Figure 1. Big brown bat (Eptesicus fuscus). Photo by NYSDEC.
- List signs that indicate bats may be present.
- Communicate to clients the process for evicting and excluding bats from their home.
- List 3 scenarios that lead to the assumption that a client has been bitten and the bat must be tested for rabies.
Legal Status in New York
The lethal control of bats, even when there is a proven potential danger to humans, is often subject to careful scrutiny and interagency coordination. In New York, it is legal to kill bats found inside an occupied home, including endangered or threatened species, if necessary for rabies testing ordered by the health department. The non-lethal approaches in this document are not only preferred, but also the most effective. Lethal means are generally only desired when there has been a possible rabies exposure.
Some bat species are protected as either federally or state-listed endangered species. Become familiar with the appropriate federal and state laws before starting any nuisance management activities. A permit is usually required to harass, collect, harm, or kill a listed species. However, listed bats can be evicted from buildings without penalty. The Indiana bat (Myotis sodalis), northern long-eared bat (Myotis septentrionalis), and eastern small-footed bat (Myotis leibii), which are all protected in New York, can be confused for the little brown bat (Myotis lucifugus). Accurate identification is difficult, so the safest approach is to follow the guidance regarding the timing of the exclusion process.
Overview of Damage Prevention and Control Methods
- Change to exterior light bulbs less attractive to insects
- Use lights and fans to make roosting sites unattractive to bats
- One-way doors, check-valves, caulk, flashing, screening
- Not effective
Repellents and Toxicants
In New York, a NWCO must have a pesticide applicator license to use a repellent or toxicant.
- Naphthalene flakes are registered as a repellent
- No toxicants are registered
- Not practical
- Bat traps; prevent unnecessary stress or death to the bats
Conservation and Public Education
Despite the ecological value of bats, many people have an appropriate level of concern regarding these animals. While customers have the right to live in a home that is free of bats, it is important not to reinforce misinformation about bats. Many people worry about contracting rabies from bats, though in reality only a very small percentage of bats actually have the disease. Bat conservation is even more important now with white-nose syndrome threatening populations of bats.
White-nose syndrome (WNS) is a fungal infection that affects the exposed skin of a bat’s nose, ears, wings, and tail during the hibernation period. It may appear as a white growth on an infected bat’s nose or skin, or may not be visible. WNS has occurred simultaneously with massive die-offs in hibernating bat colonies in the eastern US. It appears that the fungus caused the deaths, but many unknowns still surround the disease. No evidence is available that suggests the white-nose fungus can infect humans. Research continues on WNS as biologists hope to stem massive die-offs of bats. WNS is extremely harmful to wintering colonial bats. Many caves are closed due to the occurrence of WNS or the potential for contamination. Strict equipment decontamination protocols are strongly recommended (see Whitenosesyndrome.org for current decontamination protocols).
Bats belong to the order Chiroptera and are the only mammals that can truly fly. The ability to fly, along with their elusiveness and nocturnal habits have contributed to bat folklore, superstition, and fear. More than 1,300 species are distributed worldwide, second in number only to Rodentia (rodents) among mammals. Among the 47 species of bats found north of Mexico, only a few cause problems for humans (vampire bats are not found in the US or Canada). Bats that congregate in colonies are called colonial bats; those that do not are solitary bats.
The species most often encountered in and around buildings in New York are the colonial big brown bats (Eptesicus fuscus, Figure 1) and little brown bats (Myotis lucifugus). Little brown bats were formerly the most common bats found in NY buildings. However, white-nose syndrome has decimated populations and it’s much less likely you’ll encounter this species now.
New York’s three listed bat species, the endangered Indiana bat (Myotis sodalis), the threatened northern long-eared bat (Myotis septentrionalis) and the species of special concern- the eastern small-footed bat (Myotis leibi), are also known to roost occasionally in buildings. Small-footed bats might turn up anywhere. The areas of New York State where Indiana and northern long-eared bats are most likely to be observed roosting in buildings are shown in Figure 2.
