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Bat Nuisance Problems

Bat Fact Sheet

Big Brown BatThe presence of bats can be detected in several ways. At dusk, when bats leave roosts to feed, they may be seen exiting through eaves, vents or from behind shutters or siding. Noise from large colonies may also announce their presence. Droppings and dark brown stains may appear near eaves and beneath entrance holes and roosts. Bat droppings (guano) are easily crushed, revealing shiny bits of undigested insects. They are never white or chalky in appearance, as are the droppings of birds.

The 2 most common bats involved in nuisance complaints are the little brown bat and the big brown bat. The little brown bat ranges from 3.1 to 3.7 inches in length and has a wingspan of 8.6 to 10.5 inches. Big brown bats range from 4.1 to 4.8 inches in length, with a wingspan of 12.1 to 12.9 inches. Big brown bats can readily be distinguished from little brown bats in flight by their larger size, slow wingbeats and audible chatter.

A single bat that enters a home can often be removed easily. Closing off doorways to the room containing the bat and opening a window will usually prompt the bat to fly outside. A large jar or can may also be used to remove a bat. Move toward the bat slowly so that it is not startled and gently place the can over it. Slide stiff paper or cardboard under the can’s opening, using it as a lid when removing the bat. Heavy leather gloves should be used to remove a bat by hand. Bats, like all wild animals, may bite when handled and should not be removed bare-handed. Remember that bats, like other mammals, may be a source of rabies. The rabies virus is found in saliva and may be transmitted through the bite of an infected animal. If you are accidentally bitten while handling a bat, make sure the bat is saved for examination. Immediately wash the bite with soap and water and seek prompt medical advice. Non-bite exposures can also occur and should be treated in the same manner as a bite. A non-bite exposure occurs when saliva or brain tissue from an infected animal enters scratches, abrasions, open wounds, or mucous membranes (nose, mouth, eyes).

People usually know when they have been bitten by a bat. However, there are situations in which you should seek medical advice even in the absence of an obvious bite wound. For example, if you awaken and find a bat in your room, see a bat in the room of an unattended child, or see a bat near a mentally impaired or intoxicated person, seek professional advice from your local health department and save the bat for possible testing.  For further information about rabies and bats refer to the Centers for Disease Control and Prevention's website.

Most colonies of bats are small and often remain unnoticed for many years. Large colonies residing in an attic or wall may become a nuisance because of noise and unsightly guano accumulations. Eviction and exclusion of roosting bats are the only safe, permanent solutions to a nuisance problem. Numerous repellents and techniques may be used in an effort to evict nuisance bats.

Chemical Repellents: Aerosol dog and cat repellents are useful in limited situations, such as discouraging the use of a particular night roosting spot. They should never be applied while the bats are present. Direct contact is harmful to the bats and may cause them to fly at the "attacker" in their haste to get away.

Mechanical Repellents: Several mechanical repellents may help discourage bats. They are usually safer to humans than chemical repellents. Illumination of an attic or eaves with floodlights often discourages residence. Attics may also be cooled with fans to make the temperature unsuitable for roosting. Ultrasonic devices are seldom successful.

Exclusion and Bat-proofing

One of the simplest techniques for solving nuisance problems is letting the bats exit on their own and then preventing their re-entry to the roost. Little brown bats do not winter in buildings, so bat-proofing can be done after they travel to their winter roost site. Big brown bats usually travel to other roosts also, but they have been known to use building roosts in the winter. If nuisance problems involve big brown bats or if rapid exclusion is necessary, the first step is to find the exit(s) by watching the bats emerge at dusk. Stains from body oils or droppings may help pinpoint exits.

A simple one-way exclusion gate can be made using half-inch polypropylene structural-grade bird netting. During the day, hang the netting around the exits, using staples or duct tape. The netting should be attached several inches above the exits and extend at least 2 feet to either side and below the exit. The sides may be attached, but the bottom must hang free. As bats leave to feed, they will drop out of the roost unhindered. When they return, they will be unable to fly directly into the roost. These exclusion nets should be left in place for 3 or 4 nights to insure that no bats remain in the roost. After exclusion, the openings can be repaired when convenient. Caulk, fine screen, and oakum (petroleum-soaked rope) are all easy ways to seal openings. Exclusion should not be done from June through mid-August, as flightless young may be trapped and die in the roost, causing severe odor problems.

Another simple one-way excluder can be made from plastic strips. In a section of flexible plastic, cut small strips (about 1 inch wide) that will serve as tiny door flaps. The bats can push past them to exit, but the strips will not flex inward to allow re-entry. This excluder should be installed in the same manner as the bird netting.

Exclusion of bats from Spanish or concrete tile roofs is often as simple as installing a rain gutter. The gutters should be installed flush against the attachment surface. The upper edge of the gutter should be even with the lower edge of the tile, extending outward about 8 inches. This exclusion can be done any time, because the bats are still able to leave. Bats dislike climbing over the slippery metal gutter and usually will not return.

If you prefer to hire someone to exclude and bat-proof your home, it is best to seek a specialist. If the bats need to be trapped or handled, the specialist must be licensed by the DEEP Wildlife Division. As with any business dealing, it is advisable to get more than one estimate for the job. Beware of scare tactics, and remember:

  • Bats do not multiply like rabbits.
  • Even sick bats rarely attack people or pets.
  • Bats are not attracted in hordes by the scent of other bats.
  • Bats have very few parasites, so additional spraying for parasites is not necessary.
  • Permanent physical exclusion is essential for any bat control job.
  • The use of poisons to eliminate a bat colony is illegal without a special permit.
  • Bat guano is not "toxic."
  • Rabies rates in bat populations are not increasing.

Be careful when removing bat droppings from indoor roosts. Histoplasmosis, a fungal disease associated with the droppings of birds and bats, can result from the disturbance of dried droppings. Disturbance causes the fungal spores to become airborne, and spores entering the lungs can cause respiratory problems. However, histoplasmosis is seldom fatal; mild cases are common and often go unnoticed. Hot, dry attics rarely allow the spores to survive; thus, this disease is much more common in chicken roosts than in indoor bat roosts. Histoplasmosis is easily preventable--wearing a mask when removing accumulations of droppings prevents inhalation of the spores. logo

Do you need additional help and advice concerning nuisance wildlife? Check out and select "Connecticut" as your state to get started. is supported by the Northeast Association of Fish and Wildlife Agencies and the Northeast Wildlife Damage Management Cooperative.

Content last updated on April 1, 2020.