the pentadactyl limb, only in their case the forelimb has been adapted as a wing. Among the intriguing features of bats is their use of acoustic orientation, or echolocation, to find their way through the dark caves and nocturnal exteriors that make up their world. Contrary to popular belief, they are not blind, but they do have very small eyes, simply because vision is not important for bat navigation. (See Migration and Navigation for more about this subject.) As befits an order with such a wide array of species, bats run the gamut with respect to their eating habits. The majority of bat species are insectivores that consume many thousands times their weight in insects each year. Many others are fruit bats, important members of the ecosystems they occupy, because they consume fruit and spread seeds, helping assist in seed dispersal . (Some bats also aid in pollination ; see Reproduction). Then there are the three species of vampire bat, which are largely responsible for bats' unfortunate reputation with humans. Members of subfamily Desmodontinae, species of vampire bat include Diaemus youngi and Diphylla ecaudata. However, the best-known variety is the common vampire bat, Desmodus rotundus, which is native to an area that stretches from the southwestern United States to the northwestern third of South America. As one would suspect of a creature named vampire, they live off blood, which they suck at night from birds or other mammals, including humans. These creatures are livestock pests and strike fear in humans