Bats are an interesting and valuable component of our environment. A few species (Table 1) frequently roost in buildings. While tolerable under some circumstances, the presence of bat roosts in close proximity to humans is often undesirable. Biologically (and often legally), the only long-term control technique is bat exclusion.
Physical contact with bats should be avoided. Potentially rabid bats pose a significant health threat to humans. School sites which regularly encounter bats on the premises should have an on-going student/staff/faculty education program to reduce potential for contact.
Individuals involved in bat management should be trained in basic bat biology, health concerns related to bats, and identifying signs of bat activity. Many states have laws requiring personnel involved with management projects to have a wildlife handler‘s permit or license. Pest situations involve incidental bats in human living space, bat roosts in buildings, and concerns with diseases like rabies and histoplasmosis.
Bat species most likely to be encountered in pest situations in school environments.
|Common and species name||Geographic distribution|
|Big brown bat, Eptesicus fuscus||Throughout the US.|
|Little brown bat, Myotis lucifugus||Throughout the US.|
|Mexican free-tailed bat, Tadarida brasiliensis||Roughly the southern half of the US.|
|Evening bat, Nycticeius humeralis||Eastern half of US north to southern Great Lakes.|
|Pallid bat, Antrozous palidus||Southwestern US and west coast.|
|Yuma myotis, Myotis yumanensis||Most of western third of US.|
Inspections should be done to determine bat entry points, the degree of structural modification needed to exclude bats, ways to prevent bats from entering human living space, and whether any person or pet has had direct contact with bats.
Bats normally enter near the top of structures. Unlike rodents, bats are not generally capable of chewing openings and must use existing holes. An opening ¼-inch by 1½-inch is sufficient for a small bat to squeeze through, but buildings with well-established roosts will probably have larger openings. Watching bats leave the roost at dusk can assist in locating the entry sites.
During an initial inspection, it should be ascertained whether any person or pet has been bitten, or otherwise had direct contact with a bat. If this has occurred, the local health department should be contacted.
Buildings vary on the degree of structural modification needed to successfully seal bat entry points. Often, spot repairs with simple materials will be sufficient. In some cases, part of the structure (such as the roof) may need to be rebuilt. In still other situations, as with many barns, total exclusion is not a practical approach.
Measures can be taken to prevent bats from entering the human living space of a building. Any opening to the walls or roof can provide access to bats. Common sites include gaps under and over attic doors, gaps around pipes passing into the ceiling, pocket doors which slide into the walls, loose fitting baseboards, and broken plaster. Either temporary (towel under attic door, steel wool in wall hole, etc.) or permanent steps can be taken to close these openings. Bats may also enter basements and other rooms through chimneys. The dampers should be kept closed on fireplaces when not in use, and chimney covers can help.
Bat exclusion on the exterior of a building is greatly facilitated with the use of checkvalves. These devices function as a one-way door for bats. When installed over the major entry sites, checkvalves allow bats to leave but not reenter the structure.
Somewhat controversial (and illegal in at least one state), bat traps are devices that, unlike checkvalves, do not allow one-way passage of bats but capture and hold the animals as they exit the entry site. The bats are generally either transported and released or destroyed. Individual bats can also be captured on sticky traps designed for rodents.
Some work has been done with combining exclusion with the use of bat houses as an alternative roosting site.
Increasing ventilation and illumination of attics and crawl spaces is sometimes done to try and reduce the environmental conditions attractive to roosting bats.
Although widely marketed to the public, ultrasonic devices purporting to repel bats have not been shown in independent testing to be effective.
Commonly used products for physical, cultural or mechanical management of bats and uses.
|one-way exclusion checkvalves||netting, screen, Batcone™||Installed over openings bats use to enter and leave structures such that exit is allowed and reentry is not.|
|exclusion||sealant, hardware cloth, wood||Permanently seals openings after all bats have exited the structure.|
|disrupt the calm||ceiling fan, mylar balloons||Bats will not roost in disturbed areas, position fan to move balloons in problem roosting areas for several days|
|slick surface||Cover substrate where bats are roosting with a smooth surface; bats will roost elsewhere.|
There are very few options in this category. A few products containing naphathalene (same ingredient as moth balls) are labeled for repelling bats. Napthalene-containing products should not be used due to human health hazards; naphthalene is one of the pesticides most frequently implicated in human pesticide poisonings.
Products containing polybutenes, that form an adhesive surface that are meant to repel pigeons and other birds, have been used around bat entry sites. However, since bats usually are not listed as target pests, this is an off-label use and thus prohibited in some states.
Until 1991, some states allowed the use of the anticoagulant chlorophacinone tracking powder (RoZol) for lethal control of bats. This is no longer the case, and there are currently no pesticides that may be legally used to kill bats.
Arizona Cooperative Extension. 2007. All About Bats. Pest Press. cals.arizona.edu/urbanipm/pest_press/2007/oct_nov.pdf (PDF)
Bat Conservation International. www.batcon.org
Curtis, P.D., J. Shultz, L. A. Braband, L. Berchielli and G. Batchelor. 2004. Best Practices for Nuisance Wildlife Control Operators; A Training Manual. NYS Department of Environmental Conservation and Cornell Cooperative Extension. nwco.net
Hygnstrom, S.E., R.M. Timm and G.E. Larson, eds. 1994. Prevention and Control of Wildlife Damage. University of Nebraska-Lincoln. 2 vols. digitalcommons.unl.edu/icwdmhandbook/
Internet Center for Wildlife Damage Management www.icwdm.org
Link, R. 2004. Living with Wildlife in the Pacific Northwest. Washington Department of Fish and Wildlife. 392 pp.
Salmon, T.P., D.A. Whisson and R.E. Marsh. 2006. Wildlife Pest Control Around Gardens and Homes. University of California. 122 pp.
Tuttle, M.D. 1988. America’s Neighborhood Bats; Understanding and Learning to Live in Harmony with Them. University of Texas Press. 95 pp.