Solitary bats typically roost in tree foliage or under bark but occasionally are found in buildings, usually as transients during migration. These include eastern red bats (Lasiurus borealis), silver-haired bats (Lasionycteris noctivagans), and hoary bats (Lasiurus cinereus). Tri-colored bats (Perimyotis subflavus) also are solitary bats, but are year-round residents of New York and spend their winters in hibernation sites. Excellent illustrations of the bats discussed herein can be found at Bat Conservation International (http://www.batcon.org/index.php/all-about-bats/species-profiles.html) and the University of Michigan’s Animal Diversity Web site (http://animaldiversity.ummz.umich.edu/site/accounts/information/Chiroptera.html).
While species characteristics can differ greatly, the general anatomy of bats is shown below (Figure 3).
Physical Description of Colonial Bats
Big Brown Bat (Eptesicus fuscus)
- Recognition See Figure 1
- Weight 13 to 18 grams
- Body Length 1 to 5.1 inches
- Forearm 7 to 2.0 inches
- Wingspan 8 to 13.8 inches
- Color Dark brown, silky fur
The big brown bat can be distinguished from New York’s other colonial species by its larger size and distinctive “bull dog” humps on its nose. Big brown bats are hardy and favor buildings for winter roosting, with both males and females congregating together for hibernation. They are the most likely species to be found within buildings during the winter months. Summer maternity colonies may include a dozen to a few hundred individuals roosting behind chimneys, in enclosed eaves, hollow walls, attics, barns, and behind shutters and unused sliding doors. They can form colonies in rock crevices, beneath bridges, in hollow trees, and under loose bark. Litter size is generally 2 pups per year. Big brown juveniles can be distinguished from adults of smaller bat species by their short, rounded tragus and nose humps. Males roost in small groups or alone in the summer.
Big brown bats are widely distributed in the US. Their proximity to humans, coupled with the tendency to move about during temperature shifts, often brings big brown bats into human living quarters and basements. Big brown bats also hibernate in caves, mines, sewers, burial vaults, and underground harborage. They can travel hundreds of miles between their summering and wintering locations. Big brown bats may live up to 18 or more years.
Little Brown Bat (Myotis lucifugus, Figure 4)
- Weight 4 to 9 grams
- Body Length 1 to 3.9 inches
- Wingspan 0 to 10.6 inches
- Forearm 3 to 1.6 inches
- Foot Long hairs on toes extend beyond claws (Figure 5)
- Color Pale tan, red-brown, or dark brown
Little brown bats were one of the most common bats found in and near buildings, but white-nose syndrome has caused major population declines. Summer colonies are commonly found in dark, hot attics and roof spaces where maternity colonies can include hundreds of individuals. Colonies also form beneath shingles and siding, in tree hollows, beneath bridges, and in caves.
Litter size is 1 in the Northeast; twins occasionally occur in other areas. Roosts are sometimes shared with big brown bats, though the latter is less tolerant of high temperatures. Separate groups of males and non-reproducing females tend to be smaller and roost in cool attics, behind shutters, under bark, in crevices, and within caves.
Generally, in August or September little brown bats in the eastern part of their range abandon buildings to hibernate in caves and mines. Hibernacula may be near summer roosts or up to a few hundred miles away. The life span of little brown bats can be up to 34 years.
