Bat Damage Identification

Identification | Biology | Damage ID | Management | Handling

Presence of Bats

Most bat problems fall into 3 main categories: bats living in the structure, lone bat encounters inside the living space, and bats loitering or flying around the exterior of a structure. Bats commonly enter buildings through openings associated with the roof edge and valleys, eaves, apex of the gable, chimney, attic or roof vent, dormers, and siding.

Common entry points for bats. Image by PCWD.

Bats often roost on the outside of buildings, behind shutters, and where the siding and edge boards are not joined properly, lapped, or sealed. They occasionally roost on porches and patios, in garages, and behind shingles and roof gutters. Other openings may be found under loose-fitting doors, around windows, and gaps around conduits (wiring, plumbing, air conditioning) that pass through walls and utility vents.

Bats squeeze through narrow slits and cracks. To manage bats, focus on any gap measuring approximately ¼ x ¾ inches or any hole measuring 5/8 inch wide. Such openings must be considered potential entries for the smaller species, such as little brown bats. Smaller species can access an opening no wider than 3/8 inch, or the diameter of a US dime.

Discovery of rub makrs, bat guano (scat) and sightings of bats usually are sufficient to confirm the presence of bats.

Damage to Structures

Guano and urine may be visible, especially near large colonies. Fecal pellets indicate the presence of bats and are found on attic floors, in wall recesses, and outside the house. Fecal pellets along and inside walls may indicate the presence of mice, rats, or even roaches. New York’s house bats are insectivorous and their droppings are easily distinguished from those of small rodents. Droppings from bats tend to be segmented, elongated, and friable. When crushed, they become powdery and reveal shiny bits of undigested insect remains. In contrast, droppings from mice and rats tend to taper, are not segmented, are harder, and are more fibrous. Those rodent droppings do not become powdery when crushed (unless they are extremely aged).

Bat guano (whole, left; crushed, right) looks similar to mouse droppings except for the shiny speckles and susceptibility to crumble. Photo by UNL.

The droppings of some birds occasionally may be found along with those of bats. Bat droppings never contain the white chalky material characteristic of the feces of these other animals.

Bat excrement produces an unpleasant odor as it decomposes in attics, wall spaces, and other voids. The pungent, musty, acrid odor often can be detected from outside a building containing a large or long-term colony. Similar odor problems occur when animals die in inaccessible locations. The odor also attracts arthropods that may later invade other areas of a building. Bats urinate and defecate when exiting a roost, causing multiple spotting and staining on sides of buildings, windows, patio furniture, automobiles, and objects near entry and exit holes, or beneath roosts.

Bat droppings outside an attic vent. Photo by Stephen Vantasse.

Rub marks may occur on surfaces along walls, under loose woodwork, between bricks, and around other bat entryways. Rubs often have a smooth, polished appearance. The stained area is slightly sticky, may contain a few bat hairs, and is yellow-brown to blackish brown in color. The smooth gloss of the rub marks is due to oils from fur and other bodily secretions mixed with dust, deposited there as many animals pass repeatedly for a long period over the same surface. Openings marked in this way have been used repeatedly by bats.

Damage to Livestock and Pets

Bats that are infected with rabies can transmit the disease to pets and livestock during encounters. Though less than 0.1% of all bats have rabies, the percentages increase to less than 3% for bats that interact with people and animals.

Damage to Landscapes

Bats do not damage gardens or landscapes.

Health and Safety Concerns

Guano may provide a growth medium for microorganisms, some of which are pathogenic (e.g., histoplasmosis) to humans. Accumulations of guano may fill spaces between walls, floors, and ceilings. Guano may create a safety hazard on floors, steps, and ladders, and may even cause ceilings to collapse. Accumulations stain ceilings, soffits, and siding, producing unsightly and unsanitary conditions. The weight of droppings and urine can potentially compromise structures. Excrement may contaminate stored food, commercial products, and work surfaces.

Urine readily crystallizes at room temperature. In warm conditions, such as under roofs exposed to sun and on chimney walls, urine evaporates so quickly that it crystallizes in great accumulations. Boards and beams saturated with urine acquire a whitish powder-like coating. With large numbers of bats, thick and hard stalactites and stalagmites of crystallized bat urine occasionally form.

