There are about 1,200 species of bats in the world, Swartz says. Some eat fruit. Others eat insects or nectar(花蜜). And just a few drink blood.
Some bats use their eyes to see where things are .Others collect information about their surroundings by bouncing sound off objects and listening to the echoes.
But what all bats have in common (other than being the only flying mammals in existence) are flexible wings that enable them to change directions quickly. If you’ve ever seen bats darting(猛冲)through the air at dusk ,you probably noticed how abruptly they could change directions.
Scientists have long assumed that bats fly the same way as birds and insects do ---with rigid, airplane-like wings that hinge at the shoulder. The problem with that assumption, however, is that bats aren’t birds or insects. As mammals, they have more in common with people, horses,and dogs than with other flying creatures.
For example, birds have hollows bones, and insects have no bones at all. But most mammals have solid and heavy bones, which could make flying tough.
To solve this problem, bats have evolved strong and heavy bones near their shoulders, where they need more support. They’ve also saved some weight by developing lighter and weaker bones near the tips of their wings. The result is light but strong and very flexible.