Bat exclusion and control by the University of Florida IFAS

Bats In Buildings
W. H. Kern, Jr.

Bats are highly beneficial wild mammals. They are not flying rodents, but belong to a unique order of mammals called the Chiroptera (chiro= hand, ptera= wing). Bats are more closely related to primates (monkeys and humans) than they are to rodents. There are two families and 18 species of bats that breed in the eastern United States. Twenty-one species of bats have been found in Florida, but only thirteen species are known to breed in the state. Eight species are considered to be accidental introductions, including all the fruit and nectar bats (4 species). All of Florida's resident bats feed on night-flying insects. Each bat eats about its weight in food every night. This means that even a small colony, numbering several hundred individuals, consumes hundreds of pounds of insects every year. These insectivorous bats have tiny sharp teeth for chewing insects. Bats lack the chisel-like incisors of rodents thus, cannot use their teeth to gnaw wood or wires in structures

During the day bats rest in dark secluded roosts, such as caves, hollow trees, under bridges, crevices, and the attics of buildings. In winter when insects are scarce, some bats migrate like some birds do, while others hibernate in caves, trees, or buildings. Most bats in Florida enter torpor (a form of deep sleep) during the day and on winter nights when it is too cold for their insect food to fly. Most bat species only have one baby per year. So it takes bat populations a long time to recover from human acts of destruction. Bats are long-lived animals. The little brown bat from the northern states is known to live up to 35 years. Bats in Florida can probably live more than 10 to 12 years. Bats are creatures of habit and will frequent the same roost year after year, even if they only use it seasonally.

Bats are often feared as carriers of rabies. Bats can become infected with the rabies virus, as can dogs, cats, raccoons, and skunks. But unlike these animals, bats infected with rabies do not generally become deranged by the virus's damage to the brain and attack people or other animals. They usually become paralyzed and die quietly. The infection rate for house-dwelling bats is very low, ranging from 1 per 2000 (0.05%) in the southeastern bat to 4 per 1,130 (0.35%) in the Brazilian free-tailed bat. Not picking up bats found on the ground or other accessible location will reduce your chance of getting rabies from bats to virtually zero.

Bat Identification
A guide to the bats of Florida ( Figure 1 ) is included in this publication. Table 1 summarizes the natural history of Florida bats.

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Figure 1. Free-tailed bats have the tail extend beyond the tail membrane. The Brazilian free-tailed bat (left) and the velvety free-tailed bat (right). Identification is based on forearm length and facial features. Color is often too variable to rely upon.

Removing Single Bats from a Building
Despite their importance as insect predators, bats can be a nuisance when they choose to live in houses, buildings, or other structures used by people. Problems such as noise, smell, accumulations of feces (guano) and urine, staining and spotting of surfaces, attraction of other pests such as flies or cockroaches, and the general fear of these mammals by the public may require that they be excluded from a structure.
Single bats occasionally enter buildings accidentally. This usually occurs in the spring or fall, when bats move between winter roosts and maternity roosts, or in the late summer when young bats have just learned to fly. Young bats can become confused, get lost, and turn up inside buildings where they don't belong. In most cases, all that is required is that access for escape be provided by opening a door or window. In cases where that is not possible, as in most air conditioned buildings, a bat can be captured by covering the resting individual with an empty coffee can. Then gently slide a piece of cardboard or heavy paper between the container and the surface on which the bat is resting, trapping it inside ( Figure 2 ). Small groups of bats, numbering fewer than 10 individuals, can also be removed in this way. If a small bat is resting quietly, it may be possible to pick it up while wearing heavy leather gloves. Never touch a bat with bare hands, it will bite to defend itself, as would any wild animal. Do not try to catch a flying bat; this is almost impossible and usually results in injuring the animal. After the bat is captured, take it outside, away from children and pets and let it fly away or place it high on the side of a tree or wall to fly away on its own. A torpid (cold and sleepy) bat will need to "warm up" before it can fly, put it on the sunlit side of a tree to get warm.

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Figure 2. Capturing a single bat indoors with a coffee cane and piece of cardboard.

If anyone is bitten, cleanse the wound thoroughly with soap and water and call your county health department for information and instructions. Try to collect the bat so it can be tested for rabies. NEVER pick up a bat you find lying on the ground. Keep children and pets away from it and if necessary move it to an inaccessible spot with a shovel or similar implement. Call the county animal control office or a nuisance wildlife trapper to have the bat removed.

Confirming the Presence of Bats in a Building
The presence of a bat colony in a building is often confirmed by seeing bats emerge from various openings at dusk. Squeaking and rustling noises coming from ceilings and walls may indicate a bat colony is present. The sounds may also come from mice or flying squirrels. Chirping noises coming from chimneys are usually made by nesting chimney swifts, which are small insect-eating birds. An opening, which can be as narrow as 1/4 inch, with a dirty stain below it may be the exit hole for bats ( Figure 3 ). Stains come from urine, feces, and body oils that are deposited around the opening as bats enter or leave the roost. Droppings on sidewalks, ledges, patios, or underneath rafters in an attic or barn may indicate bats are present. Bat droppings, which are brown or black and resemble instant rice grains in size and shape, are composed entirely of insect parts. Mouse droppings are similar in size and shape but do not crumble between your fingers to reveal fragments of insect cuticle. Gecko droppings are similar to bat droppings but the pieces of insects are larger, less chewed up, and have small white caps of uric acid on one end. Cockroach droppings are usually smaller and have 6 flattened sides, making them hexagonal in cross section.

