Before beginning, though, homeowners must accept that bat exclusion can be a big job, particularly if you have a fairly dilapidated home, because there are so many cracks the bats can enter. However, if your house is structurally sound, and has only one or two bat entry points, it’s a pretty simple process to do yourself, according to Barbara French.
It’s best to plan bat exclusion in late summer or early spring because come mid-May, female bats begin giving birth to pups that cannot fly for several weeks.
If you start eviction too early in the summer, you may be left with orphaned baby bats in your home, which couldn’t survive. In much of the country, house bats migrate in the fall to hibernate in mines and deep caves. If your bats have left for their winter quarters and you know where they are coming in, late fall is an excellent time to seal up the all exterior entry points and clean out the droppings.
Not all bats migrate, however, especially in the Southeast. And sometimes, they will hibernate in the house itself. You cannot evict the bats in the winter if they are still present, because they will not be able fly out while still in hibernation.
Note the brown marks on the wall behind this bat exclusion netting.
A Bat Exclusion in Action
To see bat exclusion in practice, I decided to accompany Brian Reichman, a licensed Pennsylvania wildlife control specialist, on one of his projects. Each state has a wildlife or conservation department that can offer advice on how to find a licensed wildlife removal specialist. (This is not an exterminator; bats’ endangered status makes it illegal for exterminators to touch them).
We met at the home of the late Clarence James in Hawley, Pennsylvania. Clarence was the township historian and local square dance caller who had recently died at the age of 103. His son, Don, recalled how the house was known to harbor bats for at least 50 years, but Clarence didn’t care. He had also not done any major repair work on the house for decades, so the colony had swelled to more than 400 little brown bats.
When I arrived at the property, beneath part of the cornice I could see an exclusionary device, a flap of nylon netting attached to the building over a bat entry point. Excluders should be attached securely along their top and three quarters of the way down their sides with duct tape or staples, allow the netting to hang somewhat loosely and extend about 2 feet below the bat access point.
Placed over a bat entry point, such devices act as a one-way door. The bats crawl down and out the bottom of the netting to fly away, but when they return they fly straight to the opening and can’t figure out how to get back in.
Exclusionary devices are easy to make using nylon window screen with a mesh of 1/6 or smaller. Another option Barbara French recommends is to cover the openings with cleaned-out caulking tubes—ends cut off and pointed downwards. Bats can drop down and out through the tubes, but can’t climb back up the smooth surface. These excluders fit nicely into the curves on tile roofs.
In order to be effective, excluders must be placed over each bat entry point and left in place for at least a week, at which point the bats have given up trying to get back in, moving to a new home. Because the devices on Clarence James’ house had been up for more than a week, Brian was in the process of sealing all holes, cracks, and crevices with caulk or metal mesh to prevent their return. I asked him where the bats had gone. “Probably to the neighbors,” Brian shot back cheerfully. “Once a house bat, always a house bat!”
Cleaning Up the Guano
When the bats are gone, it’s time to clean up their mess. Bats have a keen sense of smell, and can sniff out the hint of a prior roosting spot from miles away, so all droppings must be carefully removed. Bat manure, or
guano, while apparently an excellent fertilizer, can contain a fungus called Histoplasma capsulatum.
Proper precautions are necessary when cleaning guano. This crew wears suits and masks, and uses a HEPA vacuum.
Inhaling the fungal spores can sometimes cause a respiratory infection in humans, so proper precautions are necessary for any cleanup. I donned some old clothes and a mask that Brian gave me with a filter capable of filtering out particles as small as 2 microns in diameter (the size of small fungal spores) and went upstairs. Heavy work gloves are also recommended.
The smell was overpowering, even through the mask. Belinda, Brian’s wife, assisted him and confessed, “The first time I did this, I told him, ‘I must really love you.”
Because this house had hundreds of bats living there for decades, it was a particularly big job that required a lot of cleanup. First Brian and Belinda tore off the dilapidated interior walls and ceiling, stained and smelling of bat urine, in order to expose the beams and supports. Then they vacuumed up the guano on the floor, walls, beams and even the ceiling-anywhere the bats had left their mark— using a professional HEPA utility vacuum. It’s a good idea to mist the guano with water first to help prevent the dust from getting into the air.
Finally, Brian sealed the windows, shut the door, sprayed the room with a commercial odor eliminator and antibacterial, and closed the room off for several hours until the spray dried. If you have a fairly small and accessible space, an alternative is to scrub all surfaces with a solution of 1 cup of bleach per gallon of water.
It’s important to clean diligently and make sure all openings have been sealed, because any remaining odor will tell bats the house is a great hotel, and they will move right back in. With the bats out, access points sealed, and the place scrubbed, Brian’s work was done and the problem solved.
Living With Bats
Not everyone blessed with bats decides to get rid of them. After all, bats are rarely dangerous-only about one half of one percent of all bats have rabies. Suppose you don’t hate bats; you just don’t want to share your house with them. In that case, before evicting them, you might consider putting up a bat house or two at some corner of your property. That way, when the bats are unable to get back into your house, they’ll have the bat house as an option. The bats will have their house, you’ll have yours, and you can be neighbors. Think of all the bugs they’ll eat!
Using Bat Boxes
One of the consequences of a successful bat eviction is that all those of displaced bats—the ones once sheltered in your rafters—will need a new place to live. Installing a bat box on your property makes it easy for them to find one.
Bat boxes installed on your property can lure the newly excluded–and evicted–bats to a new home.
Bat boxes can come in many shapes and sizes, but all have one thing in common: They are designed to provide cozy quarters for a colony of bats. From the outside, a bat house often looks like a boxy birdhouse on steroids—with one difference, entrance holes are at the bottom. Nonetheless, they can be adorned with clever detailing—we even discovered a bat box with Folk Victorian styling.
Inside, all feature several crevices so bats can roost in layers. Installing a bat box in the corner of your yard gives newly excluded critters a place to go, while keeping them close enough to provide major insect control on your property. With a single bat chomping down about 3,000 bugs a night, that’s a lot of pest protection for your al fresco dining.
Learn more about bat removal: