Donna Hensley
Why do some bats roost in buildings?
Buildings give bats protection from predators, stable temperatures and safe shelter to rest and raise their young. Bats have species-specific roost needs and preferences that vary by season, region, climate and activity. Some bat species use man-made structures like buildings and bridges to complement their selection of natural roosts. Other species must use buildings when natural roosts like caves and hollow trees are in decline or no longer available
Removing Bats Humanely
Bats are important in our natural world for many reasons. They’re vital pollinators, pest controllers and seed distributors – benefitting all of us. Quite frankly, if they’re in your space they’re likely to be just as scared and startled as you may be.
Removing a single bat or a colony of bats can be done safely and humanely. How you handle the removal is meaningful in protecting bat species, important in meeting legal protections… and greatly appreciated.
Note: Many bat species are federally protected – valued for their contributions to the eco-system and few in numbers. Mishandling or killing a federally protected species can result in stiff penalties. Check with your local wildlife agency for any state restrictions or guidelines before excluding a colony of bats.
What to do
If you’ve found a single bat or several roosting bats, one option is to call a specially trained bat rehabilitator or bat rescuer. Bat World Sanctuary provides a nationwide list of wildlife rehabilitators, biologists, veterinarians, conservationists and educators who have volunteered to help rescue and remove bats.
If a bat rehabilitator or rescuer is not available in your area, contact your state wildlife agency or Department of Natural Resources.
Donna Hensley
Handle with care
If you suspect a person or pet has been bitten or scratched by a bat, or you have found a bat in your home (especially in a child’s bedroom), immediately contact your county health department. Never directly handle bats.
Catch & release a single bat
A single bat in your house is rarely cause for alarm, and is usually just a lost or confused bat. In most cases, the “lost” bat will try to locate an exit and leave on its own. Assist the bat by opening windows and exterior doors, and closing any doors to adjacent rooms. Turn off lights and ceiling fans. Remain quiet and patient.
If the bat does not leave on its own and you can verify it has not come into contact with any one, you can safely capture the bat and release it outside by following the steps below.
Remove a colony of bats
In general, there are three things you should know about removing a colony of bats:
- Bats are wild animals and many species are protected under federal law.
- Removing a colony of bats is not easy but can be accomplished by following several steps.
- Hiring professional bat removers (often called bat excluders) is also a good option in removing a colony of bats.
Bat Colonies
Use tubes to remove bats
The goal of a successful exclusion is to provide controlled openings for bats to leave, without being able to get back in. Once the openings are in place for 7 warm nights, it is likely all the bats will have left and you can proceed with sealing the entry points.
In most cases, an ordinary tube – with a diameter of two inches (five centimeters) and about 10 inches (25.4 centimeters) in length – makes the best bat-removal device. Tubes can be made from PVC and flexible plastic tubing, purchased commercially, or can even be fashioned from empty caulking tubes.(*)
Tubes provide safe passage for bats when affixed to exits and entrances. Flexible, plastic tubes let you squeeze one end so it fits into a crevice. Tubes also allow you to cut one end of a tube into flaps which can be caulked, stapled, nailed or screwed over a bat exit or entrance. Tubes can be used on buildings with rough exterior walls, brick or stone houses and log cabins. Tubes also work best for holes at corners where walls meet and on horizontal surfaces such as soffits.
Tubes should project no more than one-quarter inch (six millimeters) into the opening to ensure that exiting bats can easily enter the tube from the inside of the structure.
Once the tube has been secured over the hole, a piece of lightweight, clear plastic can be taped around the tube’s outside end (see diagram) to further reduce the likelihood of bats reentering, though this is usually not necessary.
After the tube has been secured into or over an opening used by bats, any spaces between the outer rim of the tube and the building must be sealed shut. Also be sure to seal any other openings in the building that bats could use.
Leave the tube in place for a minimum of seven days to ensure all bats have left. After the bats have exited, the tube should be removed and the opening permanently sealed with water-based silicone caulking, hardware cloth or heavy-duty plastic mesh. In some cases, sealing may require repair or replacement of old, deteriorated wood.
When bats are using multiple openings to enter and exit, exclusion devices should be placed at each opening. If the bats do not appear to be exiting or seem to be having trouble doing so, add new tubes as needed.
(*) Empty caulking tubes can be used after the caps at both ends have been cut away. Caulking tubes must be thoroughly cleaned before they can be used for bat removals (exclusions) because dried caulk forms a rough surface that could allow bats to reenter.
Important notes
- Many states regulate bat exclusions. Check with your local wildlife agency for any restrictions on timing or methods of bat exclusion.
- Do not exclude bats during the pup-rearing season (April – September in North America). Wait until the fall or winter when all bat pups are volant and the colony has moved to winter habitat or hibernacula.
- Never simply wait for bats to fly out at night and then seal openings. Not all bats leave at the same time. Some may remain inside all night, especially during storms.
Caution! - Do NOT use products or structural modifications that block natural ventilation, like hanging plastic sheeting, over active roost exits and entrances.
- Do NOT use silicone, polyurethane or similar non-water-based caulk products.
- Do NOT use flexible netting or one-way doors, which can entangle bats and cause permanent injury or death.
- Do NOT use duct tape. Duct tape and similar adhesive tapes fail when surfaces are rough, coated with dust, mold and mildew, or when used in high humidity locations. Use of duct tape can result in re-entry or entrapment.
