Throughout history, bats have aroused thecuriosity and interest of humans. Their abil-ity to fly, their secretiveness and their noc-

turnal habits undoubtedly have contributed tobat folklore, superstition and fear.

Most bats found in Texas live in caves andtrees. Many roost under bridges, in buildings orin other man-made structures. Roosts are usuallydark, secluded areas where the bats spend theday sleeping. Bats normally leave the roost tofeed just after sunset and feed off and onthroughout the night. Most bats return to theroost just before daylight.

The most common bat in urban areas is theMexican free-tailed bat (Tadarida brasiliensis).Although they occur in most parts of Texas,Mexican free-tailed bats are more heavily con-centrated in the southern half of the state.Mexican free-tailed bats form the largest coloniesof any mammal. Some Texas cave colonies con-tain as many as 20 million individuals, which col-lectively can consume more than 100 tons ofinsects nightly. Most Mexican free-tailed bats aremigratory. They spend the winter months inMexico and return to Texas in February orMarch.

Although bats can see, they fly by means ofan echo location system. By emitting high fre-quency sound waves, inaudible to humans andsimilar to sonar, flying bats are able to avoidobstacles and capture insects. Bats also emitaudible sounds that may be used for communi-cation.

L-19133-06

ControllingBATS

DamageIn urban areas, bats may become a nuisance

because of their squeaking, scratching and crawl-ing in attics, walls, chimneys or other structures.Their droppings and urine create an objection-able odor and, in some cases, can present ahealth threat. In addition, bats also can carryrabies. Although the incidence of rabies is lowcompared to the total population, the disease canbe transmitted very quickly within a colony.

Bat bites should always be considered aspotential rabies exposures and treated according-ly. Most bites occur when people or pets pick upsick or dying bats that have fallen to the ground.Normally, bats are not aggressive and rarelyattack people.

Biology and ReproductionMexican free-tailed batTotal length: 3 1⁄2 inches.Wingspan: 11 to 13 inches.Color: Brownish black above, grayish brown

below.Tail: Lower half of tail is free of connecting

membrane or “free-tailed.”Gestation period: 77 to 86 days.Litter size: One.Litter numbers: One per year usually born in

late spring or early summer.Weaning: 6 weeks.Life span: 10 years.

Control MethodsBefore an attempt is made to control bats, it is

essential to verify that bats are actually the causeof the nuisance. Twittering and rustling sounds inthe chimney may be caused by chimney swifts.Scratching or thumping sounds in the attic orwalls could indicate the presence of rats, squir-rels, raccoons or other animals. Bats may some-times be detected by the presence of a black-brown oily stain left by their body oils, and/or bythe presence of droppings around openings theyuse to enter or leave a structure.

Exclusion. The best way to discourage batsfrom roosting in houses or other buildings is toclose all openings through which they enter thestructure. Bats may enter buildings throughunprotected chimneys, louvers or vents, brokenwindows, eaves, loose flashing and other places.Bats can crawl through openings as narrow as3⁄8 inch, so you will need to inspect carefully tolocate all possible entrances.

Exclusion methods should be used for at least5 to 7 days before any bat proofing begins so thatbats have time to leave the structure. The besttime for bat proofing is in the fall after the batshave left for the winter. Because very young bats(pups) do not fly and remain in the roost areauntil they are older, any exclusion or repairsmade from May through August may trap thepups inside the structure.

One exclusion method is to hang plastic orlightweight netting over entrance holes. The net-ting should have about 1⁄6-inch squares (birdnet-ting) and be at least 2 feet wide. It should be hung1 to 4 inches in front of bat exit holes and extendat least 2 feet below the lowest exit point. Thiswill allow the bats to leave the structure but keepthem from finding their way back inside (see Fig.1). Use waterproof duct tape, staples, woodenlathe strips, or other suitable material to attachthe netting to the structure.