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Figure 3. Entrance to a bate colony is indicated by staining around the opening and droppings below the opening.

Bat Proofing
As with most nuisance animal situations, preventing a problem is much easier and cheaper than correcting one ( Figure 4 ). To prevent bats from establishing themselves in a building, all attic and soffit vents should be screened with 1/4-inch hardware cloth or screen. Good ventilation of attics discourages bats from roosting and also discourages infestations of large peridomestic cockroaches. Vent holes in Spanish tile roofs should be less than 3/4 inch, but 1/2 inch is preferable. Larger holes should be covered with screen that is held in place with silicon chalk. Gaps in siding, spaces under warped fascia boards, spaces between house and chimney, and loose flashing and moldings should be sealed to exclude bats and other invading household pests.

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Figure 4. Hole or crack under a rotted eave; open cellar hatch; chimney, between house and chimney; openings where pipes/wiring meet house; roted window sill/loose screen; under siding; under roofing/Spanish tile; ridge cap; fascia boards, flashing; vent; soffits; rafters and hollow walls.

Excluding a Bat Colony
When bats do become established in a building where they are not wanted, the best and most permanent solution is exclusion. This is accomplished by the following steps:

Observe the building at dusk from all angles on three or four successive evenings to identify the entrance and exit openings that the bats are using.

Seal and bat-proof all other openings that bats do not use, but might use in the future. Some species of bats can enter through a crack or crevice that is only 1/4 inch wide. Sealing materials can include caulking, wood, sheet metal, plaster, cement, 1/4 inch hardware cloth, or window screen.

Plan to do the exclusions in the spring or fall. Bat exclusion should only be performed beginning August 15 and being completed by April 14. Most Florida bats give birth in the May and June. Exclusions must not be attempted when baby bats are present, as they do not fly with their mothers until they are almost full grown. Baby bats trapped in the roost by an inappropriate exclusion will die of thirst or starvation (considered Animal Cruelty under Florida Statute 828.12.1) and create a serious odor, staining, and fly problem. In Florida, exclusions should not be attempted from April 15 through August 14. Wait until the young are flying to exclude the colony. Avoid exclusions during cold weather because bats usually do not fly when temperatures are below 45°F.

Exclude the unwanted bats by placing one-way devices on the colony's exit points. These devices can be as simple as a plastic "sleeve" ( Figure 5 ), 1 ¾ inch PVC pipe, or a used caulking tube. Once the bats exit through this, it collapses behind them or they can not climb or crawl on the smooth plastic. Bat netting works the same way ( Figure 6 ). The top of the netting is attached securely to a wall, beam, or other solid surface above the roost opening and extends over it (Figure 7). The bottom of the netting is not attached or only secured at spots along the bottom edge. The netting can be secured with duct tape, staples, Velcro tabs, or silicon rubber chalking (Figure 8). The bats exit the roost, crawl out the bottom of the netting, escape, but are not able to find the roost opening when they return from feeding, because the netting covers the hole. Professional bat exclusion specialists have developed a variety of exclusion devices for special situations. Colonies in large structures or in high dangerous places should be excluded by experienced professionals with specialized equipment. Returning bats may fly around the roost openings, but will disperse within a day or so.

Once excluded, a large bat colony may leave behind external parasites such as bat bugs, soft ticks, or mites. Most bat parasites are host specific and will not bite people. Once the bats have been excluded, the application of a desiccant or insecticide dust throughout the roosting site will kill parasites. This is a good precaution to prevent their spread while they look for other hosts. Bat guano dries to form a crumbly, powdery substance that can grow a fungus called Histoplasma capsulatum. Spores from this fungus become airborne when the guano is disturbed. Inhaled spores develop into a yeast-like infection in the lungs. This produces a systemic disease called histoplasmosis, the effects of which can range from flu-like symptoms (in most people) to serious lung abscesses and lesions resembling tuberculosis (in a minority of others). When working in an area where bat guano is in contact with the soil, wear protective clothing and a cartridge respirator (capable of filtering particals as small as 2 microns) to avoid breathing guano dust. Prior to removing accumulated guano, spray it with a 1:10 bleach and water solution to hold down the dust and kill the fungus. Histoplasma has been found in bat caves, but has never been found in an above ground bat roost in Florida. This includes attics and under tile roofs.

Permanently seal roost openings when you are sure all bats have left the roost. Leave the excluder in place for at least seven days in warm weather or up to two weeks in cool or cold weather.

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Figure 5. A bat exclusion device made with heavy plastic sheeting.

