Which cave in Texas is the summer home to the largest bat colony in the world?

Bracken Cave in Texas is the summer home of the world's largest bat colony. Located in southern Comal County near San Antonio, the cave shelters millions of Mexican free-tailed bats from roughly March through October.

The cave sits beneath a broad sinkhole created when part of its roof collapsed. Estimates commonly put the seasonal colony at about 20 million bats, although the exact number is difficult to determine because counting a moving cloud of bats is unreliable. The migrants travel from Mexico to Texas, where females give birth to pups before the colony returns south in autumn.

At dusk, the bats stream from the entrance in a spectacular spiral and then spread across the surrounding countryside to hunt insects. Their feeding helps control agricultural pests and has been valued for its benefit to cotton farmers. Access is restricted because the cave and its surrounding habitat are vulnerable to disturbance.

Mammoth Cave and Carlsbad Caverns are much more famous cave systems, but neither is the principal summer roost of this enormous bat colony.