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Bats are the only true flying mammals. There are many species
in Washington and all of them are beneficial insect eaters, consuming
literally tons of harmful insects each night. The most common
species to move into houses is the Little Brown Bat (Myotis
lucifugus). These small animals are about 3-1/2 inches long
with an 8 inch wingspread. Their colors range from yellow-brown
to dark brown.
Little Brown Bats roost in groups and are drawn to hot attics and wall voids in the spring and summer to bear their young (one per female) from about June-August. In the fall, most of these bats fly to winter hibernation roosts in caves or old mine shafts.
Health Hazards
Bats should not be regarded as dangerous. However, about one bat in a thousand MAY have rabies which eventually kills them. Little Brown Bats cannot easily transmit this disease to humans or pets due to their small teeth but problems can arise from trying to touch or pick up a sick bat. Unprovoked attacks are extremely rare.
If bitten by a bat or if infectious material (such as saliva) from a bat gets into your eyes, nose, mouth, or a wound -- wash the affected area thoroughly and get medical advice immediately. If a bat is found in a room with a sleeping person, capture it without damaging the head and place it in a container (See the CDC page on "Bats and Rabies" for more information and correct procedures). Dead bats should be kept under refrigeration until tested. Contact your local Health District as soon as possible. To avoid this disease, simply avoid touching bats, be sure your house is bat-proof (at least the living area) and be sure your pets are vaccinated. Call your veterinarian for vaccination information.
Histoplasmosis is another hazard in some states (not Washington). This airborne disease may be carried in bird and bat droppings. Few people exposed to this fungal disease become seriously ill but there is a potential risk of infection to any one removing or disturbing old, dusty bird or bat guano.
Contact your local health department or the Center for Disease Control for further information regarding these diseases.
House Bat Management
Bat colonies do not ordinarily cause structural damage to a building. However, very large colonies can, in time, drop enough urine and feces to cause an odor problem or even to seep through the floor or wall. In addition, bats can be disturbingly noisy as they squeak and scratch in the ceiling or wall voids.
The best way to solve a structural bat problem is to install one-way bat doors. Bat Conservation International. web site shows how this is done using various home-made exclusion devices. This should be done before June or after August to reduce the possibility of trapping young, flightless bats inside. Openings are usually easy to find by watching the house at dusk to see where the bats are coming out. Openings may be as narrow as 3/8 inch and there may be several. After several days, when the bats are all out, openings may be closed up. Expanding-foam products or caulking can be used.
Bats Need Friends Too
With the destruction of valuable habitat throughout the country, it's no wonder that bats take up residence in houses. If you want to give these beneficial flying wonders a place to live other than your attic, you can build a bat house for them (WDFW also has plans on line). Visit the B.C.I. home page and "Bats Northwest" for further information.
Sources:
America's Neighborhood Bats, Tuttle
House Bat Management, Resource Pub. 143. Greenhall
Natural History of Oregon Coast Mammals, General Technical Report
PNW133. Maser, Mate, Franklin and Dyrness
Urban Entomology, Ebling
For more information, please contact your local WSU Extension Office.
