Celebrating Over 40 Years
"Safe Guarding What You Value Most"

Bats

Bats

Common names: Big brown bat / Little brown bat

Biology:

Little brown bat:

Pest status: Bats, generally beneficial because of their ravenous appetite for insects (including insect pests), are most often the victims of public ignorance. They have been the subject of myths, fables, and folklore for centuries. The blood-feeding habits of the vampire bat of Central and South America have contributed to many exaggerated tales on the American continent. Nevertheless, the fear of bats shared by a large segment of the public has possibly saved lives because rabies occurs in 4 to 6% of some bat populations. This instilled fear of bats has probably kept children, in particular, from being bitten. Picking up a live bat found on the ground may be tempting, but such bats are likely to be rabid. Several bat species have adapted readily to small openings in human-made structures, which they occupy as shelters. Bats can enter through openings as small as 3/8 inch in width. Common entry points to homes include gable vents, utility penetrations, loose flashing, uncapped chimney flues and fascia board gaps. The little brown bat and big brown bat are so adapted to buildings that during their maternity roosts almost always are associated with structures. When bats roost inside homes, particularly in attics, chimneys, or hollow spaces between walls and floors, the people who live there may object to noise from bat vocalizations or activity. Bat droppings (guano) and urine may cause a persistent stench that is insufferable to humans. Moisture from their urine and droppings can penetrate wallboard ceilings and walls and stain the interior surface. In some situations, the only remedy is to remove and replace the stained portion. If large colonies have roosted in a building for extended periods, guano removal can be painstaking, sometimes requiring that the siding be removed from the building for access. In food processing facilities and warehouses, human food may become contaminated by droppings from bats that inhabit buildings or from insects and arthropods that live in the guano deposits. Droppings are considered a food contamination by consumers, the Food and Drug Administration and USDA, and corrective measures must be taken. Bats are implicated in a number of human diseases, although paralytic rabies receives the greatest attention in public health. Histoplasmosis, an often fatal systemic fungal disease affecting humans, may be a significant hazard to people who work at removal of bats and bat guano (feces). The bats themselves do not transmit histoplasmosis, but the fungus, Histoplasma capsulatum, can be contracted by inhaling the airborne spores in the dust of bat manure that supports the growth of this fungus. Besides rabies and histoplasmosis, bats are also implicated in other diseases such as Chagas disease endemic relapsing fever, and St. Louis encephalitis. Bats carry ectoparasites, particularly the bat bug, Cimex pilosellus, which closely resembles the common bed bug. These may attack people when bats infest a house. Mites, ticks, and fleas, also listed among their parasites, may create minor health problems. Bat guano attracts flies, cockroaches, and other coprophagous (feces eating) insects. Whenever bats are controlled by exclusion or some other method, consideration must also be given to the simultaneous control of ectoparasites and other insects that may be left behind. The habits of bats may determine the type of control method used, so it is advantageous to know the species involved before control measures are undertaken. For example, it is important to know if the species forms large colonies, because the control approach could differ from that used on a species which roosts singly or in limited numbers (free-living bats). If the species migrates through an area and rarely stays any length of time, then control may not be justified, particularly if the bats roost outdoors, under eaves. For unfamiliar species that are not protected or endangered, a specimen should be collected (avoiding being bitten) for identification or classification by the local health department, college or university, or a biology teacher who has knowledge of bats. Once identified, that species’ habits, life history, etc. should be researched. Pest management professionals should become familiar with the identification and biology of the bat species in their area, particularly those that commonly use buildings as roosting sites.

CONTROL:

Harassment / Intimidation Electronic devices and light: Ultrasonic transmitter devices High frequency sound emission has been advocated by some sources to repel bats from premises; however, there is insufficient data at present to demonstrate efficacy. Most tests of such devices have been disappointing. Floodlights strung through an infested attic to illuminate all bat roosting sites may cause the bats to leave and seek a new location. Some authorities have found that populations of bat nurseries can be substantially reduced by bright artificial lighting in roosting sites. This method is believed most effective if done shortly after migratory bats arrive. In some situations, it is impossible to direct light to all possible roosting locations, such as in an attic, so the technique may not be effective in some types of structures. Conversely, white incandescent and mercury vapor lamps secured to the outside surfaces of buildings actually attract moths, beetles, mayflies and other insect prey sought after by bats, thereby encouraging bat activity nearby to such buildings.

Habitat Modification: If a bat is discovered indoors, a simple solution that allows the bat an opportunity to leave is to open the windows and doors. Lights indoors should be turned off or dimmed. Outdoor lights on buildings and residences should radiate yellow rather than white light. Yellow light attracts fewer night-flying insects which bats prey upon. Typical light bulbs and mercury vapor lamps are attractive to night-flying insects. Yellow “bug lights” and sodium vapor lamps are not attractive.

