to be naked. Some species have a crest of hairs on the top of the head that stands upright. Fur color may be gray, tan, black, or brown. Many species have two color phases, or types, a reddish one and brownish or blackish color phase.


Molossids are found throughout the world’s warmer areas. They are primarily found in South America and Africa, as well as from southern Europe and southern Asia through Malaysia, and east to the Fiji Islands. They are also found in the central and southern part of the United States, south through the West Indies, Mexico, and Central America to the southern half of South America. Except for one other family of bats, the Vespertilionidae, molossids are found in the widest geographic area.


With molossids spread out all over the world, they are found living in a wide range of habitats. They are commonly found in both natural and urban areas. These bats are most plentiful in arid (extremely dry) and semi-arid conditions. They prefer to live in temperatures that are at least 110°F (43°C). These bats roost (rest or settle) in sites such as caves, tunnels, buildings, hollow trees, foliage, decayed logs, and holes in the ground. They also shelter under bark, rocks, and iron rooftops.


Molissids eat a variety of insects, such as moths and ones with hard shells, such as beetles and stinkbugs.


Molossids are generally strong flyers that can fly quickly for long periods of time. Like all bats, these bats are nocturnal, meaning they are active at night. These bats fly all night, whereas other bats typically fly a short time during the night. They can fly six or seven hours without stopping.

Molossids catch their prey using echolocation (eck-oh-lohKAY-shun), a technique where the bat detects objects by receiving the reflection of sounds it produces. They fly with their mouths open and send out echolocation calls. They forage, search for food, in groups and head towards large swarms of insects. They also look for food around streetlights, which attract insects, such as moths. They generally catch their prey while they are flying.

Because they live in warm areas, molossids do not need to hibernate (become inactive in the cooler months to conserve energy). Some of these bats travel to even warmer areas in the winter.

Molossids have a range of roosting habits, from solitary to social, living in large colonies (groups) of millions of individuals. Between those two extremes, sizes of colonies range from hundreds to thousands of individuals. Most of these bats do form colonies in the size of a few tens to several hundred individuals. Molossids generally return to their roosting sites every year. Their colonies generally give off a strong, musky odor.

Little is known about the mating habits of most molossids. Most species are considered polygynous (puh-LIJ-uh-nus), meaning the male mates with more than one female during the mating season. Females of most species appear to produce one offspring per year. Two young are born on rare occasions, and the black mastiff bat in Trinidad possibly has two litters per year. During pregnancy, females generally form maternity colonies that are separate from the males. In these colonies, females relocate and nurse their young independently.


Like many insect-eating bats, molossids eat many insects that humans consider to be pests. The one hundred million Mexican free-tailed bats that live in Texas in the summer eat an estimated 1,000 tons (907 metric tons) of insects each night, many of which destroy crops. In California and other areas, farmers build bats houses to attract these bats so they will eat the pests. People also collect the bat droppings (guano; GWAHno) of molossid bats that live in large colonies, using the guano as a fertilizer as it is rich in nitrogen. Some species of these bats have also been associated with spreading disease, such as rabies. Rabies is a viral infection that attacks the nervous system and can be deadly.

People have caused the decrease in population of molossids by destroying and disturbing their natural habitat. These bats have also been harmed through eating insects that have come into contact with pesticides, chemicals designed to control pests.


The survival of many of these species is under threat. The IUCN lists Gallagher’s free-tailed bat, Niangara free-tailed bat, and Wroughton free-tailed bat, as Critically Endangered, meaning they face an extremely high risk of extinction in the wild. The Incan little mastiff bat is listed as Endangered, meaning it faces a very high risk of extinction in the wild. Fifteen other species are listed as Vulnerable, meaning they face a high risk of extinction in the wild.