Bracken Cave, Natural cave system in Comal County, Texas, US

Bracken Cave is a natural cave system in Comal County, Texas, known for hosting the largest bat colony on Earth. The entrance opens as a crescent-shaped gap at the base of a sinkhole created when the roof collapsed over time.

Bat Conservation International purchased the site in the early 1990s to protect the colony from disturbance and development. Since then, the area has served as a sanctuary where access is limited to preserve the bats during their breeding season.

The cave appears in National Geographic Wild's 'World's Weirdest' series, showcasing natural phenomena to television audiences worldwide.

Visitors who are members of the conservation organization can join guided evening tours from March through October, when millions of bats leave the cave at dusk. It helps to arrive early to find a good viewing spot before the animals begin their nightly departure.

During summer months, up to 15 million Mexican free-tailed bats leave the cave at the same time to feed on insects over the surrounding plains. This nightly flight takes several hours and appears on weather radar as a dense cloud moving across the sky.