Mexican Free Tailed Bats

Tadarida brasiliensis

All about the Mexican Free-Tailed bat

“RABIES! Rabies! Rabies! Rabies!” Who can forget this screechy line from Stef in The Goonies?  Since the mid 20th century, a sort of paranoia surrounding rabies has persisted throughout the world. Although it is not a disease that is often transmitted through bats, they are known to be carriers. Over the last 50 years there have only been a few dozen reports of rabies transmission through bats. In the 1950s the Mexican Free-Tailed bat was thought to transmit airborne rabies to humans, but this myth was quickly debunked.

What does a Mexican Free-Tailed bat look like?

Mexican Free Tailed Bat

Mexican Free Tailed Bat

About 3.5 inches in length, the Mexican Free-Tailed bat (sometimes called the Brazilian Free-Tailed bat) weighs approximately a ½ ounce. The tail of the Mexican Free-Tailed bat makes up almost half its length, extending beyond the uropatagium (the portion of the body between the two hind limbs). This is where the Free-Tailed bat gets its name. The Mexican Free-Tailed bat has reddish, dark brown, or gray fur with black ears and tails. Well-equipped for rapid, direct flight the Free-Tailed bat has long, narrow, pointed wings and wrinkly lips. These bats also have wide, far-set ears that particularly help with echolocation.

Where does the Mexican Free-Tailed bat live, and what does it eat?

The Mexican Free-Tailed bat is one of the most abundant mammals in North America. They are found in the western and southern U.S., south through Mexico and Central America, and into the northern parts of South America. Roosting in large numbers in only a few roosts, though, has led to a decline in Mexican Free-Tailed bat numbers in Utah and California. Interestingly, the bat is the “official state bat” of both Oklahoma and Texas and you can see it featured on the labels of Bacardi rum.

The favorite roost of the Mexican Free-Tailed bat is in caves, but they have also been known to roost in manmade structures like attics of houses, under bridges, in dark recesses of ceilings and walls, and bell towers of churches. The roost of the Mexican Free-Tailed bat is one of the largest of the species, containing as many as a million bats in one roost. For this reason caves and hollowed out trees like mangroves and the cypress make suitable roosts for the Free-Tailed bat. The Mexican Free-Tailed bat prefers a habitat with low humidity that is cool and dark near a source of water.

Mexican Free Tailed Bats Texas

Mexican Free Tailed Bats living underneath a freeway overpass

Mexican Free-Tailed bats are insectivores, consuming enormous amounts of insects:  primarily moths but also mosquitoes, gnats, mayflies, beetles, dragonflies, lacewings, and wasps. The Free-Tailed bat will fly tens of meters above ground to prey on insects in flight. In some large roosts, an estimated 250 tons of insects are consumed every night by the Mexican Free-Tailed bat. The bat uses echolocation to find its prey in the dark then tucks it into a pouch made with its wing. Once it is trapped, the bat will grab the prey and eat it. Mexican Free-Tailed bats, while pesty if roosting in manmade structures, can be great controls on garden pests.

The Mexican Free-Tailed bat’s Circle of Life

The longest-lived Mexican Free-Tailed bat known lived for eight years. Because the bat has many predators including hawks, owls, kestrels, skunks, snakes, and raccoons the Free-Tailed bat’s numbers remain controlled.

Male bats vocalize and mark territories during breeding season to attract potential mates. Female Free-Tailed bats gather with their young in large roosts known as maternity or nursery roosts. A promiscuous species of bat, the Free-Tailed bat will mate with multiple partners. Female bats will give birth to one pup each year in the summer for approximately five years. Unlike some other species of bats, the young Free-Tailed bats roost separately from their mother in warmer parts of the roost. It is thought that the mother Free-Tailed bat recognizes her baby’s call among thousands of others in a roost, using it to locate the baby and care for and feed it. Between four and seven weeks the young Mexican Free-Tailed bat is weaned and independent.