Northern Long-eared Bat (Myotis septentrionalis, Figure 6)
- Weight 5 to 7 grams
- Body Length 9 to 3.9 inches
- Forearm 3 to 1.5 inches
- Wingspan 0 to 10.6 inches
- Ears Long, narrow, pointed tragus
- Color Brown, but not glossy; confusion may occur with little brown bats which have shorter ears and no long, pointed tragus
Northern long-eared bats generally are found roosting singly in the East, except for small maternity colonies, where up to 30 individuals may congregate. They prefer to roost in dead or dying trees and beneath shaggy tree bark, but also roost behind shutters, under wooden shingles, sheltered entryways of buildings, in roof spaces, and in barns. However, they rarely are observed in buildings and are unlikely to be encountered indoors in areas outside of Long Island. Litter size is 1 pup annually. Roosts sometimes are shared with little brown bats. The sexes likely segregate during the maternity period. In winter, these bats are thought to hibernate in caves and mines, but occasionally may be found in buildings. The northern long-eared bat recently was listed as threatened under the Endangered Species Act (https://www.fws.gov/Midwest/endangered/mammals/nleb/index.html).
Eastern Small-footed Bat
(Myotis leibii, Figure 7)
Weight 3 to 5 grams
Body Length 2.9 to 3.2 inches
Forearm 1.2 to 1.3 inches
Wingspan 8.3 to 9.8 inches
Ears Black, sometimes with orange chiggers
Color Long, glossy brown fur; black face mask and ears
Eastern small-footed bats are one of the smallest Myotis species in North America. They have a higher tolerance for cool temperatures, like big brown bats. Litter size is 1 pup annually. They prefer to roost in rocky outcrops and talus slopes during the summer, but also can be found in the cracks of stone bridges. They sometimes are found in buildings. In the winter, they use caves and mines for underground hibernation. The small-footed bat is a species of special concern in New York.
Indiana Bat (Myotis sodalist, Figure 8)
- Weight 5 to 8 grams
- Body Length 0 to 3.6 inches
- Forearm 4 to 1.6 inches
- Foot See Figure 5 for comparison of hair on foot of little brown bat
- Wingspan 4 to 11.0 inches
- Color Dull, gray/brown fur all over body; may be confused with little brown bats that have long toe hairs and contrasting fur coloration
Indiana bats tend to roost in trees beneath peeling bark and within crevices of snags during the summer. They are rarely found in manmade structures. Summer distribution is mainly limited to patchy areas within about 40 miles (65 km) of hibernation sites. During the winter, Indiana bats hibernate in caves and abandoned mines. It was listed as endangered prior to the arrival of white-nose syndrome, and population declines since 2008 have further reduced the likelihood of coming in contact with this species (https://www.fws.gov/Midwest/endangered/mammals/inba/index.html).
Physical Description of Solitary Bats
Eastern Red Bat (Lasiurus borealis, Figure 9)
- Weight 9 to 15 grams
- Body Length 7 to 4.5 inches
- Forearm 4 to 1.8 inches
- Wingspan0 to 13.0 inches; long, pointed wings
- Ears Very short and rounded
- Tail membrane Heavily furred on upper surface
- Color Bright orange to yellow-brown, usually with a distinctive white mark on the shoulders
Eastern red bats are solitary, coming together only to mate and migrate. Red bats typically spend summer days hidden in the foliage of deciduous trees. Litter size ranges from 1 to 4. Red bats often chase insects that are attracted to light such as street lamps, which may bring them close to people. Red bats are well-adapted for drastic temperature fluctuations. They do not hibernate in caves, but apparently in trees. Some migrate long distances. During migration red bats have been known to land on high-rise buildings and on ships at sea.
(Lasionycteris noctivagans, Figure 10)
- Weight 8 to 11 grams
- Body Length 8 to 4.6 inches
- Forearm 6 to 1.8 inches
- Wingspan 6 to 12.6 inches
- Ears Short, rounded, hairless
- Tail membrane Upper surface is sparsely furred on the anterior half
- Color Black with silver-tipped fur, some with dark brown, yellowish-tipped fur; may be confused with larger hoary bats, which have white patches of hair on the ears and wings, heavy fur on the upper surface of the tail membrane, and a distinctive throat “collar”
Silver-haired bats roost in a variety of harborages. A typical roost is behind loose tree bark. Other sites include tree hollows, woodpecker holes, and bird nests. They usually are a solitary species except when with young. They may be colonial and may roost in and on buildings. Litter size is 2. The sexes segregate through much of the summer range. During migration, silver-haired bats can be encountered in buildings (they favor open sheds, garages, and outbuildings rather than enclosed attics), in lumber piles, and on ships at sea.
