Bats
Bats are flying mammals with forelimbs developed as wings. Other mammals, such as flying squirrels or gliding phalangers, can glide limited distances, but only bats are capable of true flight.
Identification
Bats, the only mammals that truly fly, belong to the order Chiroptera. Their ability to fly, their secretiveness, and their nocturnal habits have contributed to bat folklore, superstition and fear. They are worldwide in distribution and include about 900 species, second in number only to Rodentia (the rodents) among the mammals. Among the 40 species of bats found north of Mexico, only a few cause problems for humans (note that vampire bats are not found in the United States and Canada). Bats congregating in groups are called colonial bats; those that live alone are known as solitary bats.
Region and Habitat
Solitary bats typically roost in tree foliage or under bark, but occasionally are found associated with buildings, some only as transients during migration. These include Keen’s bat (Myotis keenii), the red bat (Lasiurus borealis), the silver-haired bat (Lasionycteris noctivagans) and the hoary bat (Lasiurus cinereus).
Several species of bats have been included here, with significant interspecific differences that need to be clarified if well-planned, comprehensive management strategies are to be developed. Any problems caused by bats are limited to species distribution; thus animal damage control personnel need not be concerned with every species. Colonial and solitary bats have obvious differences that serve to separate the species into groups.
COLONIAL BATS
Little brown bat (Myotis lucifugus)
Recognition
forearm — 1.34 to 1.61 inches (3.4 to 4.1 cm)
wingspan — 9.02 to 10.59 inches (22.9 to 26.9 cm)
ears — 0.55 to 0.63 inches (1.4 to 1.6 cm) foot — approximately 0.39 inches (1.0 cm); long hairs on toes extend beyond claws.
Color
Pale tan through reddish brown to dark brown, depending on geographic location. The species is a rich dark brown in the eastern United States and most of the west coast. Fur is glossy and sleek. Confusion may occur with a few other “house” bat species. In the East, it may be confused with Keen’s bat (M. keenii), which has longer ears [0.69 to 0.75 inches (1.7 to 1.9 cm)] and a longer, more pointed tragus (the appendage at the base of the ear). In the West, it resembles the Yuma myotis (M. yumanensis), which has dull fur and is usually smaller. However, the Yuma myotis and little brown may be indistinguishable in some parts of the northwestern United States where they may hybridize.
Habits
This is one of the most common bats found in and near buildings, often located near a body of water where they forage for insect prey. Summer colonies are very gregarious, commonly roosting in dark, hot attics and associated roof spaces where maternity colonies may include hundreds to a few thousand individuals. Colonies may 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 some other areas. The roost is often shared with the big brown bat (E. fuscus) though the latter is less tolerant of high temperatures; M. keenii may also share the same site. Separate groups of males tend to be smaller and choose cooler roosts within attics, behind shutters, under tree bark, in rock crevices, and within caves.
In the winter, little brown bats in the eastern part of their range abandon buildings to hibernate in caves and mines. Such hibernacula may be near summer roosts or up to a few hundred miles (km) away. Little is known of the winter habits of M. lucifugus in the western United States.
The life span of little brown bats has been established to be as great as 31 years. The average life expectancy, however, is probably limited to only a few years.
Big brown bat (Eptesicus fuscus)
Recognition
forearm — 1.65 to 2.01 inches (4.2 to 5.1 cm)
wingspan — 12.80 to 13.78 inches (32.5 to 35.0 cm)
ears — with rounded tragus
Color
From reddish brown, copper colored, to a dark brown depending on geographic location. This is a large bat without distinctive markings. Confusion may occur with the evening bat (Nycticeius humeralis) though the latter is much smaller.
Habits
This hardy, rather sedentary species appears to favor buildings for roosting. Summer maternity colonies may include a dozen or so and up to a few hundred individuals, roosting behind chimneys, in enclosed eaves, in hollow walls, attics, barns, and behind shutters and unused sliding doors. They also form colonies in rock crevices, beneath bridges, in hollow trees, and under loose bark. Litter size is 2 in the East to the Great Plains; from the Rockies westward 1 young is born. E. fuscus frequently shares roosts with M. lucifugus in the East, and with M. yumanensis, Taderida, and Antrozous in the West. Males typically roost in smaller groups or alone during the summer.
