October 3, 2009
Solving Problems with Bats
Bats perform important ecological services and won't get tangled in your hair
The HSUS
Occasionally, a bat will accidently find herself inside a home, flying around and landing on curtains or furniture. Whether there by accident or to raise young, you can help bats out—that is, out of your house—humanely.
A bat or two may surprise you hanging from a porch ceiling, under the eaves, or in a carport. They are simply resting between feeding flights close to their food, insects attracted by outdoor lights. Bats flying at dusk above the yard are absolutely no cause for alarm. This is perfectly natural—the bats are foraging for flying insects.
Common problems and solutions- Bat colonies roosting in attics, chimneys, and crawl spaces
- Bat check valves
- Bats loose in buildings—accidental intruders
- Protection and conservation
- White Nose Syndrome
- Is that bat rabid?
Resources
Common conflicts and solutions
Bats are willing to use our attics, chimneys, and crawl spaces that offer warm temperatures they need to raise young. But their droppings can build up in long-used roosts. And from these colonies, bats occasionally find their way inside our living space.
Bats in houses can go unnoticed for years. When discovered, the homeowners often feel they have an immediate crisis, when, in fact, they have been living with the bats for years. This discovery should not lead to hasty reactions. Bats can be evicted humanely with minimal stress to both people and bats. Some bats migrate to winter roosts, making it even easier to do exclusion when they are not there.
Bat colonies roosting in attics, chimneys, and crawl spaces
Bats don't make holes to get into buildings; they use entry points we leave open. Small openings or narrow gaps high on houses admit bats. Bats may also enter under loose-fitting doors, around windows, and through gaps around conduits and utility vents.
Successfully evicting bats can be challenging. A knowledgeable professional who understands bat behavior and laws protecting bats may be your best option. Bat Conservation International's (BCI) website lists professionals who evict bats humanely. You state wildlife agency may also be a resource to find help.
If you try to do it yourself, your goal is to allow the bats to leave on their own but keep them from returning. Do this only when no dependent young are present—not from May through August. Many states specifically prohibit excluding bats when they are raising young.
Before even considering eviction, check with your state wildlife agency to make sure you know what laws must be followed, as well as to get a specific idea of when it is safe to exclude bats in your area.
For most migrating species in the northeast bats leave colonies for winter hibernation sites by the first week of September, but some species (big brown bats being a good example) will hibernate in buildings during the winter. So, early autumn is the best time to evict bats. If you find hibernating bats during the winter, wait until spring when the bats will be able to fend for themselves.
Here's a quick overview of how to evict bats.
- Find all outside entrances but do not simply seal up all openings at night. Not all the bats leave at the same time, or even all every night, and you will likely trap some bats inside.
- Install one-way bat check valves on all entrances you find. Check valves allow bats to leave but not return.
- Leave check valves in place for at least 5 to 7 days.
- Check carefully to be sure there are no bats left. Watch the outside of the house in the evening to make sure the bats have not found another way in.
- After you are sure the bats are gone, remove the check valves, and seal the entrances.
Before you try this at home, we recommend you carefully review the more detailed DIY advice on BCI's website.
Bat check valves
The concept of the bat check valve was developed by Stephen Frantz of the New York Department of Health and others more than thirty years ago. Elegantly simple, the check valve is merely a length of fiberglass bug screen, which you can easily obtain at any hardware store, which is cut and draped over the opening bats use to enter and exit the building. Upon exiting, the bats drop down to the open end of the check value at its bottom. When they return, they don't go to that opening but rather attempt to enter at the original entry point they are accustomed to. The check valve prevents that reentry.
Again, in the northeast work to exclude bats is done any time after September 1, with the check valves left up for at least a week to ensure all bats have been evicted. Many homeowners who recognize the value of having bats at work for insect control will opt to put up a bat house at the time of eviction, hoping the bats will find and use it, or occupy it on return the next spring,
Bats loose in buildings—accidental intruders
An individual bat may accidently intrude in a home. The bat may be first seen flying around a room early in the evening, landing on curtains or furniture and then taking flight again.
Remain calm and keep pets and children away. The bat will have to fly in a U-shaped path, gaining altitude near the walls and losing altitude in the center of the room so keep near a wall. Close interior doors and give the bat a way to get outside.
