Bats are mammals in the order Chiroptera (pronounced /kaɪˈrɒptərə/). The forelimbs of bats are developed as wings, making them the only mammals naturally capable of flight (opposed to other mammals, such as flying squirrels, gliding possums and colugos, that glide only for a distance). Bats do not flap arms like birds, instead they flap spread out hands where their fingers are very long and covered with a thin membrane or patagium. Chiroptera comes from two Greek words cheir (χειρ) "hand" and pteron (πτερον) "wing."
There is an estimated total of about 1,100 species worldwide, which is about 20 percent of all classified mammal species. About 70 percent of bats are insectivores. Most of the rest are frugivores, with a few species being carnivorous. Bats are present throughout most of the world and perform a vital ecological role by pollinating flowers, and eat various plants to dispere their seeds. Many tropical plants depend for their seeds to be distributed entirely by bats.
Bats range in size from Kitti's Hog-nosed Bat measuring 29–33 mm (1.14–1.30 in) in length and 2 g (0.07 oz) in mass, to the Giant golden-crowned flying fox which has a wing span of 1.5 m (4 ft 11 in) and weighs approximately 1.2 kg (3 lb).