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Figure 6. Use of bat/bird netting to exclude bats from a structure.

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Figure 7. Bat netting.

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Figure 8. Bat netting.

Other Methods of Bat Exclusion
Bat traps are being advertised for dealing with bat colonies in buildings. These devices are not recommended for routine bat exclusions. There is no justification for trapping bats unless it is part of a scientific study or public health surveillance. Bat traps put unnecessary stress on the trapped animals and increase human exposure to the bats. The Florida Bat Working Group, an association of biologists that study bats and bat-related issues in Florida, considers bat traps to be unacceptable methods of bat control.
Bright lights or fans directed toward the ceiling can be used to discourage bats from roosting in large structures that are difficult to seal, such as warehouses, barns, or similar buildings. Fiberglass insulation also discourages bats from roosting; this is probably due to the irritating nature of this material. Ultrasonic sound emitters for control of bats are expensive ($20 to $70) and there is no scientific evidence to indicate that they actually work. The animals simply move into sound shadows to avoid the sound.

Bats and the Law
In Florida, all bats are classified as native non-game wildlife by the Florida Fish and Wildlife Conservation Commission and are protected by law from wanton destruction. Two species in Florida bats (the Indiana bat and the gray bat, both of which generally do not occur in buildings) are classified as endangered species by the U. S. Fish and Wildlife Service and the Florida Fish and Wildlife Conservation Commission. The Florida bonneted bat is currently listed as a Federally threatened subspecies, but will likely be revised to a Critically Endangered Species with the 2004 revision of its status as a distinct species, endemic only to South Florida.
Title 68A-4.001 (1) and (2) of the Florida Administrative Code (FAC) makes it illegal to apply gasoline or other toxic substance to an animals den to drive it out. Title 68A -12.009 (1) of the Florida Administrative Code (effective date July 1, 1992) states that nuisance or destructive wildlife may not be taken with a gun and light, steel traps, or poisons without a specific permit issued by the executive director of the FF&WCC. Since no poisons or fumigants are legal or registered for control of bats in Florida, the FF&WCC will not issue any permits to poison bats. Poisoning a bat colony exposes people, especially children, and pets to large numbers of dead and dying bats, thus increasing the chance of someone being bitten by picking up a sick animal. Exclusion is the only recommended permanent solution to an unwanted bat colony in a building and a nuisance wildlife trapper permit is recommended. Both a FF&WCC nuisance wildlife trappers permit and a Florida Department of Agriculture and Consumer Services - Certified Pest Control Operators License for General Household Pest Control is required to capture or kill bats if you are not the property owner. This is due to the definitions of pest control in Florida State Law 482 that covers the pest control industry in Florida.

Naphthalene repellents are the only registered materials for bat control in Florida. However, use of this substance is not a permanent solution. Naphthalene evaporates and as soon as this occurs, the bats will return unless roost openings have been sealed. There is also the odor and expense of placing several pounds of naphthalene in a building where people live. If people are sensitive to the odor of mothballs, avoid using naphthalene. If naphthalene is used buy a pest control professional to repel bats from a structure, a pest control operators license is required to use this registered repellent. Nuisance wildlife trappers may not use chemical repellents, unless they also have a pest control operators license.

Bat Houses
Since bats are beneficial, many people want to keep them in the neighborhood while excluding them from a building. This may be accomplished by putting up one or more commercially available bat houses. Figures 9 and 10 shows plans for a basic construction. Bats enter and exit the house from the bottom of the house, which has been left open. Bats will not leave a building to move into a bat house. But if a colony is excluded, bats may move into the closest new accommodations. A bat house should be placed high on the east side of a pole or building (10 to 15 ft.), as far in advance of the exclusion as possible. There should be no obstructions directly below the bat house to interfere with the entry or exit of bats. Additional plans for bat houses are available from:
http://www.batcon.org/bhra/economyhouse.html

http://www.floridabats.org/BatHousePlans.htm

Figure 9. Plans for a single chamber bat house.

Figure 10. Plans for building a triple chambered bat house.

Selected References
Harvey, M.J., J.S. Altenbach and T.L. Best. 1999. Bats of the United States. Arkansas Game & Fish Commission, 64 pp.
Timm, R.M. and H.H. Genoways. 2004. The Florida Bonneted Bat, Eumops floridanus (Chiroptera: Molossidae): Distribution, morphometrics, systematics, and ecology. J. Mammol. 85(5):852-865.

Whitaker, J.O., Jr. and W.J. Hamilton, Jr. 1998. Mammals of the Eastern United States, Third edition. Cornell University Press, Ithaca, NY. 583pp.

Footnotes
1. This document is Fact Sheet ENY-268, a series of the Entomology and Nematology Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Reviewed: March 1995. Revised: June 2005.
2. W. H. Kern, Jr., assistant professor, Department of Entomology and Nematology, Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, Ft. Lauderdale, FL 32611.

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U.S. Department of Agriculture, Cooperative Extension Service, University of Florida, IFAS, Florida A. & M. University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Larry Arrington, Dean.

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