- Do NOT use expandable foam which can block ventilation and break down in the heat, allowing bats to re-enter. Expandable foam can kill bats that are exposed to the material before it dries. Dead bats have been found entombed in foam.
Hiring a pro to help you?
Safely and permanently removing bats from buildings requires knowledge, patience and attention to detail. It can involve working high on ladders, scaffolding and from a hydraulic lift. When hiring a professional, Bat Conservation International recommends finding an individual or company who meets the following criteria:
- Has prior verifiable bat removal experience (or at a minimum completed the NWCOA bat removal training course)
- Demonstrates familiarity with bat species to be excluded, such as roosting preferences, behavior and seasonal activity including maternity and nursing seasons
- Has a license for bat removal
- Is insured for any incidental damage that may occur during excusion
- Provides at least three client references (with phone numbers) for similar work
- Provides a written contract.
- Guarantees workmanship/materials for at least two years
Beware of an individual or company that:
- Uses scare tactics to convince you and your family that you’re in danger and must act immediately.
- Uses ultrasonic repellents for exclusion. These methods have not been scientifically proved effective – in fact, one study actually found that ultrasonic repellents may actually attract bats!
- Uses degradable materials like expandable foam, rags, paper and steel wool to close holes.
- Uses chemical pesticides to kill or repel bats – this is illegal in the U.S. and most European countries.
- Agrees to or advocates for the removal of bats during the maternity season.
Some bats sleep in buildings during the day.
Bats can enter buildings through holes and crevices as small as 1/2 inch.
Steps to prevent bats from entering buildings
Bats found in interior (living or working) spaces are usually there by accident and a single bat flying inside does not necessarily indicate that a colony is in residence. Occasionally a bat may fly through an open door or window, or be carried in by a pet. These accidental visitations can be prevented by keeping doors and windows screened, chimneys capped, and exterior basement or attic doors closed and in good repair.
Bats that roost in buildings are usually in structural voids, the spaces between the exterior and interior envelopes of a building.
Bats enter voids through openings on the exterior of buildings. A colony may remain unnoticed unless someone sees, hears or smells them. When a resident colony is present in the structure, lost bats may find their way into the living area once or twice a year. These events are usually rare, but may occur during the summer maternity season (lost juveniles), or when they awaken briefly from winter hibernation.
Prevention
Where bats can enter
Potential access areas for bats include structural penetrations as small as 5/16” (8mm) x 1½” (38 mm), or holes 5/8” (16mm) x 7/8” (22 mm), which can include expansion joints, holes, cracks or crevices on the exterior of a structure. As a general rule, if you can get your pinky finger in, a bat can enter. Most bat species choose roost entries in high, out-of-the-way areas (above 10 feet), but in some cases, bats will enter basements, cellars and other areas beneath a house.
Small bat colonies can usually be tolerated and simply left alone, but bats should always be prevented from entering human living quarters.
The first step in exclusions is to inspect the building’s interior for small openings through which bats could enter. All openings connecting the attic or other potential roosting areas to living quarters should be sealed, while entry points on the outside of the building are left open. Caulking, flashing, screening or insulation can be used to seal most openings on the inside. Draft guards should be placed beneath doors to attics; electrical and plumbing holes should be filled with steel wool, caulking or weather stripping.
Caulking, flashing, screening or heavy-duty mesh can be used to bat-proof most openings on the outside. Expanding foam or similar products should never be used to seal cracks in a building where bats are active because they can become caught in it. Caulking should be water-based and applied early enough in the day so it has time to dry before bats emerge in the evening.
Preventing bat access into the living space
Interior access can be prevented without disturbing the colony by closing interior openings such as those around plumbing or gas pipes, electrical wiring, or heating and air conditioning units found in utility closets, cabinets, behind appliances, and under sinks. Ensuring an interior “bat-free zone” will prevent the stress (for bat and human) of the sudden appearance of a flying bat in the home or workplace, and allows any further exclusion actions to be carefully considered and planned.
Although interior openings can be closed to prevent bat access to the living space, closing exterior penetrations can be fatal to roosting bats and should never be done without a solid plan to prevent entrapment.
Because entrapment occurs inside walls and other areas that are away from human view, exclusion attempts (or any event that prevents bats from leaving a building) can cause significant mortality that is rarely documentedand often unnoticed, making it nearly impossible to accurately quantify. Evidence of entrapment may include numerous bats suddenly appearing in the living space of a building. If recognized and acted upon quickly, bat mortality may be avoided. Signs that trapped bats have died of dehydration and starvation include strong putrid odors, and dark stains on interior walls or ceilings caused by seepage from decomposing bats.
How do bats get in?
Missing or Broken Chimney Caps
Torn Screens on Gable Vents
Where Masonry meets Siding or Cornice
Under Window Sills
Dormer Soffit / Roof Junction
Under Loose Shingles
Behind Downspouts & Gutters
Basement Doors
Torn Window Screens
Broken Siding
Eaves / Soffit Vents
Bats are legally protected
Legal protection of bats varies widely around the globe. In the U.K. and most European countries, all bat species and their roosts are protected – including bats who have roosted in buildings – by domestic and international legislation. In North America, bats have protections in their natural environments and some laws protect bats when they occupy a home or building. However, several species of conservation concern such as little brown bats and Florida bonneted bats might be found in man-made structures.
Be sure to check with your local wildlife agency about restrictions on timing or method of removal.