Getting Bats out of the Attic

Cathie Showalter wrote us from Burkina Faso asking “is there someone who could advise us on how to get rid of bats from our attic?” Bats are generally helpful to have around the yard of a home. Some bats can eat 150 to 600 flying insects per hour, including mosquitoes and moths (whose young are common garden pests) and perhaps some beneficial insects. However, they are NOT pleasant or healthy to have in the house. In Cathie’s case, the guano (bat manure) is sifting between the ceiling and the walls. Breathing the dust of bat or bird droppings can lead to a fungal disease called histoplasmosis, which has flu-like symptoms or worse. We know others of you likely face this problem, so here is what we have learned.

Cathie suggested that electronic, ultrasonic noise pest repellers might be of use. We called a catalog company and were told that the device would indeed work on bats. However, we also discovered that the Bat Conservation International (BCI) web site states emphatically that ultrasonic devices do NOT work. Bats may even be attracted to the ultrasonic sound, according to BCI!

Some other bat control methods may or may not be practical. The book Bugs, Slugs & Other Thugs: controlling garden pests organically states that if electricity is available, one could light the attic well and the bats would presumably leave. The book also mentions that recorded distress calls can keep bats away, but no further details were offered.

A former missionary in Kenya who had a similar experience with bats suggested that it would help to keep the guano swept up and put mothballs in the attic. BCI states that “to be at all effective, [mothballs] must evaporate rapidly, requiring frequent replacement.” They state that “aerosol dog and cat repellents may discourage bat use of a particular roosting spot for periods of up to several months. They have been used effectively to prevent bats from roosting above porches. The spray is applied by day when bats are not present. Aerosol repellents are not an adequate substitute for exclusion in the case of day roosts and never should be applied when bats are in a roost.” (We found one such product, “Boundary Dog and Cat Repellent” on the Internet at PetQuarters.com for $7.69 plus shipping. A local pet store sells a comparable product for $9.99).

In many cases, suspending 5 cm (2 in) wide by 18x25 cm (7- 10 in) long strips of aluminum foil or helium-filled Mylar balloons at a roost will deter bats.

BCI also described a method of bat exclusion that is safe for bats and humans. It involves hanging a lightweight polypropylene mesh over openings through which bats enter. The mesh should be 1/6-inch mesh size, or at most ¼-inch (0.42-0.64 cm). A sheet of heavyweight plastic can be used in place of the netting. The mesh or plastic should hang at least two feet below and to the sides of the entry point. It should be propped so that there is a one to two inch space between the exit/entry hole and the plastic. This allows the bats space to leave the hole, but prevents them from re-entering. In effect, it is a one-way valve for bats. The mesh or plastic should be left in place at least 2 or 3 days, to assure all the bats have left, and until the hole is closed.

It should be noted that if at all possible, this exclusion method should not be used during periods when there are flightless young bats in the roost. If you exclude the mother from the roost area, the young will die–a needless cruelty as well as a potential smelly mess!

For a permanent solution to the problem, after the bats have been excluded it is necessary to seal off all openings greater than ¼ inch with putty, screen or metal flashing. This is the step that is often difficult in homes with earth brick walls and metal sheeting roofs.

A final solution encountered seems promising. Once you have evicted the bats from your attic, build bat houses nearby so that they have an alternative place to roost. If you would like to build a bat house, either to attract evicted bats or attract bats to your yard, ECHO can send you simple plans about how to build a good bat house.