Bats: what you can and should do when found in homes and other structures

SALT LAKE CITY -- Bats are sometimes a problem, especially in older neighborhoods and rural agricultural areas where homes and outbuildings tend to be inviting to them. A misstep in the eviction process can increase your risk and those of your animals.

Bat exclusion, or sealing off entrance points, should never be attempted between mid-May and mid-September because the young bats will be trapped within the structure. Summer evictions are risky. Summer exclusions usually kill many bats and force the panicked bats to encounter building occupants, resulting in bites and rabies concerns. The best time to do a bat exclusion is late fall or even winter when it has been confirmed the bats have departed for hibernation and before they return.

There are no registered bat pesticides and using pesticides to kill them would be illegal. Their carcasses could attract attention from children, dogs, cats and people, and could cause an unfortunate visit to the doctor for rabies or rabies prevention.

Additionally, sometimes you hear of or see for sale ultrasonic pest-repelling devices. But, while manufacturers and vendors claim they work, there is no reliable evidence that they do. Here are some tips on solving a bat problem.

What to do if a bat enters your home

Once in a while, a bat may become disoriented and accidently enter your home through an open window or screen door. If this should happen, leave the doors or windows open and turn off the lights. When the bat becomes reoriented, it will detect the airflow and probably leave. If the lights are left on, it may seek a dark place within the house.

Never use a tennis racquet with the intent of killing a bat, because it seldom works. You will just injure it, and it is hazardous and inhumane. If the bat does not leave, the best approach is to catch it with a net, lidded coffee can or bucket or a gloved hand. Also keep in mind that once you catch it, you need to have a plan of what to do with it. A possibility would be to call a local zoo or university to check for interest in your catch.

If there are bats in a building and exclusion is planned, the health department should be advised and plans should be made to have them present when specific bats are captured to be tested for rabies. Sometimes, health officials opt not to attend the capture, usually because they are OK and confident when a professional licensed exterminator is doing the work. You should be aware that because of the complexity of bat control and the associated difficulty and danger, often it is beyond the scope of many pest control companies. Some companies will refer you to a wildlife control company to do the eviction.

But the health department should always be informed about what is planned and be encouraged to participate. It is not recommended to try to do this yourself. If the bats are identified as rabid, control should never be attempted without the supervision and oversight of local officials.

What to do if you find a dead bat?

If you find a dead bat lying on the ground, do not pick it up. Call the health department or pick it up with tongs, put in a bag and take it to the health department for testing. If you find your child or pet has brought home the creature, ask the health department or doctor for recommendations and call your veterinarian.

The experts' advice on doing bat exclusions

When conducting an inspection, there should be at least two inspectors present in the attic approximately on half hour before sunset and should probably wait until at least an hour after sunset. There should be at least two inspections, one during the day and another at night.

The daylight inspection should be to evaluate the size and scope of the problem and observe possible materials needed to exclude the bats. The night inspection is trickier. A flashlight or other lights should never be used, since this could cause bats to be confused resulting in them not leaving. The best tool the excluders will have is their limited vision and ears to identify exit points. Sometimes just plain, old observation works just as well if you are sensitive and observant.

Once the points of exit are identified, the exclusion work can begin, but only after the bats are completely evacuated. At the risk of being redundant, exclusion sometimes means a health department will order a summer eviction for public health-related reasons. If that happens, watch out. Summer evictions are extremely risky and increases exponentially the possibility of human and pet contact near the structure where the eviction is happening. Also, while you may evict them from one structure, there are risks the bats could just go to another nearby structure nearby, spreading the problem.

Plastic bird netting is the most viable product to accomplish stop-gap exclusion, but must be applied to the structure at night. All prep work can be done during the day. The netting can be applied to the entire roof and weighted with fishing weights to prevent structural damage from anything heavier. Measure and cut during the day and then apply at night after the evacuation. Other nearby homes should probably also be netted since the problem may just be shifted to another part of the surrounding area.

The only effective way to get rid of bats is bat exclusion. In other words, you must seal off the entrance points of the home or building so they cannot get back in. A 3/8-inch opening is sufficient for a bat to enter. The best materials for a permanent exclusion are 1/4-inch hardware cloth, sheet metal, plywood or aluminum flashing. For a temporary exclusion, plastic bird netting is good if properly applied. Or use soft cheesecloth or rags to stuff in the openings.