Although fresh urine from a single bat is relatively odorless, that of any moderate-sized colony is obvious. The odor increases during damp weather. Over a long period of time, urine may cause mild deterioration of wood. As urine saturates the surfaces of dry wood beams and crystallizes, the wood fibers expand and separate. The fibers then are torn loose by the bats crawling over such surfaces, resulting in wood fibers being mixed with guano accumulations underneath.

The proximity of bat roosts to human living quarters can result in excreta, animal dander, fragments of arthropods, and various microorganisms entering air ducts, as well as falling onto the unfortunate residents below. Such contaminants can result in airborne particles of public health significance.

Do not disturb deposits of guano unnecessarily. If possible, dampen with water or schedule outdoor work at a time when the ground is relatively wet to minimize airborne dust. To protect the environment, decontamination must be conducted in accordance with state and local regulations. Decontamination of an active bat roost should be conducted only after the bats have been excluded or after bats have departed for hibernation.

Arthropods (fungivores, detritivores, predators, and bat ectoparasites) often are associated with large or long-term bat colonies in buildings. The diversity depends on the number of bats, age and quantity of excreta deposits, and season. Arthropods, such as dermestid beetles (Attagenus megatoma), contribute to the decomposition of guano and insect remnants, but also may become a pest of stored goods and a nuisance within the living quarters. Cockroaches (e.g., Blatta orientalis) attracted to guano may invade other parts of a building. Bat bugs (Cimex spp.) are sometimes found crawling on the surface of beams or around holes leading to secluded recesses used by bats.

Bat bug (left) with bed bug (right). Photo by Jim Kalisch, UNL Entomology.

Ectoparasites (ticks, mites, fleas, and bugs) rarely attack humans or pets and quickly die in the absence of bats. Ectoparasites may become a nuisance, however, following exclusion of large numbers of bats from a well-established roost site.

Rabies in a bat colony can pass through generations. Estimates vary, but most agree that less than 1% of all bats carry rabies. Bats that are found on the ground and have exhibited unusual behaviors are more likely to carry rabies. Bite marks from bats are not always obvious on human skin.

It may be difficult to identify a bite from a bat. Photo by NE Health and Human Services.

A rabid bat transmits the disease by biting another mammal or transferring its bodily fluids to another mammal in any other manner. As the disease progresses, the bat becomes increasingly paralyzed and dies as a result of the infection. The virus in the carcass remains infectious until decomposition is well advanced. Therefore, every bite from or contact with a bat must be considered a potential exposure to rabies.

Aerial transmission of the rabies virus from bats to humans is not a known route of infection for humans entering bat roosts in buildings in temperate North America.

The potential for rabies exposure has occurred if anyone in the building:

  1. was awakened to find a bat flying in their room,
  2. found a bat in a room with an unattended child, whether sleeping or not, or
  3. found a bat in a room with someone who was unable to assess whether they were bitten by a bat.

If a possible exposure has taken place, try to capture the bat in a manner that does not damage the head. Keep the bat cool but not frozen and deliver it to your county health department for testing. Do not release the bat if there has been a potential rabies exposure to humans. In New York, NWCOs are required to immediately notify the local health department, and the local county or city animal control officer, of any incidents involving possible human exposure to rabies. In situations where the bat’s whereabouts are unknown, local health officials will consult with your client to determine if post-exposure treatment is recommended. The following discussion is general information on treating potential rabies exposures. Always consult health officials to ensure that the latest protocols are being used.

Treat bite wounds immediately and thoroughly with soap and water and irrigate the wound with a virucidal agent, such as povidone-iodine solution, when available. If the bat is captured, it should be transported to a testing laboratory as soon as possible, and if immediate testing can be arranged, post-exposure treatment may be delayed up to 24 hours until the test results are known. Post-exposure treatment must be urgently administered if the bat cannot be captured, if prompt delivery to the testing laboratory is not possible, if the specimen is not suitable for reliable diagnosis, if the victim’s immune system is compromised or suppressed, or if the test results prove positive for rabies. The prophylaxis (treatment) has little resemblance to that of many years ago. Today, it consists of 1 dose of rabies immune globulin (human origin) and 1 dose of rabies vaccine (human diploid cell) administered preferably on the day of the incident. Additional shots of the vaccine are usually administered 3, 7, and 14 days following the initial treatment. Newspapers, television, and other mass media sometimes misrepresent the risk of rabid bats to humans. However, the unfortunate average of one to two deaths per year in the US show the need to pay prompt attention to bat bites and other exposures.

