Its proclivity towards roosting in huge numbers at relatively few locations makes it vulnerable to habitat destruction in spite of its abundance.

[7] Mexican free-tailed bats are typically 9 cm (3.5 in) in length and weigh around 7–12 g (0.25–0.42 oz) with females tending to be slightly heavier than males by 1–2 grams for increased fat storage to use during gestation and nursing.

[8] Their tails are almost half their total length and stretch beyond the uropatagium, giving them the name "free-tailed" bats.

[8] The wings are elongated and narrow with pointed tips, making them well-equipped for quick, straight flight patterns.

[8] The bats can make roosting sites of buildings regardless of "age, height, architecture, construction materials, occupancy by humans and compass orientation".

Caves in Florida tend to have pools of water on the floor and the free-tailed bats do not need as much relative humidity as the southeastern myotis.

[8] Some bat populations in other areas of North America do not migrate, but are residents and may make seasonal changes in roost sites.

[14] Bats ranging eastward from East Texas do not migrate, but local shifts in roost usage often occur seasonally.

The bats eat moths, beetles, dragonflies, flies, true bugs, wasps, and ants.

[15] Large numbers of Mexican free-tailed bats fly hundreds of meters above the ground in Texas to feed on migrating insects.

[19] T. brasiliensis bats spend around 60% of their active time foraging while aerial, mostly hunting at heights of 6–15 m (20–49 ft).

WNS can affect T. brasiliensis, but has yet to be greatly introduced to their habitat due to their preference for more arid caves.

The chemical nonanal is found in such a concentration that its antimicrobial activity can inhibit the growth of two fungal pathogens that cause ringworm (Trichophyton mentagrophytes and T. rubrum), as well as Malassezia furfur, a yeast.

Two other common skin disease-causing microbes that are inhibited by the hair's concentration of nonanal include Staphylococcus aureus and Cutibacterium acnes.

This allows the bats to filter out a large majority of inhaled ammonia before it reaches toxic levels in the blood.

T. brasiliensis bats are thought to swarm in spiraling motions within caves to ventilate ammonia and renew the air.

[29] On 6 November 2014, Aaron Corcoran, a biologist at Wake Forest University, North Carolina, reported online in Science that his team and he had detected Mexican free-tailed bats emitting ultrasonic vocalizations that had the effect of jamming the echolocation calls of a rival bat species hunting moths.

The 'jamming' call led to an increased chance of the rival missing its prey, which the Mexican free-tailed bat was then able to eat itself.

During passive copulation, the males simply flies to a female in her roost and quietly mounts her with no resistance.

[34] A mother will nurse her young daily, and by 4–7 weeks old they are full grown, fully weaned, and independent.

For instance, during the spring and summer, one of the largest Mexican free-tailed bat populations inhabits Cueva de la Boca, a cave near Monterrey, Mexico.

Because of a reduction by more than 95% of the original 20 million bat population to 600,000, as a result of vandalism, pollution, and uncontrolled tourism, the organization decided to buy the property to place it under conservation.

BCI planned to revert any land changes that were a result of farming or ranching in order to conserve the biodiversity and wildlife there.

Preserving the land around Bracken Cave was important, as it is home to the world's largest bat colony, and any human encroachment would be detrimental to their population.

In 1863, a gun powder factory opened near San Antonio, the saltpeter of which was provided by local guano mines.