Important: Never try to handle a bat with your bare hands. Wear thick leather or similar work gloves—not cotton. A frightened bat can easily bite through cotton.
If the bat doesn't exit on his own, he probably landed somewhere he can hang—behind curtains or upholstered furniture, on hanging clothes, or in house plants. Try to capture him in a net, such as a butterfly net. Or, carefully place a plastic tub, study cardboard box, or similar container over him. Gently work a piece of cardboard or stiff paper under the container, trapping the bat inside.
A thick towel is a good way to capture a bat on the floor. Roll the bat up gently.
Important: If there is a possibility that a bat has bitten someone The Centers For Disease Control (CDC) recommend the bat be tested for rabies.
Take the bat outside away from bystanders and pets and let him go right away. Some bats can take off from the ground, but many can't. Leaving him near a tree trunk or other vertical surface is a good idea.
Next, find how he got in. The bat may have been roosting somewhere in the house and accidently found a route to the living space. Common entry points include gaps and openings that lead to attics or cellars—places that may harbor more bats. Inspect thoroughly and seal potential interior entrances.
Protection and conservation
Bats' public image turned from highly negative to mostly positive in recent times. Individuals and organizations raised awareness of the bat's ecological role and countered myths of their potential harm. Bats are a clear case where individuals made a very real difference for animal welfare.
For bat conservation, and because it is something of a fad, many people put up bat houses. Bats are fussy about temperature and other conditions. So, design, placement, and other factors strongly influence whether or not bats use a house. If you must exclude bats from a building, consider putting up well-designed and appropriately mounted bat houses first.
White Nose Syndrome
Since 2006, White Nose Syndrome has been devastating colonies of hibernating bats. First discovered near Albany, New York, it spread from Vermont to southern Virginia by 2009. In some colonies, 90 to 100 percent of bats are dying.
In all likelihood, this disease will continue to spread and continue to kill many bats. More than half the bat species in the United States, all those that hibernate, are at serious risk. These include four federally endangered species and 13 species of concern.
White Nose Syndrome is named for a white fungus on bats noses, ears, and wings. The exact workings of the disease are still not clear. It may indirectly cause death by continually disturbing them during hibernation. This uses up critical fat reserves too quickly and bats simply starve before springs brings abundant insects.
While people don't get sick from it, they may spread the White Nose fungus. Authorities have closed many caves to recreational visits. After visiting open caves, cavers should carefully decontaminate all clothes and gear. For the bats' sake, please don't enter closed caves and fully follow decontamination instructions if you enter open caves.
Is that bat rabid?
If you find a bat on the ground outside, she may be ill, temporarily stunned from flying into a window, or—if the weather is colder—she may be too cold and unable fly.
Bats generally aren’t aggressive and don’t bite without provocation, although any bat may bite in self-defense. If handled most bats will bite or try to bite defending themselves.
Never handle a bat barehanded! If you decide to contain the bat, use sturdy gloves and put the bat in a non-metallic (because of heat transfer) container that allows air to enter. Call your local animal control agency or a wildlife rehabilitator for assistance.
Public health and bats
Two infrequently encountered bat species are associated with a strain of rabies that has caused human deaths. The incidence of this disease in bat populations is extremely low.
Rabid bats generally aren't aggressive or bite without provocation. Most of the extremely rare instances when a bat exposed someone to rabies happened when the person accidently or carelessly handled a bat. Note: Be especially careful not to pick up a bat or take a bat from a pet's mouth with bare hands.
The National Centers for Disease Control and Prevention recommends people capture, if possible, any bat found in a room with a sleeping person. Give the bat to health authorities for rabies testing, which means she will be killed. CDC recommends this precaution because they suspect that adults may overlook and children may under-report the bites of tiny bat teeth.
Important: In any situation of potential rabies exposure, immediately consult your physician and local health authorities.
Large accumulations of bat droppings may encourage histoplasmosis fungus to grow. This fungus is common in the eastern and central US. As many as 80 percent of people tested in these areas prove to have already been exposed without knowing. People diagnosed with this disease typically work where bird or bat droppings accumulated (poultry farmers, contractors clearing old buildings) or explore caves where bats lived rather than merely live near bats.
Resources
» Purchase a copy of Wild Neighbors in our shop.
» If you are located within the D.C. Metro Area, take advantage of our wildlife conflict resolution service. Learn More