Bats

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Bats

Bats are the only mammals that actually fly (flying squirrels glide). They also have a highly developed echolocation system which allows them to capture flying insects at night. Bats catch insects in flight either with their mouth, wings, or tail membranes. They usually forage from about an hour after sunset to about an hour before sunrise, stopping to rest occasionally under open porches, eaves, trees or other overhanging structures.

Bats spend their days roosting in a semi-torpid state. Often bats choose to roost in the attic or walls of occupied dwellings, posing problems for property owners. Most colonies of bats go unnoticed, but they may become a nuisance due to their vocalization and activity, or odors and stains from urine, feces and rejected food. Many residents wish to eliminate these winged mammals because they can infect humans or pets with rabies. Only a small proportion (less than 1 percent) of Northeastern bats are rabid. Even if rabies is confirmed from one bat in a colony, most of the remaining animals will be healthy. Symptoms of rabid bats include erratic flight, activity during the daytime, and weakness or paralysis causing the bat to fall from its roost. Most human exposure to rabies occurs when people attempt to help grounded bats. If sick or dead bats are found, local public health agencies should be contacted immediately.

The big brown bat (Eptesicus fuscus), Eastern pipistrelle (Pipistrellus subflavus), and four species of little brown bats (Myotis spp.) are social bats. They usually form roost colonies during summer in attics, barns, caves or the walls of older buildings. A colony may consist of a few dozen up to several hundred individuals. In winter, these bats often roost in caves or abandoned mine shafts, but a few big brown bats may remain in attics.

Most species of bats in the Northeast mate promiscuously during fall. The young of social species are born in maternity colonies during late spring. Adult females have only one litter per year, and bear one to two young per litter. Body heat from the colony maintains warm temperatures for the young bats. Juveniles develop rapidly, and are usually able to fly in about three weeks. Bats have a relatively long life span, and may survive 10-20 years.

No pesticides are currently registered for lethal control of bats in the United States. Chemical controls may actually increase bat rabies risks by producing sick individuals, or by driving bats from attics into living areas. Application of pesticides may pose human health risks because fumes or powders move to occupied floors of the building.

What can homeowners do if bats decide to roost in their attics? The only long-term control method is to batproof the home or building in which a colony is roosting. All bats should be outside the building before the entrance points are sealed (implement control efforts at night). Batproofing should be attempted as soon as an unwanted colony is detected, except during early summer when young flightless individuals may be present. Trapped bats will soon die creating foul odors.

Main access points to structures are found by observing the animals leaving the building at dusk. Bats may enter an opening as small as 1/4 x 1-1/2 inches. Cracks or crevices can be sealed with caulking compound or oakum. Larger openings can be covered with metal flashing or 1/4-inch mesh hardware wire. One primary hole should be kept open until bats exit for the evening, then it can be temporarily closed with a wad of aluminum foil. Trapped animals will leave the following evening if the seal is removed at the normal exit time. After checking for remaining individuals, the opening can be permanently sealed. Bats will seek other entry points, so the building should be checked each evening for several days.

Colonies in horizontal moldings or behind shutters will be discouraged by removing the shutters or opening the molding so there are no dark recesses. Shutters can be reattached to the home with 1-2 inch wooden block spacers.

Installation of lighting in roost areas will also discourage bats (install wires properly to avoid fire hazards). The lights should be left on 24 hours a day for several weeks. Increasing ventilation to lower temperatures may cause bats to leave in some cases.

Mothballs (naphthalene or paradichlorobenzene) may repel colonies in confined areas with poor ventilation. Recommended application rates are usually high, and vapors could reach living areas posing a health hazard to humans. Ultrasonic devices have not effectively repelled bats.

To remove a single bat from an occupied room, turn the lights on and open the window. Usually the bat will leave on its own without handling. If this doesn't work, wait for the bat to land and cover it with a coffee can. Slide cardboard under the can, and release the bat outdoors if it has not contacted humans or pets.

Once bats are removed from a dwelling, any caked fecal material or crystallized urine should be removed from flooring or beams. The odor of bat excrement may act as a pheromone and attract other bats. The fungus Histoplasma capsulatum can be contracted by breathing spores in the dust of bat feces, so respirators and protective clothing should be worn while working in bat roosts. All contaminated insulation should also be discarded. Surfaces contaminated with urine or feces can be disinfected by spraying with a solution of 1 part bleach/20 parts tap water. Deodorants can then be applied to mask any remaining odors.

In summary, bats are beneficial because they eat large numbers of insects. Excluding bats from structures will be the most practical type of bat control.

Adapted from Paul D. Curtis, Department of Natural Resources, Cornell University, 2001

Pesticides are poisonous! Read and follow all safety precautions on labels. Handle carefully and store in original containers out of reach of children, pets or livestock. Dispose of empty containers immediately, in a safe manner and place. Pesticides should never be stored with foods or in areas where people eat.

When trade names are used for identification, no product endorsement is implied, nor is discrimination intended against similar materials. Be sure that the pesticide you intend to use is registered for the state of use.

The user of this information assumes all risk for personal injury or property damage.

For more information, call the URI CE Gardening and Food Safety Hotline at 1-800-448-1011 or (401)874-2929 from outside Rhode Island; Monday-Thursday between 9 am and 2 pm.

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