Bats are the only mammals which can fly although some mammals can glide. There are over 900 different species. Bats are the second largest group of mammals, after rodents and make up one fifth of the world's mammals. Bats live all over the world, except in very cold places. There are two main groups the large fruit bats or flying foxes, and the smaller insect-eaters. Some bats also feed on birds, lizards, fish, nectar and blood.