Hoary Bat (Lasiurus cinereus, Figure 11)
- Weight 19 to 28 grams
- Body Length 8 to 5.6 inches
- Forearm 0 to 2.1 inches
- Wingspan 3 to 16.1 inches
- Ears Relatively short, rounded, edged with black, and with fur
- Tail membrane Completely furred on upper surface
- Color Dark, but many hairs are tipped in white, giving it a frosted appearance; these bats have a yellowish or orangish throat “collar”; they may be confused with the much smaller silver-haired bats, which lack fur patches and markings on the ears, markings on the throat, and have tail membranes that are only lightly furred on the upper surface
Hoary bats generally spend summer days concealed in tree foliage (often evergreens), rarely enter houses, and are not commonly encountered by people. At day roosts, they usually are solitary except when with young. Litter size is 2. The sexes segregate through most of the summer range. Hoary bats are one of the largest bat species in North America, powerful fliers, and accomplished migrants.
(Perimyotis subflavus, Figure 12)
- Weight 6 grams
- Body Length 8 to 3.7 inches
- Forearm 3 to 1.4 inches
- Wingspan 3 to 10.2 inches
- Color Light, yellowish fur with dark base, pale middle and dark tips; contrasting pinkish forearms and dark wing membranes
Tri-colored bats generally are found roosting in tree foliage during the summer, with limited records of individuals roosting in buildings. Hibernation sites usually are in caves and mines. Recent trends suggest that this species is in severe decline in New York and elsewhere in the Northeast.
General Biology of Bats
Voice and Sounds
Most bats in North America emit high frequency sounds (ultrasound), inaudible to humans and similar to sonar, to avoid obstacles, locate and capture insect prey, and to communicate. Bats also emit audible sounds that may be used for communication between individuals.
Bats generally mate in the fall and winter but females retain sperm in the uterus until spring, when ovulation and fertilization take place. Pregnant females may congregate in maternity colonies in buildings, behind chimneys, beneath bridges, in tree hollows, caves, mines, or other dark retreats. They do not build nests. Birth typically occurs from May through early July. Young bats grow rapidly and can fly within 3 to 4 weeks. Weaning occurs in July and August, after which nursery colonies disperse.
Hibernating bats prepare for winter around the first frost. Some species migrate relatively short distances, but others travel several hundred miles to reach their wintering location. Bats in northern US and Canada may hibernate from September through May. Some species fly during warm winter spells (e.g., big brown bats in the northeastern US).
New York’s migratory bats (eastern red, silver-haired, and hoary bats) spend their summers in the state, but migrate south for the winter. They do not hibernate underground or in homes.
The human-made structures that bats tend to inhabit usually are in locations with significant exposure to sunlight.
Bats in New York are insectivorous, feeding on a variety of flying insects. Although there are some limitations, such as body size, flight capabilities, and jaw opening, insectivorous bats apparently consume a wide range of prey.
The diet of little brown bats includes mayflies, midges, mosquitoes, caddis flies, moths, and beetles. An individual bat can consume insects equal to 1/3 its body weight in ½ hour of foraging. Big brown bats may fill their stomach in about an hour (roughly 0.1 ounce per hour) with prey including beetles, moths, flying ants, true bugs, mayflies, caddis flies, and other insects. The nightly consumption of insects by a colony of bats can be extremely large.
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 (Figure 13).
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.
Openings of these dimensions are not uncommon in older wood frame structures where boards have shrunk, warped, or loosened. Big brown bats may hibernate in the cooler recesses of heated buildings, and they may suddenly appear (flying indoors or outdoors) in midwinter during a warm spell or a cold snap as they move about adjusting to the temperature shift.