Bide your time when possible and avoid any disruption to the colony. Then in the fall, try again. A more permanent exclusion can be done in late fall. Winter is the best time as long as it is before the bats return.

Where do bats choose to live?

No one is sure exactly why bats chose to roost in a particular area, but evidence suggest they prefer areas near streams, ponds, lakes and rivers, and places with high temperatures during the day. Attics are particularly inviting. Additionally, if there has been a previous infestation, bats can detect the smell and re-colonize if a structure has not been bat-proofed. Bats do not gnaw, but they are experts at finding exposed areas like roof rafters, ceiling joists and brick voids.

Some people like the idea of using bats for insect control. Bat houses have become increasingly popular. Sometimes they are put up in hope of drawing them out or away from buildings. There are many factors that affect whether or not a bat will actually use the housing. The considerations are height off the ground, temperatures, how the sun and wind affect the house, and the bat house's construction. Unfortunately, many of the bat houses available at garden stores are poorly constructed and improperly designed. The best resource for bat house designs and management practices is in Texas, according to www.batcon.org.

The majority of bats that inhabit human structures are females and they do so to form a nursery or maternity colony. Bats give live birth. They have an unusual ability to mate and then store the fertile sperm until June and July when they birth offspring. Afterward, they usually stick around all summer, departing in September or October.

Bats overwinter in locations like caves, hollow trees, rock crevices and drainage pipes and big brown bats will sometimes overwinter in a heated building. They usually overwinter in small groups of one to six bats. They enter structures in the first warm days of spring, usually in April. In southern locations or when there are less harsh weather conditions, it can be earlier.

There are roughly 40 different species of bats in the United States and the specific species of bat is often difficult even for professional to identify. Bats eat large amounts of insects, like mosquitoes and other worrisome flying insects that are considered to be human disease vectors.

Mostly bats are harmless to humans and rarely attack unless provoked or they are sick with rabies. Most tropical fruit is pollinated by bats. Imagine no bananas! While the percentage of infected bats is small, they should always be viewed with caution and as potentially dangerous. Rabies can occur in bats with no symptoms.

Why remove bats?

There is good reason to remove bats if they inhabit a building or home. They scratch, squeak and create an unwelcome intrusion with all of their weird and creepy sounds. Additionally, when they defecate, their urine and droppings are odorous, can stain walls and ceilings, and attract a host of other insects.

The buildup of their dropping in attics and soil creates an environmental hazard. The droppings can create an ideal habitat for the growth of fungal organism that can produce a respiratory illness called histoplasmosis. The fungus spores may be drawn into the lungs when breathing in dust near affected areas. This illness, not only affects humans, but also animals.

The incidence of histoplasmosis is small in structural roosts, but several incidents occur yearly nationwide. Whenever someone decides to check or investigate a known roost, safety precautions should be taken, including wearing dust respirators, heavy leather gloves, coveralls and boots that will protect ankles and legs from exposure.

The three most common bat types are:

1. Big brown bat, about four inches in length, weighing in at one half ounce and with a wingspan of about 12-14 inches. They have a furry, brown coat with blackish ears.
2. Little brown bat, the second most common type, they are chocolate brown, weight about a one quarter ounce and have a wing span of about 9-10 inches.
3. Mexican free-tail bat, the third most common bat type is widely distributed through the country as far north as southern Oregon. They are also chocolate brown, about one half ounce in weight and have a wingspan of about 12-14 inches. They are most easily identified by their free tail that extends beyond their body.

Bats are among the most interesting creatures on earth. But there is culturally a creep factor. Unfortunately, bats are one of the most misunderstood creatures and one of the most beneficial at the same time.

References and resources include:

Frantz, S.C., “Batproofing structures with bird netting checkvalves” in Twelfth Vertebrae Pest Conference, University of California Davis, 1986.

Frishman, A.M., "The Vertebrae Pest Handbook," Advanstar Communications, Cleveland, Ohio.

Greenhall, A. M., "House Bat Mangement," U.S. Department of the Interior, Fish and Wildlife Service, resource publication 143, 1982.

“ Bats" in "Prevention and Control of Wildlife Damage," University of Nebraska Lincoln, 1994.

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