Brazilian (Mexican) free-tail bats eat insects, typically moths and beetles. Studies examining insect remains in free-tailed bat guano rarely, if ever, encounter evidence of mosquito consumption. Some other bat species do eat mosquitoes, however. A pregnant or lactating bat can eat from 50 to 100 percent of her body weight in insects each night. It is estimated that 100,000 bats can eat more than 1,000 pounds of insects each night.
They can catch prey directly in their mouth and/or by using their tail membrane or wings to assist in capturing the flying insects. Like many bats, they use echolocation to detect and catch the insects. The free-tailed bats have been observed feeding 36 miles from the Cavern. They have been found in every direction from the park. Typically they head to a water source after emergence.
Not far away in Texas, Brazilian free-tail bats have been documented feeding on insects at 10,000 feet. At this altitude, they are following and eating cotton bollworm moths (aka corn earworm moth), army cutworm moths, tobacco budworm moth, and other costly agricultural pests. They can fly at speeds of up to 60 mph. When the bats are emerging from the cavern, they can be traveling at around 35 mph. Unlike many other bat species, they typically do not use night roosts. They fly all night, except the moms that come back to feed their pups during the night.