Side Bar: Bat Houses and More Bat Facts
I had just entered a deep, restful sleep when a sharp elbow from my wife jolted me into a conscious but ornery state of alert. “There’s something in the attic!” she whispered. I strained my ears to catch the sound of an intruder while reaching for the flashlight I keep by the bed. After a few long minutes, I heard the noise that caused my wife such distress; a faint scratching resonated through the walls directly above the bed. As I lifted up the attic crawl door and swept the flashlight beam around the room, I suddenly was face to furry face with the intruders – a pair of brown bats.
Bats are a beneficial and generally gentle species, but they can become a nuisance if they decide to take up residence in your home or outbuildings. It is important, however, to understand the role that bats play in our environment and to shed some light on some of the common misconceptions people have about bats.
One of my earliest memories of bats involved watching them swoop and dip erratically at dusk in my hometown park. We were convinced at the time that they were divebombing us in order to get in our hair and give us rabies. What we didn’t know then was that the bats’ haphazard flight was their attempt to follow and eat insects that came out at night.
A great benefit provided by bats is their ability to consume enormous quantities of insects on their evening hunts. One Little Brown Bat can eat up to 1,000 mosquitoes in an hour. If you consider that even a small colony of bats may contain up to 50 or more members, it isn’t hard to imagine the positive role bats play in our ability to enjoy a bug-free summer night. Because of their aggressive efforts to catch and eat insects, bats often seem to fly erratically causing some people to believe they are being attacked by the bat. In truth, bats are excellent flyers and have no problem catching insects while avoiding people.
Bats have long been associated with rabies, but very few are ever infected with the disease. In fact, less than one half of one percent of bats carry rabies. According to Bat Conservation International (BCI), a non-profit organization dedicated to conservation, education and research involving bats, in more than 50 years only 14 people have contracted rabies from North American bat species. Unlike other animals, bats infected with rabies rarely become aggressive.
Bats truly are beneficial, but if you’re like me, you probably don’t want to hear them crawling around in your attic or have them roosting in your machine shed. However, there is a big difference between finding a stray bat flying around inside your house and having a colony in your home. Bat Conservation International says bats that fly into human living quarters are usually lost youngsters whose primary goal is safe escape. They often will leave on their own if a window or door to the outside is opened while others leading to the rest of the house are closed. Bats are not aggressive, even if chased, but may bite if grabbed. The BCI recommends using heavy leather gloves to handle a bat or trapping it under a coffee can and slipping a piece of cardboard underneath to cover the opening, then releasing it outside.
“The best defense is a good offense” may be a well-worn cliché, but when it comes to keeping bats out of buildings, the advice is well rewarded. The Minnesota Department of Natural Resources states on its website, “The only consistently successful method of excluding unwanted bats is permanent physical exclusion.” In other words, don’t give bats an opportunity to get inside in the first place.
According to the Minnesota DNR, timing is critical for excluding bats. Most bats will not hibernate in houses or outbuildings in climates with a distinct winter season because they require the cool constant temperature found in roosts such as caves, tunnels or mines. Late fall or very early spring is the best time to make your structure bat-proof because bats will have migrated to winter roosts.
To keep bats out of your living areas, you should cover chimneys and vents with half-inch hardware cloth screens. Also think about installing draft guards under doors and try to seal any other access point such as areas around screen doors, windows or plumbing. Bats won’t chew holes to gain access to your buildings, but they can squeeze through holes as small as 3/4 of an inch in diameter. Other typical entry points include louver fans, air intakes, exhaust vents, and openings for power and cable lines.
If you know bats are already in the building, you need to watch at dusk – when the bats emerge for their evening hunt – to find and mark their entry points. It is then possible to put up 1/2-inch structural grade bird or bat netting (available at garden or hardware stores), which acts as a one-way egress to allow bats to exit but not return. Drape the netting over each entry point extending several inches above, one foot to the sides and two feet below the openings. Attach the top and sides using tape, staples or Velcro. Leave the bottom open to allow the bats to crawl out, but they won’t be able to get back in the structure. After the bats have migrated in the fall, you should permanently block access points by using hardware cloth, caulk, weather-stripping, insulation materials, steel wool or even duct tape.
If there is a maternity colony in the structure (mothers and young), you need to wait until late summer to apply the exclusion bird netting. This will allow time to guarantee that the young bats are able to fly. If the netting is put in place too early, the young will be trapped inside causing them to starve to death and eventually create odor problems. Again, waiting until the bats have migrated may be the best option before you seal access points.
If you decide that you don’t feel comfortable removing bats yourself, most areas of the country have professionals willing to do the job for you. BCI has posted a list of reliable pest control operators on its website. Also, check with your local Department of Natural Resources and ask them if they keep lists of recommended pest control professionals.
In any case, don’t let the bats living around your place drive you batty – they are fun to watch, perform a valuable summertime service and really prefer to stay out of the house.
Tim Nephew is a freelance writer living in Northern Minnesota who manages his 80 acres for wildlife, saving a few acres for another of his passions, growing cold-climate-hardy grapes.