MEXICAN FREE-TAILED BAT: I vant to suck your blood! Oh relax. The Mexican free-tailed bat is far more interested in insects than our bodily fluids. Why free-tailed? Because unlike most bats, its wing membrane does not extend past the midpoint of its tail. This puts it at a disadvantage when trying to net insects on the fly. It makes up for this shortcoming with its incredible speed; this medium-sized bat has been clocked at 60 mph or more. It lives in caves in the southern United States, Mexico, the West Indies and northern South America. A few of these colonies are the largest congregations of mammals in the world. The largest of these is a maternity colony in Bracken Cave, which is located just north of San Antonio, Tex. Around 20 million bats roost here during the summer, eating up to 250 tons of insects per night. It finds insects by bouncing high-frequency sounds off objects in the environment in a process called echolocation. It emit sounds from its leaf-shaped nose and listens for the echos with its large, hyper-sensitive ears. In this way it can zero in on tasty moths in the pitch dark.