Bat prevent them from spending too much time in unfamiliar places, and decrease predation. In some species, pregnant individuals may not use torpor. The smallest bat is Kitti's hog-nosed bat ("Craseonycteris thonglongyai"), which is long with a wingspan and weighs . It is also arguably the smallest extant species of mammal, next to the Etruscan shrew. The largest bats are a few species of "Pteropus" megabats and the giant golden-crowned flying fox, ("Acerodon jubatus"), which can weigh with a wingspan of . Larger bats tend to use lower frequencies and smaller bats higher for echolocation; high-frequency echolocation is better at detecting
Bulldog bat are long and narrow and their ears are large and funnel shaped. Unusual among bats, they have cheek-pouches for storing food. They also have full lips divided by a fold of skin giving a 'hare lip' look which together with the cheek pouches gives them their bulldog-like appearance. The species of lesser bulldog bats are insectivorous and whilst the greater bulldog bats also eat insects their chief food is fish. They use their echolocation to pinpoint the ripples they make on the surfaces of water. The greater bulldog bat trawls the water with its long, curved talons approximately 2–3 cm