Weighing in at 0.05 to 0.07 ounces, with a head-to-body length of 1.14 to 1.29 inches and a wingspan of 5.1 to 5.7 inches, the bumblebee bat—also known as Kitti’s hog-nosed bat—is the smallest mammal in the world, according to the Guinness Book of World Records. To see this tiny bat for yourself, you’d have to visit one of a select few limestone caves on the Khwae Noi River in Kanchanaburi Province of southwest Thailand. Here are more of Earth’s tiniest creatures that play a big role in the environment.