Bats are a group of winged mammals that constitute Chiroptera, the second-largest order of mammals after rodents (order Rodentia). The order accounts for about 20% of all classified mammal species worldwide, with around 1,500 known species. These mammals are found worldwide except Antarctica and some extremely isolated oceanic islands, such as Iceland, where no native populations are found.
Bats are the only mammals capable of true, sustained flight, whereas animals like colugos and sugar gliders can only glide through the air. Their flight is powered by a pair of membranous wings, which are nothing but modified forelimbs.
Traditionally, bats have been grouped into megabats and microbats, a classification that reflects their diverse dietary patterns, with megabats mainly feeding on fruit and nectar, while microbats are predominantly insectivorous. Many microbats hunt in the dark by emitting high-frequency calls and interpreting the returning echoes (echolocation), which helps them detect and capture prey with remarkable precision even when vision is limited.
As many bats are insectivorous, they help control insect pests, reducing the need for chemical pesticides. However, a few species (less than 1% of all bats) serve as natural reservoirs for pathogens, such as the rabies virus, thereby transmitting the disease when in close contact with humans.
Bats exhibit one of the widest size ranges among mammals, with the smallest species, the Kitti’s hog-nosed bat, measuring only a few millimetres in length, while one of the largest, the giant golden-crowned flying fox, has a wingspan almost equal to the height of an adult human.
They have a basic mammalian body plan, comprising a head, neck, trunk, two forelimbs modified into wings, two hindlimbs, and a tail (in most species). The five digits of the forelimbs are elongated, and a thin wing membrane (patagium) stretches from the arm and finger bones to the side of the body and the hindlimbs. The patagium is dotted with touch-sensitive receptors on specialized epithelial cells (Merkel cells). It is usually divided into the following parts:
All bats have strong claws on the toes of the hind feet. These claws are designed for gripping, especially for hanging upside down from branches, cave ceilings, and rock surfaces. Most bats also have a claw on their thumb.
Megabats generally have a fox-like skull shape, having a long snout and prominent ears, while in microbats, skull shape varies more noticeably with diet. For example, species that feed on nectar tend to have elongated snouts, which help them reach deep into flowers, while vampire bats show the opposite trend, having reduced and shorter snouts.
Their dentition also varies with diet. Many small insect-eating species have a comparatively high tooth count (up to 38 teeth), whereas vampire bats typically have fewer teeth, usually around 20.
The name of the bat order, Chiroptera, derives from the ancient Greek words kheír (meaning ‘hand’)and pterón (meaning ‘wing’), hinting at the modification of their forelimbs into wings. The order was initially classified under the superorder Archonta, along with the treeshrews, colugos, and primates. However, recent genetic evidence reveals that their sister taxon is Ferungulata, a group comprising carnivorans, pangolins, odd-toed ungulates, and even-toed ungulates.1
A 2011 study categorized all bats into two major groups: Megachiroptera, comprising megabats, and Microchiroptera, comprising microbats. Megabats are mostly fruit- and nectar-eating bats that usually rely on strong vision and smell to forage, so most of them do not echolocate. In contrast, microbats are mostly insect-eating and depend heavily on echolocation to move through the dark and locate prey.
Further phylogenomic studies revealed that megabats are nested within microbats. As a result, 2 new suborders were proposed in 2013: Yinpterochiroptera (which includes the megabats) and Yangochiroptera. The 2 suborders are further classified into 21 families.
Since bats have delicate skeletons, they do not fossilize well, with only 12% of bat genera represented in the fossil record. The oldest bat fossils, Archaeonycteris praecursor and Altaynycteris aurora, date back ~56 million years ago, and both are known only from isolated tooth remains. However, complete bat skeletons were first discovered in Wyoming, belonging to the two species Icaronycteris gunnelli and Onychonycteris finneyi (~52 million years ago).
Bats occupy almost every continent, but their habitats vary with species and at different times of the year.
Roost sites may be found in tree hollows and cavities, such as those of the little brown bat (Myotis lucifugus), or in dense foliage, like palm fronds. Some fruit bats, such as the greater short-nosed fruit bat (Cynopterus sphinx), even build roost ‘tents’ by severing stems and folding leaves of creepers.2 Quite in contrast, some species, such as the straw-colored fruit bat (Eidolon helvum), generally roost openly in trees, often in large colonies.
In temperate regions, many species, such as the little brown bat, migrate to winter hibernation dens, which are primarily caves and mines, where they survive on stored fat.3
Bats show remarkable diversity in their dietary choices, ranging from insects and plant matter to vertebrates and animal blood.
Bats are attacked by a range of predators, especially when they are roosting, foraging at dusk, or leaving caves in large groups. They are most frequently preyed upon by raptors, such as owls, falcons, and hawks. Occasionally, snakes also kill bats, particularly when they are resting or when their young fall from roosts. Moreover, opportunistic predators, such as raccoons, weasels, and domestic cats, also feed on bats.
On average, most bats live6 between 10 and 20 years in the wild. However, the longest-living bat7 (as recorded in November 2005), a Brandt’s bat (Myotis brandtii) discovered in a cave in Siberia, was aged to be at least 41 years old. In fact, 13 members of the genus Myotis have been documented to live over 20 years in the wild.
Thus, bats live far longer than similarly sized mammals.
Most bats are polygynous, meaning males mate with multiple females, but in some species, like the Mexican free-tailed bat (Tadarida brasiliensis), both sexes mate with multiple partners. A few, like the yellow-winged bat (Lavia frons), are monogamous, forming long-term pair bonds.
Bats in temperate regions typically breed from late summer through autumn, while many tropical species breed more flexibly, often reproducing multiple times a year. During the breeding season, males of many bat species produce specialized courtship calls (songs) to attract females. One of the most notable examples is the Mexican free-tailed bat, whose males emit a complex mix of chirps, buzzes, and trills.8
Females of some bat species show delayed fertilization, storing sperm for months after mating. For example, little brown bats mate in late summer to early autumn, but fertilization occurs only after females emerge from hibernation in late winter or early spring.9 Other species, such as the greater horseshoe bat (Rhinolophus ferrumequinum), exhibit delayed implantation, where fertilization occurs after mating but the embryo implants only when conditions become favorable.10
Depending on the species, female bats undergo a gestation period of 40 to 60 days. However, the longest gestation period is that of the common vampire bat (Desmodus rotundus), spanning 7 to 8 months.11
Females give birth to live pups, typically one per litter, which are blind and largely hairless. These pups develop wings, learn to fly, and are eventually weaned.
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