Mexican Free-Tailed Bats and Humans

Although bats have a creepy-looking appearance and occasionally swoop down a little too close, most bat species are not hostile to humans, and prefer to stay away from them. If roosts are built in or around manmade structures they can become a pest, but they are also great predators of garden-devastating critters like aphids and beetles.

As it turns out, the Mexican Free-Tailed bat can actually produce a valuable resource:  its guano. Once harvested as a natural fertilizer, the guano in Free-Tailed bat caves is now treasured for its serious potential resources. Certain enzymes in the guano of a Free-Tailed bat are being studied for possible uses in production of natural pesticides, improving detergents, converting waste byproducts into alcohol, detoxifying industrial wastes, and even as a potential source of new antibiotics. But no one blames you if you don’t think washing your clothes or dishes with bat guano sounds appealing. Bat guano is also known to contain dangerous bacteria that can spread disease in animals and humans. Maybe a little more research on those guano antibiotics is a good idea.

Professional Mexican Free-Tailed bat Control

Professional control of the Mexican Free-Tailed bat is done using a combination of exclusion methods and should be employed if bats have actually entered a structure. An increase in chirping noises around dusk when bats leave their roosts to hunt could be an indication of bats roosting in your building. Control of these bats using measures to move their roosts elsewhere has been most effective. Professional exclusion of bats is most often accomplished in a series of steps, and can take a significant amount of time, depending on where the bats are in their mating and birthing seasons (all young bats must be weaned from their mothers for effective exclusion):

  1. Locate and seal entrance points:  Most professionals will observe potential roosting sites at night in order to identify openings that are allowing bats in and out. All primary entrances will be properly sealed, while some secondary openings will be left open to leave a way for all bats to vacate the roost.
  2. Get ‘em out:  After sealing most entry points, professionals employ certain methods known as “exclusion.” Eradicating bats from a property is done in the most humane manner possible, which combines sealing off entrance points with re-locating bats elsewhere. A bat valve or vent is placed over entrance points while the roost is out hunting for the night. This is a one-way valve that allows any bats left inside the roost to get out, but no bats can go back in to roost. Some pest companies will install a bat house on or near the premises to give the bats an alternative roosting location.
  3. The Dirty Work:  Any roosting sites of bats, especially in human-inhabited structures, must be thoroughly cleaned and sanitized once roosts are gone. The guano, urine, and other debris left behind by the bats is a health issue and must be removed immediately. If this sounds like a job you’d like to hire out, most companies will do the cleanup as well as exclusion.
  4. Granular Repellent is spread around entrances to keep bats from coming back to their roost. This is best employed in combination with the sealing of all openings and, as with all bat exclusion, only after young bats are weaned from their mothers.

DIY and Green Solutions for Mexican Free-Tailed Bat Control

Bat exclusion should really be done by a professional, but bat valves and sealing can be fairly easily done by anyone.

  1. One-Way Ticket:  Also used by professionals, a bat valve or cone is a one-way opening that is installed in the entry and exit points of a bat roost. This leaves an exit for the bat, but the valve is designed so that it cannot get back in. This should only be used after smaller alternate openings are identified and securely sealed. A bat valve or bat cone can be purchased at home improvement stores and installed by yourself.
  2. Netting: Use bird netting to cover any holes in your foundation or exterior walls. Leave at least one opening for the bat valve, then once all the bats are out, seal up the last hole with netting.
  3. Install a bat house:  Place a bat house away from your home in a cool, dark location. Consider placing food in the house to entice bats out of the roost in your home and in to the new house elsewhere. This should be done once entrances and exits are sealed and repellents or other exclusionary methods have been employed.

Mexican Free-Tailed bats are possibly the most abundant mammal in the Americas. For this reason, you are likely to come in contact with one in your lifetime. Although caves are the preferred roosting site for the Free-Tailed bat, they have also been known to set up shop in attics, bell towers, and inside ceilings and walls. Any sighting of a bat inside your structures should be taken care of right away, and any debris left behind cleaned up.