The Mexican Free-Tailed Bat, (Tadarida brasiliensis mexicana), is a subspecies of the Brazilian Free-Tailed Bat, (Tadarida brazilensis). The bat is called free-tailed because the last part of the tail is not enveloped in the back part of the wing as are most bats. This gives all free-tailed bats a distinctive short mouse-like tail. Bats are mammals but otherwise not related to the mouse. As mammals all bats are born live, attached to a placenta, just like the rest of us mammals. The pups suckle from the breast and are helpless.

The adult Mexican Free-Tailed Bat is about four inches long and weighs only about fifteen grams. The pup is the size of the end of your little finger. In the summer this bat can be seen in Texas, living in colonies of millions in caves and man-made structures such as bridges. Colonies of Mexican Free-Tailed bats are the largest in the world. Bracken Cave near San Antonio is said to be the summer home to up to ten million bats. These large colonies make an impressive sight as they swarm out in the evening going for their nightly feed.

In the winter the Mexican Free-Tailed Bats migrate south to Mexico and South America where they breed. Most of the male bats stay south when the pregnant females come back north to deliver and raise their pups. During their summer stay the female may move to different colonies several times. Going to a warmer “maternity’ colony to have her offspring. The pup, unable to fly, stays in the cave while the mother goes out to feed. It is amazing that the mother can find her pup among the millions of others, especially when you consider the pups don’t stay put very well.

The Mexican Free-Tailed Bat eats moderate size insects, especially moths. Many of these are serious agricultural pests. The bat will eat half its weight in insects nightly, nursing females even more. The ten million bats of Bracken cave are said to eat 250 tons of insects nightly.

The Mexican Free-Tailed Bats of the Devil’s Sinkhole have a unique problem. The huge cavern has a relatively small opening in the dome, only about fifty-five to seventy feet across. Flying straight up is difficult so the bats circle upwards in a counter clockwise direction. This column of swirling bats gets literally squeezed into a small spinning column as they emerge from the opening. To the onlooker it is like a dark tornado that lasts about forty-five minutes. Wow!