The megabat, contrary to its name, is not always large: the smallest species is 6 cm (2.4 in) long and thus smaller than some microbats. The largest attain a wingspan of 1.7 m (5.6 ft), weighing in at up to 1.6 kg (3.5 lb). Most fruit bats have large eyes, allowing them to orient themselves visually in twilight and inside caves and forests.
Megabats make up the only family (Pteropodidae) in order Chiroptera that is not capable of laryngeal echolocation. Echolocation and flight evolved early in the lineage of Chiropterans and echolocation was later lost in family Pteropodidae. Both echolocation and flight are energetically expensive processes for bats. The nature of the flight and echolocation mechanism of bats allows for creation of echolocation pulses with minimal energy use. Energetic coupling of these two processes is thought to have allowed for both energetically expensive processes to evolve in bats. It is hypothesized that the loss of echolocation is due to the uncoupling of flight and echolocation in megabats. The larger average body size of megabats compared to echolocating bats  suggests that a larger body size disrupts the flight-echolocation coupling and made echolocation too energetically expensive to be conserved in megabats.
Behavior and ecology
Megabats are frugivorous or nectarivorous, i.e., they eat fruits or lick nectar from flowers. Often the fruits are crushed and only the juices are consumed. The teeth are adapted to bite through hard fruit skins. Large fruit bats must land to eat fruit, while the smaller species are able to hover with flapping wings in front of a flower or fruit.
Frugivorous bats aid the distribution of plants (and therefore, forests) by carrying the fruits with them and spitting the seeds or eliminating them elsewhere. Nectarivores actually pollinate visited plants. They bear long tongues that are inserted deep into the flower; pollen passed to the bat is then transported to the next blossom visited, thereby pollinating it. This relationship between plants and bats is a form of mutualism known as chiropterophily. Examples of plants that benefit from this arrangement include the baobabs of the genus Adansonia and the sausage tree (Kigelia).
As disease reservoirs
Fruit bats have been found to act as reservoirs for a number of diseases which can prove fatal to humans and domestic animals, but the bats themselves sometimes have no signs of infection.
Researchers tested fruit bats for the presence of the Ebola virus between 2001 and 2003. Three species of bats tested positive for Ebola, but had no symptoms of the virus. This indicates the bats may be acting as a reservoir for the virus. Of the infected animals identified during these field collections, immunoglobulin G (IgG) specific for Ebola virus was detected in Hypsignathus monstrosus (Hammer-Headed Bat), Epomops franqueti (Franquet's Epauletted Fruit Bat), and Myonycteris torquata (Little Collared Fruit Bat).
Other viral diseases which can be carried by fruit bats include Australian bat lyssavirus and Henipavirus (notably Hendra virus and Nipah virus), both of which can prove fatal to humans. These bats have been shown to infect other species (specifically horses) with Hendra virus in Australian regions. Later, humans became infected with Hendra virus after being exposed to horse body fluids and excretions.
Fox Island, Australia, is believed to be home to the largest colony of flying foxes on the continent.
Bats are usually thought to belong to one of two monophyletic groups, a view that is reflected in their classification into two suborders (Megachiroptera and Microchiroptera). According to this hypothesis, all living megabats and microbats are descendants of a common ancestor species that was already capable of flight.
However, there have been other views, and a vigorous debate persists to this date. For example, in the 1980s and 1990s, some researchers proposed (based primarily on the similarity of the visual pathways) that the Megachiroptera were in fact more closely affiliated with the primates than the Microchiroptera, with the two groups of bats having therefore evolved flight via convergence (see Flying primates theory). However, a recent flurry of genetic studies confirms the more longstanding notion that all bats are indeed members of the same clade, the Chiroptera. Other studies have recently suggested that certain families of microbats (possibly the horseshoe bats, mouse-tailed bats and the false vampires) are evolutionarily closer to the fruit bats than to other microbats.
^Monson, C. S.; Banack, S. A.; Cox, P. A. (2003). "Conservation implications of Chamorro consumption of flying foxes as a possible cause of amyotrophic lateral sclerosis-parkinsonism dementia complex in Guam". Conservation Biology17 (3): 678–686. doi:10.1046/j.1523-1739.2003.02049.x.
^Pettigrew JD, Jamieson BG, Robson SK, Hall LS, McAnally KI, Cooper HM (1989). "Phylogenetic relations between microbats, megabats and primates (Mammalia: Chiroptera and Primates)". Philosophical Transactions of the Royal Society B325 (1229): 489–559. Bibcode:1989RSPTB.325..489P. doi:10.1098/rstb.1989.0102.