The big brown bat is one of the most widely distributed of bats in the United States and is probably familiar to more people than any other species. This is partially due to its large, easy-to-observe size, but also to its ability to overwinter in buildings (attics, wall spaces, and basements). Its close proximity to humans, coupled with its tendency to move about when temperature shifts occur, often brings this bat into human living quarters and basements in summer and winter. Big browns also hibernate in caves, mines, storm sewers, burial vaults, and other underground harborage. While E. fuscus will apparently travel as far as 150 miles (241 km) to hibernacula, the winter quarters of the bulk of this species are largely unknown. Big brown bats may live as long as 18 years.
Mexican free-tailed bat (Tadarida brasiliensis)
Recognition
forearm — 1.42 to 1.81 inches (3.6 to 4.6 cm)
wingspan — 11.42 to 12.80 inches (29.0 to 32.5 cm); long narrow wings
tail (interfemoral) membrane — does not enclose the lower one-third to one-half of the tail, hence the name free-tailed
foot — long, stiff hairs as long as the foot protrude from the toes.
Color
Dark brown or dark gray. Fur of some individuals may have been bleached to a pale brown due to ammonia fumes from urine and decomposing guano. Confusion is not likely to occur with other species that commonly inhabit human buildings.
Habits
T. brasiliensis forms the largest colonies of any warm-blooded animal, establishing sizable colonies in buildings, particularly on the West Coast and in the Gulf states from Texas east. Hundreds to thousands may be found in buildings or under bridges. It is primarily a cave bat in Arizona, New Mexico, Oklahoma, and Texas; buildings are used as temporary roosts during migrations. Litter size is 1. Taderida often share roosts with other species. In the West, for example, they may be found in buildings with A. pallidus, M. yumanensis, and E. fuscus. Some males are always present in the large maternity colonies, but they tend to segregate in separate caves. A few Taderida may overwinter in buildings as far north as South Carolina in the East and Oregon in the West. Most of this species migrate hundreds of miles to warmer climes (largely to Mexico) for the winter.
Pallid bat (Antrozous pallidus)
Recognition
forearm — 1.89 to 2.36 inches (4.8 to 6.0 cm)
wingspan — 14.17 to 15.35 inches (36.0 to 39.0 cm)
ears — large; widely separated and more than half as broad as long. The ears are nearly half as long as the combined length of the bat’s head and body.
eyes — large
Color
pale, upper parts are light yellow, the hairs tipped with brown or gray. Underparts are pale creamy, almost white. This large, light-colored bat is relatively easy to recognize. Confusion with other species that commonly inhabit human buildings is not likely to occur.
Habits
Maternity colony size ranges from about 12 to 100 individuals. Roost sites include buildings, bridges, and rock crevices; less frequently, tree cavities, caves, and mines. Litter size is most commonly 2. The roost is frequently shared with T. brasiliensis and E. fuscus in the West. While groups of males tend to segregate during the nursery period (sometimes in the same building), other males are found within the maternity colony. An interesting feature of pallid bats is that they fly close to the ground, may hover, and take most prey on the ground, not in flight. Prey includes crickets, grasshoppers, beetles, and scorpions. They will also forage among tree foliage. Pallid bats are not known to make long migrations, though little is known of their winter habits.
Yuma myotis (Myotis yumanensis)
Recognition
forearm — 1.26 to 1.50 inches (3.2 to 3.8 cm)
wingspan — about 9.25 inches (23.5 cm)
ears — 0.55 to 0.59 inches (1.4 to 1.5 cm)
foot — 0.39 inches (1.0 cm)
Color
Light tan to dark brown; underside is whitish to buffy. Confusion may occur in the West with M. lucifugus, though the latter tends to have longer, glossier fur, and is larger. In the Northwest, hybridization occurs with M. lucifugus, making the species indistinguishable.