Confirmation of Presence
We recommend 2 ways to confirm the presence of bats in a structure. The first is to perform a detailed building inspection (interior and exterior). Discovery of rub marks, bat guano, and sightings of bats, coupled with client information usually are sufficient to confirm the presence of bats.
The second way to confirm the presence of bats is a bat watch. It can be conducted by 2 people posted at opposite corners of a structure (more may be necessary to observe large or complex sites). An evening watch begins about 30 minutes before dark and a morning watch begins about an hour before dawn.
Observations should continue for approximately 1 hour. Bat watches can help indicate exit and entry points and provide an estimate of the number of adult bats. If no bats are detected on the first bat count, we recommend conducting up to 5 bat counts to compensate for the possible influence of weather conditions, bat sensitivity to observers, noisy or inexperienced observers, and improper use of light. Not all bats will exit every night. Observations can be enhanced with a standard flashlight, but be certain to project the beam as far as possible away from the exit hole that is being observed. Bright light will increase the reluctance of bats to exit and may result in an incomplete count of the colony. A valuable observation aid is a powerful, rechargeable flashlight equipped with a red filter. Also, an electric headlamp supplied with rechargeable batteries and fitted to a climbing or caving helmet allows hands-free illumination when exploring roost locations. Bats are sensitive to light intensity and can visually discriminate shapes and patterns in extremely low-light situations. They see in black and white, so low-contrast illumination and soft shadows produced by red light have little effect on 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 (Figure 14). 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).
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 (Figure 15), causing multiple spotting and staining on sides of buildings, windows, patio furniture, automobiles, and objects near entry and exit holes, or beneath roosts.
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., Figure 16) are sometimes found crawling on the surface of beams or around holes leading to secluded recesses used by bats.
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.
Area fumigation with a total-release pyrethrum-based aerosol may be an appropriate solution for knockdown of arthropods within an enclosed space, but only after bats have departed. For long-term control of arthropods, lightly dust appropriate surfaces (affected attic beams, soffits) with boric acid powder or diatomaceous earth. A NWCO in NY must be a licensed pesticide applicator to apply any pesticides. Carefully read all product labels before using any pesticide. Neither rabies nor Lyme disease is transmitted by any arthropods associated with bats.
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 (Figure 17).
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 a client or others in the building:
- were awakened to find a bat flying in their room,
- found a bat in a room with an unattended child, whether sleeping or not, or
- 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.
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.
Damage Prevention and
Costs for remedial services are highly variable, depending on the nature of the problem and who will do the work. For example, to fabricate a few bat check-valves on the “average” 2-story house would probably require 2 workers about a half day, mostly on stepladders, and less than $50 in materials. Much more time would be required to seal all the other active and potential exit and entry holes. In addition, if a deteriorated roof, eaves, or other woodwork needs replacement, costs can increase rapidly.
In outdoor settings, swap white-light bulbs for bulbs less attractive to insects. Illumination has been reported to have limited effectiveness at moving bats out of structures. Floodlights strung through an attic to illuminate all roosting sites may cause bats to leave. For this method to be effective, the light level must be bright by human standards. Fluorescent bulbs may be used. In some situations, such lighting is difficult, costly, and is an electrical hazard. Note that bright light may drive bats into wall voids where control can be more difficult.
Air drafts have been successful in repelling bats in areas where building owners can open doors and windows, or create strong breezes with electric fans. The addition of wall and roof vents will enhance this effort, as this will lower roost temperatures. The above-described measures will increase the thermoregulatory burden on the bats, making the roost less desirable.
Colonies in soffits, behind cornices, and other closed-in areas can be discouraged by opening these areas to eliminate dark recesses. Discourage bats from roosting behind shutters by removing the shutters completely or by adding small blocks at the corners to space them a few inches away from the wall.
