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
Mexican free-tailed bat bats. Their ears are wide, rounded, and large compared to their head, nearly meeting at the front of the face but distinctly not joined at the midline and projecting anterodorsally from just before the muzzle to the back of the head. They use their large ears to help them find prey using echolocation. "T. brasiliensis" is distinguished among North American Tadarida bats in possessing deep wrinkles on the upper lip and in having a Z-shaped upper third molar which is used for grinding insects. These individuals possess canines which are larger in males than in females. The wings are elongated