For smaller entry holes, use a tube of 2-inch-diameter PVC pipe to exclude bats. Exclusiontubes should be about 10 inches long. Squeezeone end of the tube so that it fits into the hole orcrevice, or cut the end of the tube into flaps thatcan be fit over the opening and stapled, nailed, ortaped to the inside wall of the building. Do not letthe tube project more than 1⁄4 inch into the open-

ing so that bats can easily enter the tube to exit.Bats are unable to cling to the smooth surface ofthe tube and will not be able to reenter. A pieceof lightweight cloth or plastic can be tapedaround the end of the tube that projects to theoutside to further reduce the likelihood of batsreentering, though this is usually not necessary.

After the exclusion period (5 to 7 days), coveropenings with sheet metal or 1⁄4 -inch hardwarecloth. Smaller openings and cracks can be sealedwith caulking, metal flashing, weather stripping,steel wool, insulation or other suitable material.

1” to 4”wood strip

Birdnetting

FFiigguurree 11.. Birdnetting will allow the bats to emerge butkeep them from finding their way back.

Unlike rodents, bats will not gnaw their waythrough wood or building materials and are easi-ly deterred once the openings are sealed. If anyentrances are overlooked, however, the bats willsoon find them; so it may be necessary to observethe building closely for several evenings to makesure all openings have been sealed.

Trapping. Although exclusion is the pre-ferred solution to bat problems, bats may betrapped alive before bat proofing is done. A vari-ety of traps, tunnel nets or plastic cylinders canbe used. These are usually placed over the build-ing entrance the bats are using. The bats are cap-tured when they try to leave the roost during thenight (see Fig. 2). Trapping bats should be left toa professional or to persons experienced withhandling bats.

Repellents. At present, naphthalene is theonly chemical registered as a repellent for bats.Naphthalene crystals or flakes can be placed inareas where bats are roosting. The disadvantageof using naphthalene is that it is effective only fora limited time. Once the odor dissipates, the batsmay return. Follow label instructions when usingany chemical.

Illumination also can be an effective repel-lent. Because bats prefer dark, secluded areas forroosting, floodlights strung throughout the atticor near the roosting site may cause them to leave.Illumination is cleaner and safer for both humansand bats than chemical repellents, but in somesituations using lights is difficult and costly.

It is believed that high frequency soundwaves (4,000 to 18,000 cycles per second) maydeter bats, perhaps by interfering with their abil-ity to navigate when flying. A variety of ultra-sonic devices are sold for this purpose, but theireffectiveness is questionable.

Toxicants. There are no toxicants registeredfor bat control.

Safety ConsiderationsFrequently, one or two bats may be found in

a house. They sometimes enter through the chim-ney, especially if the damper is left open. TheU.S. Centers for Disease Control and Preventionrecommends that if a bat is found in the room ofan unattended child or a person who is sleeping,intoxicated or mentally impaired, the person

should seek medical advice and the bat should betested for rabies. If there was no potential for aperson to have direct contact with the bat, it canbe removed by opening windows and outsidedoors. If the bat refuses to leave, it can be cap-tured in a net, small box, can, or heavily glovedhand and then released outside. Avoid touchingbats with bare hands. Although they are not usu-ally aggressive, they will bite if handled improp-erly.

RestrictionsMany species of bats are found in Texas and

some are protected by state law. Before conduct-ing any type of bat control or relocating any batsthat have been captured, contact local represen-tatives of the Texas Parks and WildlifeDepartment.

For additional information, contact the near-est office of Texas Cooperative Extension—Wildlife Services.

Entrance to roost

Clothfunnel

5-inch pipe

Garbage bag

FFiigguurree 22.. An effective bat trap can be made easily fromavailable materials.

Extension programs serve people of all ages regardless of socioeconomic level, race, color, sex, religion, disability, or national origin.Wildlife Services is a program of Texas Cooperative Extension cooperating with the United States Department of Agriculture—

Animal and Plant Health Inspection Service–Wildlife Services.

TCE—Wildlife ServicesP.O. Box 100410 • San Antonio, Texas 78201-1710

1M, Revision