Eviction/venting and exclusion is the gold standard for eliminating and preventing bats from residing in structures. It is tedious to locate all active and potential openings available to bats. Active holes can be identified by rub marks, guano, and sometimes odor. Except for the actively used holes, seal all gaps of ¼ x 1½ inches and openings 5/8 x 7/8 inches or greater. Bats use some of the same holes in buildings through which heat (or cooled air) is lost. Bat-proofing can reduce energy costs for the client. As with any exclusion intervention, the excluded animals will be forced to go elsewhere. The shift may be to another building nearby.
There is no guarantee that bats will use a bat house, but research has shown that bat houses can be successfully occupied during and after an eviction. Ideally, bat houses should be erected a few months to a year before a scheduled exclusion to give bats time to find and explore the new roosting option. Bat houses should be installed near the original roost to increase the likelihood of bats finding the new habitat. Choosing the proper location, placement, design, color, and materials are all important factors for increased success.
Timing is important to reduce the risk of separating adults from flightless young. Although regulation does not prohibit removal of bats during the pup season, eviction and subsequent exclusion generally should not be attempted between May 15 and August 15. One-way eviction devices installed during the maternity season will allow adult bats to leave the structure but flightless young bats will be trapped inside. Mothers of trapped pups may attempt to reach their young by flying back into the living spaces of homes. Trapping bats inside an attic will increase the chance of them finding their way into the living quarters of a home as they search for a way out. An alternative to exclusion is to seal unused holes, but leave active holes open from May 15 until August 15. During the maternity season, your primary strategy should be to concentrate efforts on locating and sealing off entries into the client’s living spaces. In structures used by bats for hibernation, eviction and venting during the winter months should be avoided as well. Clients should be made aware of the increased chances of exposure that are the result of eviction/venting at the wrong time of year.
Exclusion materials and methods for bats are less rigid than for rodents, as bats do not chew into structures. Caulk, flashing, screening, and insulation often are needed to complete an exclusion job. The combination of materials used will depend on the location, size, and number of openings and the need for ventilation. Weather stripping and knitted-wire mesh (Guard-All®, Stuf-fit®) are best applied during dry periods when wood cracks are widest. Caulk can be applied with a caulking gun (in gaps up to 0.4 inch wide) and include latex, butyl, and acrylic compounds, which last about 5 years. Elastomeric caulks, such as silicone rubber, will last indefinitely, expand and contract, will not dry or crack, and can tolerate temperature extremes.
To prevent bats from entering chimney flues, completely enclose the flue discharge area with rust-resistant spark arresters or pest screens secured to the top of the chimney. They should not be permanently attached (e.g., with screws) in case they must be rapidly removed in the event of a chimney fire. Review fire codes before installing flue covers. Dampers should be kept closed except during the heating season.
Oakum packs easily and firmly into small cracks. Other fillers include sponge rubber, glass fiber, knitted-wire mesh, and quick-setting putty. Self-expanding polyurethane foam applied from pressurized containers can be used for openings larger than 3 inches. It must be applied with caution so clapboards, shingles, and other surfaces are not lifted. Surfaces that are exposed should be sealed with epoxy paint to prevent insect infestation and ultraviolet degradation. Conventional draft sweeps (metal, rubber) and other weather stripping supplies (felt, vinyl, metal) will seal the space between a door bottom and the threshold or around windows (Figures 18 and 19).
Treat attic and basement doors whenever the gap exceeds ¼ inch. Flashing may be used to close gaps at joints (e.g., where the roof meets a chimney). Materials include galvanized metal, copper, aluminum, stainless steel, and self-adhesive stainless steel “tape.” A potentially useful intervention for the wall-ceiling interface is the application of a wide 45° molding strip to eliminate the 90° angle corner and force the bats to roost in a more exposed area. Insulation provides some barrier to bat movements. It is available in several forms and types including fiberglass, rock wool, urethane, vermiculite, polystyrene, and extruded polystyrene foam. Inorganic materials are fire and moisture resistant. The safest appear to be fiberglass and rock wool.