Habits
Maternity colonies, up to several thousand individuals, form in the summer in attics, belfries, under bridges, and in caves and mines. Litter size is 1. Males typically segregate during the nursery period and roost as solitary individuals in buildings and other suitable harborage. M. yumanensis is more closely associated with water than is any other North American bat species. Nearly all roosts have open water nearby. This species is not as tolerant as M. lucifugus of high roost temperatures and will move to cooler niches within a building when temperatures rise much above 100o F (37.8o C). M. yumanensis abandons maternity colonies in the fall, but its winter habitat is not known.
Evening bat (Nycticeius humeralis)
Recognition
forearm — 1.30 to 1.54 inches (3.3 to 3.9 cm)
wingspan — 10.24 to 11.02 inches (26.0 to 28.0 cm)
ears — with short, curved, and rounded tragus
Confusion may occur with the big brown bat (E. fuscus), which can be readily distinguished by its larger size. It bears some resemblance to the somewhat smaller little brown bat (M. lucifugus) but can be identified by its characteristic blunt tragus.
Color
Medium brown with some variation to yellow-brown in subtropical Florida. No distinctive markings.
Habits
Summer maternity colonies in buildings may consist of hundreds of individuals. Litter size is usually 2. Colonies also form in tree cavities and under loose tree bark. In the Southeast, T. brasiliensis commonly inhabits the same building with N. humeralis. This is one of the most common bats in towns throughout the southern coastal states. Very little is known about this species, and virtually nothing is known of its winter habitat except that it almost never enters caves.
SOLITARY BATS
Keen’s bat (Myotis keenii)
Recognition
forearm — 1.26 to 1.54 inches (3.2 to 3.9 cm)
wingspan — 8.98 to 10.16 inches (22.8 to 25.8 cm)
ears — 0.67 to 0.75 inches (1.7 to 1.9 cm); with a long, narrow, pointed tragus
Color
Brown, but not glossy; somewhat paler in the East. Confusion may occur with M. lucifugus, which has glossy fur, shorter ears, and does not have the long, pointed tragus.
Habits
Excluding small maternity colonies (up to 30 individuals are on record), M. keenii are generally found singly in the East. Roosting sites include: behind shutters, under wooden shingles, sheltered entryways of buildings, in roof spaces, in barns, and beneath tree bark. In the West, this bat is known as a solitary species, roosting in tree cavities and cliff crevices. Litter size is probably 1. The roost is sometimes shared with M. lucifugus. The sexes probably segregate during the nursery period. In winter, these bats hibernate in caves and mines.
Red Bat (Lasiurus borealis)
Recognition
forearm — 1.38 to 1.77 inches (3.5 to 4.5 cm)
wingspan — 11.42 to 13.07 inches (29.0 to 33.2 cm); long, pointed wings
ears — short rounded
tail membrane — heavily furred on upper surface, with a distinctive long tail.
Color
Bright orange to yellow-brown; usually with a distinctive white mark on the shoulders. Confusion may occur with the hoary bat (L. cinereus), which is frosted-gray in appearance and larger.
Habits
Red bats live solitary lives, coming together only to mate and migrate. Few people are familiar with this species. They typically spend summer days hidden in the foliage of deciduous trees. The number ofyoung ranges from 1 to 4, averaging 2.3. These bats often chase insects that are attracted to lights, such as street lamps. It is this behavior that most likely brings them in close proximity to people. L. borealis is well-adapted for surviving drastic temperature fluctuations; it does 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.
Silver-haired bat (Lasionycteris noctivagans)
Recognition
forearm — 1.46 to 1.73 inches (3.7 to 4.4 cm)
wingspan — 10.63 to 12.20 inches (27.0 to 31.0 cm)
ears — short, rounded, hairless
tail membrane — upper surface is sparsely furred on the anterior one-half.
Color
Usually black with silver-tipped fur; some individuals with dark brown, yellowish-tipped fur. Confusion sometimes occurs with the larger hoary bat (Lasiurus cinereus), which has patches of hair on the ears and wings, heavy fur on the entire upper surface of the tail membrane, and has a distinctive throat “collar.”
