Due to their physiology, bats are one type of animal that acts as a natural reservoir of many pathogens, such as rabies; and since they are highly mobile, social, and long-lived, they can readily spread disease among themselves.

[9][10] The extinct bats Palaeochiropteryx tupaiodon and Hassianycteris kumari, both of which lived 48 million years ago, are the first fossil mammals whose colouration has been discovered: both were reddish-brown.

[30][31] Myzopodidae Emballonuridae Nycteridae Mystacinidae Mormoopidae Phyllostomidae Furipteridae Noctilionidae Thyropteridae Natalidae Molossidae Miniopteridae Cistugidae Vespertilionidae Pteropodidae Hipposideridae Rhinolophidae Rhinonycteridae Craseonycteridae Megadermatidae Rhinopomatidae The molecular phylogeny was controversial, as it pointed to microbats not having a unique common ancestry, which implied that some seemingly unlikely transformations occurred.

[33] The second is that laryngeal echolocation had a single origin in Chiroptera, was subsequently lost in the family Pteropodidae (all megabats), and later evolved as a system of tongue-clicking in the genus Rousettus.

In general, megabats have longer snouts, larger eye sockets and smaller ears, giving them a more dog-like appearance, which is the source of their nickname of "flying foxes".

During embryonic development, the gene controlling Bmp signalling, Bmp2, is subjected to increased expression in bat forelimbs – resulting in the extension of the manual digits.

[67][68] For bat embryos, apoptosis (programmed cell death) affects only the hindlimbs, while the forelimbs retain webbing between the digits that forms into the wing membranes.

[76] Bats possess a highly adapted respiratory system to cope with the demands of powered flight, an energetically taxing activity that requires a large continuous throughput of oxygen.

[85] Vampire bats, probably due to their diet of blood, are the only vertebrates that do not have the enzyme maltase, which breaks down malt sugar, in their intestinal tract.

Carnivorous and vampire bats consume large amounts of protein and can output concentrated urine; their kidneys have a thin cortex and long renal papillae.

[93] In high-duty cycle echolocation, bats emit a continuous call and separate pulse and echo in frequency using the Doppler effect of their motion in flight.

The complex geometry of ridges on the inner surface of bat ears helps to sharply focus echolocation signals, and to passively listen for any other sound produced by the prey.

These ridges can be regarded as the acoustic equivalent of a Fresnel lens, and exist in a large variety of unrelated animals, such as the aye-aye, lesser galago, bat-eared fox, mouse lemur, and others.

[124][125] Scientists reported in January 2025 that they had discovered how bats travel hundreds of miles in the spring to give birth in warmer temperatures: they surf storm fronts.

[128] The largest bats are a few species of Pteropus megabats and the giant golden-crowned flying fox, (Acerodon jubatus), which can weigh 1.6 kg (3+1⁄2 lb) with a wingspan of 1.7 m (5 ft 7 in).

[138][139] Microbats are known to exhibit diurnal behaviour in temperate regions during summer when there is insufficient night time to forage,[140][141] and in areas where there are few avian predators during the day.

[147] The diet of an insectivorous bat may span many species,[154] including flies, mosquitos, beetles, moths, grasshoppers, crickets, termites, bees, wasps, mayflies and caddisflies.

[48][155][156] Large numbers of Mexican free-tailed bats (Tadarida brasiliensis) fly hundreds of metres above the ground in central Texas to feed on migrating moths.

They use echolocation to detect small ripples on the water's surface, swoop down and use specially enlarged claws on their hind feet to grab the fish, then take their prey to a feeding roost and consume it.

[187] The fungus was first discovered in central New York State in 2006 and spread quickly to the entire Eastern US north of Florida; mortality rates of 90–100% have been observed in most affected caves.

[189] Nova Scotia, Quebec, Ontario, and New Brunswick have witnessed identical die offs, with the Canadian government making preparations to protect all remaining bat populations in its territory.

[205][206] Their high mobility, broad distribution, long life spans, substantial sympatry (range overlap) of species, and social behaviour make bats favourable hosts and vectors of disease.

[220] Food sharing and mutual grooming may occur in certain species, such as the common vampire bat (Desmodus rotundus), and these strengthen social bonds.

[225] Among greater spear-nosed bats (Phyllostomus hastatus), females produce loud, broadband calls among their roost mates to form group cohesion.

[228] In the highly sexually dimorphic hammer-headed bat (Hypsignathus monstrosus), males produce deep, resonating, monotonous calls to attract females.

Male greater sac-winged bats (Saccopteryx bilineata) have sacs in their wings in which they mix body secretions like saliva and urine to create a perfume that they sprinkle on roost sites, a behaviour known as "salting".

[48] Female bats use a variety of strategies to control the timing of pregnancy and the birth of young, to make delivery coincide with maximum food ability and other ecological factors.

Other species exhibit delayed implantation, in which the egg is fertilised after mating, but remains free in the reproductive tract until external conditions become favourable for giving birth and caring for the offspring.

[278][279][280] An East Nigerian tale tells that the bat developed its nocturnal habits after causing the death of his partner, the bush-rat, and now hides by day to avoid arrest.

[289] The bat is sometimes used as a heraldic symbol in Spain and France, appearing in the coats of arms of the towns of Valencia, Palma de Mallorca, Fraga, Albacete, and Montchauvet.