Information on Bats & Bat Damage
General Biology of Bats
Bats are the only mammals that truly fly, and they are not members of the rodent family. Bat species that live in groups are called colonial bats and species that live alone are referred to as solitary bats.
In Michigan, the common species that are encountered by humans are the big brown bats (Eptesicus fuscus) and the little brown bats (Myotus lucifugus). The little brown bat often forms maternity colonies in buildings during spring and summer; colonies with as many as 2000 bats have been documented. The big brown bats form much smaller colonies, typically ranging from 12-200 bats. Pregnant females of each species will congregate in colonies in mines, caves, buildings and other dark secluded spaces. In Michigan the bats give birth May through June, with both common species producing one young. Young bats grow quickly and are able to fly within about three weeks. Both species of bats live approximately 6-7 years, and often until age 10. There have been a few documentations of little brown bats living over 30 years.
Bats found in Michigan are insectivores. Some of the bats found here can consume up to one half of their body weight in insects in one night. It is a popular misconception that mosquitoes are a main stay in a bats diet, however they do prey on many other harmful insects.
Bat Damage and Damage Identification of Bats
Large numbers of bats living on walls, attics and other living spaces can be both a general nuisance and a possible health risk. Accumulating guano (bat droppings) can damage building materials and become very odiferous. The urea in bat guano has also been known to destroy paint, even the kinds used on vehicles.
Sometimes bats will appear inside homes, which for many people is a very frightening ordeal. Many of these bats found inside the living quarters are young bats that make a “wrong turn”, coming through an open window or door or an unscreened fireplace, and wind up inside instead of outdoors.
Health Hazards of Bats
Rabies is the most important health risk associated with bats. You will usually know if you have been bitten by a bat. However, bats have very small teeth and may leave marks that are not easily identifiable. The Center for Disease Control (CDC) advises that you seek medical advice if you awaken and find a bat in your room, or in the room of an unattended child, or if you see a bat near an intoxicated or mentally impaired person.
If you are bitten by a bat, or bodily fluids from a bat gets into your mouth, eyes, nose, or a wound, wash the affected area thoroughly with soap and water and get medical attention immediately. If possible the bat should be captured and sent to a laboratory for rabies testing. The good news is that less than 1% of the bat population is rabid. The bad news is that 5% of the bats that have been tested in the state of Michigan have tested positive for rabies.
Histoplasmosis is an airborne disease caused by a fungal organism that has been found in bat guano. Histoplasmosis primarly affects a person’s lungs, and its symptoms vary greatly. Chronic lung disease due to histoplasmosis resembles tuberculosis and can worsen over time. Special anti-fungal medications are needed to treat this disease. Occular histoplasmosis is another condition that affects the vision. Without proper treatment this can lead to impaired vision and sometimes even blindness.
Bat Damage Control Methods
Excluding bats from buildings using one-way devices in conjunction with sealing all potential entry points 1/4” x ½” and bigger, has proven to be the most effective long term solution. A close inspection of the colonized building must be the first step in a successful exclusion. After determining what areas need to be repaired or filled, the seal-up work is conducted, leaving key entry points open so a one-way net or exclusion device can be installed. This exclusion process should not be conducted when the young are flightless (usually this is June and July in Northern Michigan); doing this would result in starving the young and potential odor problems. In some instances the bats in northern Michigan will leave these roosts, sometime in the fall, permitting exclusion during their winter absence.
Many people have tried alternative solutions, but none are more effective than those methods mentioned above. Repellents and ultrasonic devices have shown no real effectiveness in deterring bat colonization. Scientific and public health literature have documented poisons to be ineffective and pose possible health hazards to people. There is no pesticide labeled for use on bats, therefore it is illegal to use this technique.