Habits
The silver-haired bat roosts in a wide variety of harborages. A typical roost might be behind loose tree bark; other sites include tree hollows and bird nests. This species is solitary except when with young. Additionally, there are unconfirmed reports that it is sometimes colonial (Dalquest and Walton 1970) and may roost in and on buildings. The litter size is 2. The sexes segregate through much of the summer range. L. noctivagans hibernates in tree crevices, under loose bark, in buildings (including churches, sky scrapers, and wharf houses), hulls of ships, rock crevices, silica mines, and non-limestone caves. It also may migrate, during which time it is 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)
Recognition
forearm — 1.81 to 2.28 inches (4.6 to 5.8 cm)
wingspan — 14.96 to 16.14 inches (38.0 to 41.0 cm)
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. This bat also has a yellowish or orangish throat “collar.” Confusion may sometimes occur with the much smaller silver-haired bat (Lasionycteris noctivagans), which lacks the fur patches and markings on the ears, markings on the throat, and has a tail membrane that is only lightly furred on the upper surface.
Habits
Hoary bats generally spend summer days concealed in tree foliage (often in evergreens), rarely enter houses, and are not commonly encountered by people. L. cinereus at their day roosts are usually solitary except when with young. The litter size is 2. The sexes segregate through most of the summer range. This is one of the largest bats in North America, a powerful flier, and an accomplished migrant. Records indicate that some L. cinereus may hibernate in northern parts of their range.
Fun Facts
Most North American bats emit high frequency sounds (ultrasound) inaudible to humans and similar to sonar, in order to avoid obstacles, locate and capture insect prey and to communicate.
Bats generally mate in the fall and winter, but the female retains the sperm in the uterus until spring. Young bats grow rapidly and are able to fly within 3 weeks. Weaning occurs in July and August, after which the nursery colonies disperse.
Bats prepare for winter around the time of the first frost. Some species migrate relatively short distances, whereas certain populations of the Mexican free-tailed bat may migrate up to 1,000 miles (1,600 km). Bats in the northern United States and Canada may hibernate from September through May. Hibernation for the same species in the southern part of their range may be shorter or even sporadic. Some may fly during warm winter spells (as big brown bats may in the northeastern part of the United States). Bats often live more than 10 years.
Damage Identification
Bat Presence
Bats often fly about 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.
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. Other openings may be found under loose-fitting doors, around windows, gaps around various conduits (wiring, plumbing, air conditioning) that pass through walls, and through utility vents.
Bats are able to squeeze through narrow slits and cracks. For purposes of bat management, one should pay attention to any gap of approximately 1/4 x 1 1/2 inches (0.6 x 3.8 cm) or a hole 5/8 x 7/8 inch (1.6 x 2.2 cm). The smaller species require an opening no wider than 3/8 inch (0.95 cm), that is, a hole the diameter of a US 10-cent coin. Openings of these dimensions are not uncommon in older wood frame structures where boards have shrunk, warped or otherwise become loosened.
The discovery of one or two bats in a house is a frequent problem. In the Northeast, big brown bats probably account for most sudden appearances. Common in urban areas, they often enter homes through open windows or unscreened fireplaces. If unused chimneys are selected for summer roosts, bats may fall or crawl through the open damper into the house. Sometimes bats may appear in a room, then disappear by crawling under a door to another room, hallway, or closet. They may also disappear behind curtains, wall hangings, bookcases, under beds, into waste baskets, and so forth. Locating and removing individual bats from living quarters can be laborious but is important. If all else fails, wait until dusk when the bat may appear once again as it attempts to find an exit. Since big brown bats may hibernate in the cooler recesses of heated buildings, they may suddenly appear (flying indoors or outdoors) in midwinter during a warm spell or a cold snap as they move about to adjust to the temperature shift.