Exposure to rabies can be prevented if people refrain from handling bats. People should be strongly cautioned never to touch bats with bare hands. All necessary measures should be taken to ensure that bats cannot enter living quarters in houses and apartments.

Pet cats and dogs should be regularly vaccinated for rabies. Valuable livestock also should be vaccinated if kept in buildings that harbor bats or are in a rabies outbreak area. While transmission of rabies from bats to terrestrial mammals apparently is not common, such incidents have been reported. Dogs, cats, and livestock that have been exposed to a rabid or suspected rabid animal, but are not currently vaccinated, must either be quarantined or destroyed as determined by local health officials.

Histoplasmosis is a common lung disease of worldwide distribution caused by a microscopic fungus, Histoplasma capsulatum. It is a saprophytic mold that grows in soil with high nitrogen content, generally associated with the guano and debris of birds (particularly starlings and chickens) and bats. Wind probably is the main agent of dispersal, but the fungus can survive and be transmitted from one site to another in the intestinal contents of bats and on the appendages of bats and birds. The disease can be acquired by the casual inhalation of windblown spores, but infection is more likely to result from a visit to a point-source of the fungus. Relative to bats, such sources include roosts in barns, attics, belfries, and soil enriched with guano.

Wild and domestic animals are susceptible to histoplasmosis, but bats are the most important animal vectors. Unlike bats, birds do not appear to become infected with the fungus. Both the presence of guano and particular environmental conditions are necessary for H. capsulatum to proliferate. In avian habitats, the fungus apparently grows best where the guano is in large deposits, rotting, and mixed with soil, rather than in nests or in fresh deposits. Specific requirements regarding bats have not been described, though bat roosts with long-term infestations are often mentioned in the literature.

When soil or guano containing H. capsulatum is physically disturbed, the spores become airborne. Perople at particular risk of histoplasmosis include cavers, bat biologists, pest control technicians, NWCOs, people who clean or work in areas where bats have habitually roosted, and people in contact with guano-enriched soil (e.g., the foundation of a building where guano has sifted down through the walls).

Infection occurs upon inhalation of spores and can result in a variety of clinical problems. Severity partially depends on the quantity of spores inhaled. The infection may remain localized in the lungs where it may resolve uneventfully. Such infections are identified only by the presence of a positive histoplasma skin test or calcified lesions on routine radiographs. Other individuals may have chronic or progressive lung disease requiring treatment. Less severe forms of these infections may be accompanied by fever, cough, and generalized symptoms similar to a prolonged influenza. Resolution of the disease confers a degree of immunity to reinfection and varying degrees of hypersensitivity to H. capsulatum. Massive reinfection in highly sensitized lungs may result in a fatal acute allergic reaction.

In a small percentage of chronic histoplasmosis cases, the fungus disseminates to involve multiple organ systems and may be fatal. This condition usually is found in young children (1 year or older) and in adults with compromised immune systems.

Bat roosts known or suspected to be contaminated with H. capsulatum should only be entered while wearing a protective mask certified by the National Institute for Occupational Safety and Health (NIOSH), capable of filtering out particles as small as 2 microns in diameter, or a self-contained breathing apparatus. In known contaminated areas, wear PPE that can be removed at the site and placed in a plastic bag for later decontamination with formalin and washing. Clean all footwear before leaving the site to prevent dissemination of spores in cars, the office, at home, and elsewhere. Actual control measures may not be necessary unless bat droppings become a problem or the risk of human contact is significant.

Nuisance Problems

Some people are frightened by the presence of bats flying around the outside of their house. Bats often fly around swimming pools, from which they drink or catch insects. White light with an ultraviolet component, commonly used for porch lights, building illumination, street and parking lot lights, may attract flying insects, which in turn attract bats. Just the sight of a bat outdoors is more than some homeowners can tolerate. Education is a good remedy for such situations.

Disturbing sounds may be heard from vocalizations, grooming, scratching, crawling, or climbing in attics, under eaves, behind walls, and between floors. Bats become particularly noisy on hot days in attics, before leaving the roost at dusk, and upon returning at dawn. However, rustling sounds in chimneys also may be caused by birds or raccoons. Scratching and thumping sounds in attics and behind walls may indicate rats, mice, or squirrels.