The mesh size of screen must be small enough to prevent access of bats and other species. Hardware cloth with ¼-inch mesh will exclude bats and mice (Figure 20). Screen with 16 meshes per inch will exclude most insects. Soffits (underside of overhanging eaves) usually have vents of various shapes and sizes. The slots should not exceed ¼- x 1-inch and should be covered on the inside with insect mesh.
Exclusion on tile roofs can be difficult. Bats often roost under Spanish or concrete tile roofing by entering the open ends at the lowermost row or where the tiles overlap. Tight-fitting plugs are difficult to make due to the variation in opening sizes and thermal expansion and contraction. A layer of coarse fiberglass batting laid under the tiles so that bats entering holes contact the fiberglass can be an effective barrier. A layer of knitted wire mesh also will work well for this purpose and will not hold moisture. Bats also may be excluded from the tiles if rain gutters are installed directly under the open ends. Gaps under corrugated and galvanized roofing may be closed with knitted-wire mesh, self-expanding foam (avoid causing roofing to lift), or with fiberglass batting (may retain moisture).
One-way doors are excellent for moving bats out of structures. A variety of 1-way doors and check-valves are available, and no single device is suitable for every situation. Install 1-way doors on holes that are actively used by bats to enter or exit the structure. One-way doors should be left in place for at least 3 to 5 days. During periods of inclement weather (e.g., rain), 1-way doors should be left in place longer.
The basic design attaches netting (fiberglass mosquito netting works well) around an exit hole except at the bottom where the bats will escape. Designs must be open enough so they do not interfere with bats exiting the hole (Figure 21).
When their routine exit points are blocked, bats may seek alternative entry points, often causing some bats to find their way into living quarters of homes. Do not lay netting flush against the wall, as this will prevent bats from exiting. Fold the netting to provide the exiting bats a little gap to move into and then down and out. The width and shape of these “check valves” (allowing bats to exit but not enter) is highly variable so they can cover the necessary exit points such as a single hole, a series of holes, or a long slit-like opening. The top can be much larger than the bottom. The length of the netting (the distance from the lowest enclosed point of egress to the bottom of the netting) should be about 3 feet, and stick out about 3 to 5 inches from the wall so the bats can crawl beneath the screen to leave. The above specifications usually are sufficient to keep bats from reentering the space.
Tubes, such as the Batcone® (Figure 22), provide another tool to exclude bats. Center the tube hole over the exit used by the bats to provide an easy way out.
Frightening devices are not appropriate for the control of bats. Ultrasonic devices have been developed for certain specialized commercial applications, but generally are too expensive for domestic use.
Repellents and Toxicants
In New York, any use of toxicants or repellents by NWCOs requires the NWCO to have a pesticide applicator license.
Before using any product, you must check the New York State Pesticide Administrator Database (NYSPAD) to see if the product is registered for use in NY and for the target species. For example, if the product is registered for use on squirrels, it cannot be used for bats.
Many chemical aromatics and irritants have been proposed and tested for bat repellency, though efficacy has proven very limited. The following is presented as an example of a repellent that may be effective for bats. A NWCO must have a pesticide applicator license to use repellents. The NWCO must determine if the product is legal to use in NY and if it is labeled for use on bats.
Customers may ask about using moth balls or insect spray. Only products labeled specifically for use as a bat pesticide can be used to deter bats. Naphthalene is registered as a pesticide for bats in New York, which means that a NWCO with a commercial pesticide applicator license can purchase and use naphthalene products specified as a bat pesticide.
Naphthalene flakes may help to repel a bat colony if the site is confined and has little or no ventilation, but this is an unlikely scenario. The effective application rate of naphthalene is high and could endanger people using the building. Human exposure to naphthalene can result from inhalation, consumption, or absorption through the skin.
No toxicants are registered for the control of bats.
Shooting bats is not practical and it is not legal in many states.