Roosting Sites
Bats use roosting niches that are indoors (human dwellings, outbuildings, livestock quarters, warehouses), semi-enclosed (loading docks, entrance foyers), partially sheltered (porches, carports, pavilions, highway underpasses, bridges), and open structural areas (window shutters, signs). Once there, active bats in and on buildings can have several economic and aesthetic effects, often intertwined with public health issues. Unusual roosting areas include wells, sewers, and graveyard crypts. Before considering control measures, verify that bats are actually the cause of the problem.
Rub Marks
Surface areas on walls, under loose woodwork, between bricks and around other bat entryways 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 these 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 heavily by bats.
Noise
Disturbing sounds may be heard from vocalizations and 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.
Guano and Urine
Fecal pellets indicate the presence of animals and are found on attic floors, in wall recesses, and outside the house at its base.
Bat excrement produces an unpleasant odor as it decomposes in attics, wall spaces and other voids. The pungent, musty, acrid odor can often be detected from outside a building containing a large or long-term colony.
Bats also urinate and defecate in flight, causing multiple spotting and staining on sides of buildings, windows, patio furniture, automobiles and other objects at and near entry/exit holes or beneath roosts.
The close 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 (Frantz 1988).
Public Health Issues
Bats are distinct from most vertebrate pests that inhabit human dwellings because of the potential for transmitting rabies and histoplasmosis.
Legal Status
The lethal control of bats, even when there is a proven potential danger to humans, often is subjected to careful scrutiny and interagency coordination. A survey of federal legislative actions, court decisions, and agency interpretations concerning bats can be found in Bat Management in the United States. Some states have laws that specifically mention bats, either providing or denying protection. Others have legislation that applies to bats only by interpretation, since bats may be considered non-game wildlife or indigenous state mammals. Some bats have protection as either federal or state-listed endangered species, but the same state may not protect other species of bats. Enforcement and public education must accompany legislation to accomplish the intended goal of protecting the public and saving endangered bats. Familiarity with the appropriate federal and state laws should precede any nuisance management activities.
Damage Prevention and Control Methods
Bat Watch for Infestation Confirmation
To confirm that bats are actually roosting in or on a building, look for bats flying in and out of a site and/ or for signs of infestation. A bat watch can be conducted by two people (more may be necessary to observe large or complex sites) posted at opposite corners of a structure. An evening watch begins about 30 minutes before dark and a morning watch begins about 1 hour before dawn. Observations should continue for approximately 1 hour. Such observations can indicate exit/ entry points and the number of bats. With practice, distinguishing some bat species may also be possible. For example, compared to the big brown bat, the little brown bat is noticeably smaller in size, and its flight has more rapid wing beats, and more rapid turning and darting.
It may be necessary to watch for more than one night to compensate for weather conditions, bats’ sensitivity to observers, noisy or inexperienced observers, and improper use of light. Observations can be enhanced with a standard flashlight, but be certain to keep the bright part of the beam as far as possible away from the exit hole being observed. Bright light will increase bats’ reluctance to exit and may result in an incomplete exit of the colony. A valuable observation aid is a powerful, rechargeable flashlight equipped with a plastic, red pop-off filter (similar to the Kodak Wratten 89B). Also, an electric headlamp, supplied with rechargeable batteries and fitted to a climbing or spelunking helmet, allows hands-off illumination outdoors as well as indoors when exploring roost locations. Bats are sensitive to light intensity and can visually discriminate shapes and patterns in extremely low light situations. They can only see in black and white; hence, the low-contrast illumination and soft shadows produced by red light has little effect on bats.
Locating the Roost(s)
It is not always possible or convenient to conduct a bat watch. Thus, a detailed inspection inside the building for bats or bat sign may be necessary to find specific roosts. Daytime is best, especially during the warmer part of the day. Bats roost in the most varied kinds of buildings and in every part from cellar to attic. Some types of buildings appear preferable (older houses, churches, barns, proximity to water) as do certain roost locations therein, especially areas with little disturbance, low illumination, little air circulation, and high temperatures. Often it is easy to locate bats, especially in warm weather in attics or lofts, where they may hang in clusters or side-by-side from the sloping roof lath, beams, and so forth. However, bats have the ability to find crevices and cavities, and if disturbed may rapidly disappear into the angles between converging beams, behind such beams or wallboards, into mortise holes on the underside of beams, and into the multilayered wall and roof fabrications. If bats cannot be openly observed, usually there are various interior and exterior signs of their presence. Often there are multiple roost sites within or on a single building.
