The bat order is divided on anatomical grounds into two major divisions, or suborders: the Megachiroptera, or fruit bats, found only in the Old World tropics, and the Microchiroptera, or insect-eating bats, with a worldwide distribution. The fruit bats include the largest species of bat, the flying foxes, which may weigh 2 or 3 lbs (.9 to 1.4 kg). Their diet is confined almost entirely to fruit, nectar, and pollen. The insect-eating bats include the smallest bat species. Despite the name, some of these bats live wholly or largely on fruit; a large number eat insects and, in some cases, larger animals. Members of several species catch fish as they skim over water, and the South American vampire bats feed exclusively on blood.
The most common bats of the temperate Northern Hemisphere are the Old World horseshoe bats ( Rhinolophus ), characterized by one or two horseshoe-shaped facial appendages, the cosmopolitan little brown bats ( Myotis ), big brown bats, or serotines ( Eptesicus ), and pipistrelles ( Pipistrellus ). The last three, all represented by species in North America, belong to the plain-nosed bat family (Vespertilionidae), characterized by a lack of appendages on the snout.
There are over a dozen species of Myotis in North America; the common little brown bat, M. lucifugus, is distributed over the entire continent from Alaska and Labrador to the S United States. A colonial bat, it is found in many habitats, including houses. It is about 21/2 in. (6.3 cm) long without the tail and weighs about 1/4 oz (7 grams). The North American big brown bat, Eptesicus fuscus, of similar distribution, is about three times as heavy, with a wingspread of 12 in. (30 cm). The little and big brown bats are among the species susceptible to white-nose syndrome, which leads to water loss and emaciation during winter hibernation. Identified in 2006 and caused by the fungus Geomyces destructans, it has been devastating to bat colonies in North America. Large, solitary North American bats of wide distribution are the hoary bat, Lasiurus cinereus, yellow-brown with silver frosting, and the red bat, L. borealis, which is a striking brick-red color. Both have soft, thick fur and roost in trees.
The freetail bats (family Molossidae) are a cosmopolitan group of communal bats characterized by a long tail extending well beyond the end of the tail membrane. Among them are the guano bats ( Tadarida ), which live in enormous colonies. Their excrement, called guano, accumulates in great quantities in their roosting places and is commercially valuable as fertilizer. Most New World freetail bats are tropical, but several are found in the S United States. One of these, the Mexican freetail bat ( Tadarida brasiliensis ), is noted for its colonies in the Carlsbad Caverns of New Mexico, numbering an estimated 250,000 to 500,000 individuals. When these bats leave the caves together it takes about 20 min for the entire column to make its exit. This family also includes the mastiff bats ( Eumops ), largest of the North American bats, with a wingspread of 18 in. (46 cm).