Discover the Infested Texas Cave Swarming with 20 Million Bats

Written by Kellianne Matthews
Published: March 14, 2023
© U.S. Fish and Wildlife Service Headquarters / CC BY 2.0 – License / Original
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Beyond the city limits of San Antonio, Texas, lies a rather unassuming cave nestled in a large sinkhole. During the day it may not look like much, but as the sun sets, something truly magical happens. As day fades to dusk, a handful of bats begin emerging from the cave’s wide entrance. At first, just a few flutter out here and there, but slowly, their numbers begin to grow. Within minutes, the sky darkens with an enormous torrent of bats leaving the cave like a colossal, living tornado that continues to swarm for the next three to four hours. Some estimate the cave holds 20 million bats! It is a jaw-dropping sight and can only be witnessed firsthand at the incredible Bracken Cave in Texas. 

Bracken Cave

Mexican Free-tailed Bat
Mexican free-tailed bats are some of the fastest mammals in the world.

©Bureau of Land Management / CC BY 2.0 / flickr – License

This secluded area may be quiet during the winter months, but from March to October Bracken Cave transforms with an infestation of at least 15 to 20 million Mexican free-tailed bats! The cave sits at the bottom of a sinkhole in Comal County, Texas. Long ago a giant collapse tore open a 60-foot crescent-shaped opening into this unique underground area. Ever since, bats have been coming to nest here, as evidenced by the 10,000 years of guano deposits (aka, bat poop) all throughout the cave. Even today bats continue to flock to this ancient site year after year. 

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It’s hard to say exactly how many Mexican free-tailed bats (Tadarida brasiliensis) live in the cave each year. Leonard Ireland, an animal behavior expert, once said that you could see clouds of bats that stretched nearly 30 miles long and 20 miles wide that emerged from the cave. In addition, Mexican free-tailed bats are some of the fastest mammals in the world. They can fly up to 100 miles per hour in short bursts! So, you can imagine just how challenging it is to try to count each and every last bat at Bracken Cave!

Why Do Bats Come to Bracken Cave?

Mexican free-tailed bats spend their winters in Mexico where they breed. However, when spring comes male bats form bachelor colonies. Female bats fly as far as 1,000 miles to Texas and will spend the next several months in many of the caves there. 

Bracken Cave, however, hosts the largest of these Mexican free-tailed bat colonies. Bracken Cave provides an excellent sanctuary for female Mexican free-tailed bats to give birth and raise their young babies. The rock and soil of the cave provide plenty of insulation. And with millions of bats inside, the cave stays nice and warm at around 102 to 104 degrees Fahrenheit. 

Female bats set up a nice little nursery in the cave. Then, when the time comes, each female gives birth to a single baby bat called a pup. The hairless pink pups snuggle tightly together as they cling to the cave’s walls to stay warm — and there are a lot of baby bat pups. As many as 500 pups have been observed packed together in just one square foot of space along the wall! 

When the mother bats leave the cave in the evenings, they fly up to 60 miles away. The large group can consume over 100 tons of insects during their nightly excursions. In fact, just one female bat can eat nearly her entire body weight in bugs each and every night! Mexican free-tailed bats eat a wide variety of pesky insects that harm crops, such as army cut-worm moths, cotton bollworm moths, flying beetles, and winged ants. These nightly feedings provide some of the best pest control in town — and it’s 100% natural and doesn’t cost a cent! These Mexican free-tailed bats help local farmers save hundreds of thousands of dollars each year!

Protecting the Mexican Free-Tailed Bats in Bracken Cave

Bracken Cave acts as a vital habitat for millions of Mexican free-tailed bats

© – License

Bracken Cave acts as a vital habitat for millions of Mexican free-tailed bats, so Bat Conservation International purchased the cave and much of the land surrounding it in 1992. Over the years, the organization continued to make additional small land purchases to preserve and protect the bat’s natural habitat in and around Bracken Cave.

However, Central Texas began to see unprecedented growth during the next several years. A local company wanted to purchase some of the additional land surrounding the cave to build a large housing development. Fortunately, the cave and the land owned by Bat Conservation International would remain untouched. However, the proposal presented new threats to the Mexican free-tailed bats in Bracken Cave. Bats are attracted to both light and houses and often build nests in such structures. So, building a large housing complex so close to the cave would cause problems for both bats and human residents.

Unfortunately, people in urban areas often harm bat colonies out of fear or irritation — it’s not uncommon for them to cover caves with chicken wire or even set fire to them. Bat Conservation International feared that this could happen to the incredible bats of Bracken Cave. So, they began looking for ways to increase awareness and raise money to compete with the local developer. 

The Importance of Bracken Cave 

Councilman Ron Nirenberg in nearby San Antonio heard about the pressing conflict, so he decided to go and investigate for himself. After witnessing the spectacular display of bats emerging from the cave, Nirenberg joined the fight to protect the bats and create a protective buffer zone around the cave.

Nirenberg explained that this secluded landscape is not only a safe haven for bats but for other animals as well. In addition, the area is pivotal to the Edwards Aquifer — a vital source of water for much of San Antonio’s population. Furthermore, the presence of bats saves millions of dollars each year that would otherwise be spent on crop damage and pesticides. 

With Nirenberg’s support and the help of many generous donors, Bat Conservation International and The Nature Conservancy were able to purchase the land — which was now available, as the local developer bowed out due to public pressure.