Problem Assessment
Once it has been confirmed that bats are present, one must determine if there is damage, if there is a health risk, and if some intervention is warranted. There are circumstances in which “no action” is the correct action because of the beneficial role of bats. In cases where there is risk of contact, damage from excreta accumulations, stains, and so on, intervention may be necessary.
Timing
With the exception of disease treatment and removal of the occasional bat intruder, timing becomes an important planning consideration. Management procedures must not complicate an already existing problem and should emphasize bat conservation. Therefore, all interventions should be initiated before the young are born or after they are weaned and able to fly. Thus, the annual opportunity extends from about mid-August to mid-May for much of North America. Treatments might otherwise result in the unnecessary death of animals (especially young unable to fly) trapped inside, offensive odors, and attraction of arthropod scavengers.
Removal of Occasional Bat Intruders
A bat that has blundered into the living quarters of a house will usually find its way out by detecting air movement. When no bite or contact with people or pets has occurred, the simplest solution for “removing” the bat is to try to confine it to one room, then open windows and doors leading outdoors and allow it to escape. If the bat is present at night, the lights should be dimmed to allow the animal to find open doors and windows; some light is necessary if an observer is to insure that the bat finds its way out. If bright lights are kept on, the bat may become confused and may seek refuge behind shelving, curtains, hanging pictures, or under furniture.
Healthy bats normally will not attack people even when chased. Chasing a flying bat with a folded newspaper, tennis racket, or stick will cause the bat to take evasive action, and a bat’s flight reversal to avoid a wall is often misinterpreted as an attack. These flailings, often futile, will cause a bat to seek safety wherever possible, making escape more difficult for the bat and more frustrating for the human.
If a bite or physical contact occurs, capture the bat without damaging its head and immediately contact a physician (see previous section regarding rabies treatment). Management of problems involving bat colonies require more complicated procedures and a greater time commitment.
NOTE
The Centers for Disease Control recommends that if there has been human or pet contact, or if it is unknown if there was contact, the bat should be destroyed (do not crush the head) and the public health department consulted. The Centers for Disease Control also recommends that if the bat was in a room with a sleeping person then it should be captured, destroyed without crushing the head, and submitted for testing. Consult your physician for more information.
Exclusion
Polypropylene netting checkvalves simplify getting bats out. Quality bat-proofing permanently excludes bats. Initiate control before young are born or after they are able to fly.
Repellents
Naphthalene: limited efficacy. Illumination. Air drafts/ventilation. Ultrasonic devices: not effective. Sticky deterrents: limited efficacy.
Toxicants
None are registered.
Trapping
Available, but unnecessarily complicated compared to exclusion and bat-proofing.
Other Methods
Sanitation and cleanup. Artificial roosts.
Removal of Occasional Bat intruders
When no bite or contact has occurred, help the bat escape (otherwise submit it for rabies testing).
Conservation and Public Education
Information itself functions as a management technique.
ACKNOWLEDGEMENTS
The above information was adapted from PREVENTION AND CONTROL OF WILDLIFE DAMAGE with permission of the editors, Scott E. Hygnstrom, Robert M. Timm, and Gary E. Larson (Cooperative Extension Division, Institute of Agriculture and Natural Resources University of Nebraska-Lincoln, United States Department of Agriculture Animal and Plant Health Inspection Service, Animal Damage Control, Great Plains Agricultural Council Wildlife Committee).
To learn more about Critter Control's animal control and animal removal services, visit Our Services.
For more information on Critter Control franchises, visit Franchise Opportunities.
Interested in joining the Critter Control team? Visit Employment Opportunities for more information.
