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
Echolocation jamming produce ultrasonic clicks in response to the echolocation calls bats use while attacking prey. For most species of tiger moth these clicks warn bats that the moths have toxic compounds that make them distasteful. However, the tiger moth "Bertholdia trigona" produces clicks at a very high rate (up to 4,500 per second) to jam bat echolocation. Jamming is the most effective defense against bats ever documented, with jamming causing a ten-fold decrease in bat capture success in the field. The possibility that moths jam bat echolocation arose with an experiment report published in 1965 by Dorothy Dunning and Kenneth Roeder.