The unified groups made the 20 million-dollar agreement in 2014. Now the bats of Bracken Cave are safe from development and human encroachment. In addition, the agreement protects the bats from light pollution near the cave, allowing the area to stay dark at night. The agreement protects the city’s groundwater supply, local farmers, the habitats of endangered golden-cheeked warblers, and of course, the Mexican free-tailed bats of Bracken Cave. 

Bat-Watching in Texas

Congress Avenue Bridge
At the Congress Avenue Bridge in Austin, over one million bats swarm each evening throughout the summer.

©Kushal Bose/

Today, Bat Conservation International manages and protects 1,458 acres of the Bracken Cave Preserve. The Nature Conservancy also purchased and protects 1,521 acres of nearby land as well. In an effort to keep this extraordinary and vulnerable bat colony safe and secure, Bat Conservation International restricts access to the cave. However, small groups are welcome a few nights each week in an area nearby. With an advanced reservation, they can witness the phenomenal tornado of millions of bats swarming from Bracken Cave.

In addition to Bracken Cave, there are many other popular areas in Texas where people come to see colonies of Mexican free-tailed bats. For example, at the Congress Avenue Bridge in Austin, over one million bats swarm each evening throughout the summer. Austin also hosts a yearly “Bat Fest” with all sorts of fun activities. The celebration includes live music, food, vendors, and educational presentations in honor of the bats. Bat caves at the Eckert James River Bat Cave Preserve and Old Tunnel State Park also offer opportunities to learn more about these fascinating creatures of the night and their value to the local ecosystem. 

Wildlife in and Around Bracken Cave

Golden-cheeked Warbler
The population of golden-cheeked warblers is extremely unique, as these birds only nest in Central Texas!

©Michael Armentrout/

In addition to the massive Mexican free-tailed bat colony, the Bracken Cave Preserve and its surrounding landscape also provide homes to many other animals like squirrels, deer, ringtail cats, coyotes, bobcats, and skunks. There are also at least 43 bird species, including the federally endangered golden-cheeked warbler. The population of golden-cheeked warblers is extremely unique, as these birds only nest in Central Texas! Golden-cheeked warblers enjoy warm winters in Mexico but spend the rest of the year in Texas where they breed and nest. 

The Bracken Cave Preserve also works to protect and provide appropriate habitats for golden-cheeked warblers. Golden-cheeked warblers have very exclusive habitat needs, relying on juniper, oak, and cedar bark to build their nests. Their breeding range in Texas is also extremely limited. 

Many areas were once viable habitats for these birds. However, humans cleared these areas for buildings, roads, and stores, or used them to cultivate crops and grass for livestock. The timber industry also harvested juniper trees — the bird’s primary nesting grounds — for several decades. In addition, the construction of large lakes in Texas also flooded several of their woodland habitats. 

However, Bat Conservation International and The Nature Conservancy are dedicated to restoring and protecting the environments in and around Bracken Cave. Their efforts will hopefully help to secure a much brighter future for populations of Mexican free-tailed bats, golden-cheeked warblers, and many of the other amazing animals in Central Texas!

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The Featured Image

Mexican free-tailed bats exiting Bracken Bat Cave
Mexican free-tailed bats exiting Bracken Bat Cave
© U.S. Fish and Wildlife Service Headquarters / CC BY 2.0 – License / Original

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About the Author

As a professional writer and editor for many years, I have dedicated my work to the fascinating exploration of anthrozoology and human-animal relationships. I hold a master's degree with experience in humanities, human-animal studies, ecocriticism, wildlife conservation, and animal behavior. My research focuses on the intricate relationships and dynamics between humans and the natural world, with the goal of re-evaluating and imagining new possibilities amid the uncertainty and challenges of the Anthropocene.

FAQs (Frequently Asked Questions) 

Why is Bracken Cave important?

Bracken Cave hosts the largest bat colony in the world! There are 15 to 20 million Mexican free-tailed bats that live inside the cave. It is also a vital nesting site for the bats, who give birth and raise their pups in Bracken Cave.

Bats are vital pollinators for many crops across the world and are some of the most effective pest-controllers out there. The presence of bats near farms can save millions of dollars each year — and farmers do not have to use harmful pesticides!

In addition, bats are threatened all across the world due to habitat loss and white-nose syndrome (WNS), which kills bats while they are hibernating. WNS has killed over five million hibernating bats across 19 states in the U.S. and has been known to devastate entire populations of bats in a short amount of time. Fortunately, the bats at Bracken Cave have remained free from WNS, and Bat Conservation International is continuing to restore and protect their habitat in Texas.

When are there bats at Bracken Cave?

Bats travel to Bracken Cave in Texas and nest there from March through October. The rest of the year they live in Mexico.

When can you see bats at Bracken Cave?

Reservations to see bats at Bracken Cave are available from May through August.

How can you see the bats at Bracken Cave?

If you want to see the bats in Bracken Cave, you’ll have to make a reservation through Bat Conservation International in advance. Be sure to plan ahead, as reservations are limited so as not to disturb the bats.

How big are Mexican free-tailed bats?

Mexican free-tailed bats are pretty small. Their wingspan measures around 12 to 14 inches, and they only weigh 0.4 to 0.5 ounces.

Are Mexican free-tailed bats blind?

No! Mexican free-tailed bats are not blind, even though they are often portrayed that way. In fact, they can see quite well — they utilize echolocation to help them see and perceive the world around them even better!

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