Bat Exclusion Defined
Popular “home remedies” for eliminating bats in the house are temporary, ineffective, and/or illegal. No pesticides are registered for bat control. Moth balls (naphthalene) can be temporarily effective, but don’t count on it. Moth balls are made to deter moths. Other types of repellents may not be registered for use as bat repellents and therefore cannot legally be used to harm or repel bats. Bright lights, as well as fans and air-conditioners, may be effective but temporary controls. In addition, ultrasonic and electromagnetic devices do not effectively repel bats, rodents or insect pests, despite advertising claims.
Exclusion remains the only effective way to prevent and control bats from entering a structure. Bats can be excluded by sealing exterior openings larger than ½-inch, using caulk, expandable foam, plywood, mortar, metal flashing, steel wool or ¼-inch mesh screen or netting. Make sure doors, windows and vents have screens and are securely framed; chimneys are capped; and gaps around utility lines are plugged.
Bats may leave their summer roosting places in September and October to migrate south where they will over-winter. Therefore, bat entry points in structures are best sealed during the months of September through April, when no bats are present.This should be determine by a professional as some bats prefer to hibernate in the structure. Proper exclusion at this time will prevent bats from entering the structure in spring. Only at certain times can exclusion be performed while bats are roosting within the structure. This involves sealing openings after the young bats are old enough to fly (Georgia Dept. of Natural Resources suggest August 15th or later).
More Exclusion Info
Special skills, equipment and training are required to identify all entry points and to apply exclusion materials to openings. Openings through which bats are entering and exiting a structure may be identified from inside the structure by entering the roosting area, an attic for example, on a sunny day when light can be seen through the openings.
Dark stains may be seen around and beneath openings used by bats. This results from bat guano and from “rub marks” where oils and dirt accumulate as bats pass through the openings. Yet another method of finding bat entry points is to watch for bats leaving the structure at dusk to make their evening feeding flights.
When all openings are identified, a “one-way valve” can be applied to each opening. One-way devices are those that allow bats to leave the structure, and prevent them from re-entering. This can be as simple as a sheet of plastic attached above the opening and allowed to hang flush against the building’s exterior. At dusk, the bats will find their way out beneath the plastic flap, but will not be able to lift the flap to re-enter the structure.
Similar devices can be constructed from screening or polypropylene netting of ¼-inch mesh, or a short length of PVC pipe can be positioned in the opening. Once all resident bats have exited the structure, the one-way devices can be removed and the openings immediately sealed as described above. Again, this type of exclusion should NOT be performed when young, flightless bats are present (typically May 1st-August 15th) unless they are causing health risks to humans living there.
Although exclusion is the best way to rid structures of bats, knowledge and timing are critical for effective “bat proofing.” Especially in older construction, there may be several bat entry points that can be difficult to discover.
If all openings are not found and sealed, bat problems will continue. Installing sealing materials and one-way devices can also be difficult because bat entry points are often several feet off the ground, requiring the use of ladders (note that falling is a much more common accident than being bitten by a rabid bat). For these reasons, bat exclusion may be best left to professionals.