Trapping of bats not recommended. Bat Conservation International (BCI) does not promote NWCOs who use bat traps. Eviction/venting and exclusion is less complicated, less time-consuming, more effective, and requires no handling of bats. Trapping of protected species, such as the northern long-eared bat (Myotis septentrionalis), is not legal in New York.
Lone Bat Encounters
Occasionally, lone bats are found inside houses. Ask the client to watch the bat and attempt to close it off in a small section/room of the building, as finding a bat again is extremely difficult. If the bat is still flying upon your arrival, close doors, cabinets, closets, and windows to reduce potential hiding areas and possible escapes. Wear leather gloves and take a wide-mouthed plastic storage container or tube (Figure 23). Wait for the bat to tire and land. DO NOT LEAVE THE ROOM. When the bat lands, place the storage container or tube over the bat. Slide a lid or thin piece of cardboard between the bat and the wall, trapping the bat inside the container. Tape the cover in place. If the bat is to be tested for rabies, the head must not be damaged.
Interview the client thoroughly to determine if any people have been exposed to the bat. If you are certain there has been no human exposure, release the bat outdoors on a surface at least 5 feet above the ground. Familiarize yourself with the rabies submission procedure before offering bat control services, as these events may not occur during normal business hours.
Bats can be released outside on the same property they were captured, provided they have not bitten people or pets and there was no chance of human rabies exposure (see Wildlife Disease Module). Bats should be released on a tree at least 5 feet above the ground. Bats should not be relocated to another property. There is no value in relocating bats, as they can easily return if they chose to.
Bats are a rabies vector species. Moving them is not recommended.
Some bats are protected, and all are beneficial to the environment. Bats should only be euthanized if they are ill, or if a potential rabies exposure has occurred.
All bats that may have been exposed to people or pets should be tested for rabies. Other bats need to be disposed of in accordance with local ordinances. In most cases, bats can be disposed of by burying them in the ground to a depth that won’t be dug up by other animals (approximately 12” or more).
Sanitation and Cleanup
After bats are excluded, or have departed at the end of the summer, measures must be completed to make re-infestation less likely, and to eliminate odor and bioaerosols. It sometimes is useful to apply a pyrethrum-based, total-release, aerosol insecticide to eliminate unwanted arthropods. Read and follow the label to make certain the pesticide is labeled for both the target pest and the site where it will be applied.
Safe handling and removal of bat guano has been discussed previously. In addition to the bulky accumulations of excreta, often diffuse deposits of guano occur under and among insulation materials, caked urine and guano on roof beams, and splattered urine on windows. Such clean-up work during hot summer weather may be the least desirable activity of a management program, but it is necessary.
All caked or crystallized bat urine and droppings should be scraped and wire-brushed from all roof and attic beams. For this procedure, workers should take the same precautions as outlined for histoplasmosis-related work. Accumulated excreta and contaminated insulation should be sealed in plastic bags and removed for disposal in accordance with state and local laws. Remove all remaining droppings and debris with a vacuum cleaner, preferably one that has a water filter to reduce the amount of dust that escapes in the exhaust.
Wash all contaminated surfaces with soap and water. Allow the surfaces to dry and disinfect them by misting or swabbing on a solution of 1 part household bleach and 20 parts tap water. Ventilate the roost site to allow odors and moisture to escape. Installation of tight-fitting window screens, roof and/or wall ventilators in attics will enhance this process. Sanitation and cleanup accompanies bat-proofing and exclusion measures. It does not replace them.
Material was updated and adapted from the book, Prevention and Control of Wildlife Damage, 1994, published by the University of Nebraska–Lincoln Extension.
Reviewers of Original Document
- Michael Mitchell of Alabama;
- Reginald Murray of Oklahoma Wildlife Control, LLC;
- Eddie Hope of Virginia Professional Wildlife Removal Services, LLC;
- Mike Mengak of Warnell School of Forest Resources, University of Georgia; and
- Jim Armstrong of School of Forestry and Wildlife Sciences, Auburn University.