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 colony's nightly emergence drew television crews: Bracken Cave appeared in the pilot episode of Dirty Jobs and in the World's Weirdest episode 'Freaks of the Sky' on National Geographic Wild. The bats leave between 6 and 8 p.m., heading southeast after moths pushed off crops by winds.

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.

The colony is usually estimated at 20 million bats, but the true number is unknown because counting methods are unreliable. In the 1960s and 1970s, researcher Leonard Ireland described the emerging clouds as up to 30 miles long and 20 miles wide.