Physical / Mechanical Control

Exclusion: Exclusion is currently the recommended method of resolving most bat problems. A colony of bats or a few individuals of a solitary species may be excluded from a building through their removal and bat-proofing. Bat colonies are easier to dislodge from a roosting site if efforts are made soon after they initially take up residence. The longer a bat colony is permitted to exist at one location, the more difficult it may be to expel them from the building. Additionally, the colony may grow in size each year. Bats are most difficult to exclude from some large multistory buildings, such as warehouses and factories, that have many crevices and other places of concealment, and when semi-open roosting sites exist, such as large porches or roofs projecting over loading docks. Where ample habitat is found, a bat colony displaced from one area of a building may simply move to another area. If a seasonal infestation is tolerated for a time, the building manager may be relieved when the bats leave, believing the problem has disappeared. It is unwise, however, to assume that they will not return, because they frequently return year after year to the same site. One of the easiest times to bat-proof a building is after the bats have left for the season. To exclude most bat species from a building, openings larger than 3/8 inch must be closed to prevent access. Hardware cloth (1/4-inch mesh) or sheet metal are the materials used most often to close entrances, although softer building materials are also useful, such as aluminum flashing, particle board, and plywood. These materials can be fastened to the building using a heavy-duty staple gun or cordless screwdriver and wood screws. Unlike rodents, bats cannot gnaw their way through softer building materials, which are easier to work with and may more closely match the natural texture of the building. An effective way of sealing or filling voids within walls occupied by bats is to inject one of the newer types of wall insulation foams through holes bored into the wall. The work should be completed during the evening after the bats have left to feed. If foam or other loose-type insulation is used, be certain that any substantial amount of droppings are first removed and not just covered over, for objectionable odors may continue. Quick-setting hard putty can be used to close some small openings. Sealants, caulking compound, weather stripping or equivalent materials are effective for closing long, narrow cracks. Copper mesh or large stainless-steel scouring pads (which do not cause rust stains) are useful for temporarily plugging openings in Spanish tile roofs. Such openings can later be sealed with mortar When bat-proofing, the pest management professional should pay particular attention to chimneys, gable and soffit vents, cornices, warped siding and flashing, stone and brick veneer gaps, shake siding, fascia board gaps and utility penetrations.

Net curtain barriers: Where sanitation or public health reasons require that bats be eliminated immediately and bat-proofing is not readily achieved, netting over entire sides of buildings, from the roof line down, may be necessary until more effective measures can be completed.

Hand-removal: Hand collection is effective for removing the occasional bat from the living and work spaces in residences and commercial buildings; however, it is a labor-intensive approach to resolving a bat roosting problem and may also increase exposure of the trapper to rabid bats. An insect collecting net is a handy tool for collecting occasional bats that are flying about inside the living and work spaces of buildings.

Bat doors: Bat-proofing is difficult while a colony still infests a building and must be completed in two or more stages: Seal all bat entries except one or two of the principal openings; wait for several days, then make the final closures about one-half hour after dark, presumably when all bats are out of the building. Worker safety and the fear of high ladder work at night to close the last exit hole is sometimes a concern. A one-way door (bat door) device can purchased commercially (ready-built) or constructed that will permit the bats to escape during the evening but prevent them from reentering the roost. Where many exit holes exist, the same one-way passage of the bats can be accomplished by using light-weight plastic bird netting. The bats crawl out under the netting and are blocked by the netting when they attempt to reenter the opening to their roost. The returning bats that do not disperse to other areas may cluster or flounder about the plugged entry points. Such bats can be carefully collected, taking precautions to avoid bites, and disposed of properly. The building should be watched for several evenings at dusk to be sure the bats have not found an entry which may have been overlooked. The advantage to using exclusion devices or netting as a one-way door is that all of the work, including subsequent closing of entry points, can be completed during the daytime. Depending on species and time of year (particularly from early to mid-summer), there is always the possibility that some young may be present in the colony. They could be sealed in by bat-proofing and will subsequently die. Their carcasses may create odor and secondary pest problems. Several industrial deodorizing products are commercially available to help counter such odors, if retrieving the carcasses is impossible. These products may also help relieve the objectionable odor that remains from bat urine and guano even after the bats are gone and the accumulated guano has been removed. If possible, performing bat colony exclusion should be avoided during the period of maternity roosts and scheduled for later summer or fall.

CHEMICAL CONTROL

Repellents: Bats are, to a degree, repelled by the odor of naphthalene (crystals or flakes), the only EPA-registered repellent for indoor bat roosts. Naphthalene is potentially more effective in relatively confined air spaces, such as wall voids and poorly-ventilated attics and is much less effective in well-ventilated attics, soffits and barn lofts. Rottler does not recommend the use of these volatile compounds. Humans should avoid inhaling concentrated naphthalene (mothball) vapors as this compound is under suspicion by some state regulatory agencies of being a carcinogen.

Toxicants: No lethal pesticides are EPA-registered for bat control.