The smallest bat in the world is the bumblebee bat, also known as Kitti's hog-nosed bat. It weighs just about two grams, or .07 ounces. It is considered the smallest mammal in the world, based on skull size, though the Etruscan shrew weighs slightly less.
The bumblebee bat is found in Thailand and Burma, living in limestone caves near rivers. Colonies number anywhere from 10 to 500 individual bats. They are typically active for less than an hour every day, coming out for about 30 minutes in the evening and 20 minutes at dawn to forage for insects. As of 2014, the bumblebee bat is vulnerable and may be at risk for extinction, primarily because of loss of habitat and disturbance of roosting sites.