Bats are nocturnal, flying mammals which inhabit dark, secluded places. In western cultures, they have traditionally been associated with witchcraft, sorcery, haunted houses, cemeteries, and evil. For centuries, they have been the subject of fables, folklore, and myths. Unfortunately, many myths regarding their lives still exist and serve as a basis for unfounded fear. Bats are of medical concern because a very small percentage are infected with rabies, and old droppings may harbor the fungal organism that causes the lung disease histoplasmosis. There are over 980 species of bats worldwide with about 40 species occurring in the United States. However, none occur in the colder areas located beyond the limit of tree growth.
Depending on the species, adults about 2 3/16-7 1/2″ (5.5-18.8 cm) in length from tip of nose to end of tail, wingspread about 6-15″ (15.2-38 cm), and weight about 1/8-2 1/8 oz (3.1-61 g) for United States species. Color tan to black. Head with very large ears. Fly on 2 wings consisting of a double membrane stretched across enlarged arm bones and elongated finger bones. Body covered with hair. With 2 pectorial teats
Note that bat species are difficult to identify, even by the experts. If assistance is needed, contact the wildlife or zoology department of a local museum or university, fish and wildlife personnel, or the local health department.
- Flying squirrels (order Rodentia) capable only of gliding and do not fly, with upper and lower pair of enlarged chisellike incisor teeth, and tail bushy, about half body length.
- Birds (class Aves) with body covered with feathers and a horny bill lacking teeth.
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- Big brown bat, Eptesicus fuscus (Beauvois); family Vespertilionidae. Adults about 4 1/8-5″ (10.6-12.6 cm) long including tail, wingspread 12-14″ (30.5-35.6 cm), and weight usually 2/5-3/5 oz (11-18 g, up to 30 g); color brown dorsally (light in deserts to dark in forests) and usually glossy, belly paler with hairs dark at base; and wings and interfemoral membrane (between leg and tail) black; no fur on wings or interfemoral membrane; tragus (leaflike structure in ear) blunt; with 32 teeth and no reduced premolar behind canine; found throughout southern Canada and United States except for southern Florida.
- Little brown bat, Myotis lucifugus (LeConte); family Vespertilionidae. Adults about 3 1/8-3 5/8″ (7.9-9.3 cm) long including tail, wingspread 8 11/16-10 5/8″ (22.2-26.9 cm), ears 1/2-5/8″ (1.2-1.6 cm), and weight 1/8-1/2 oz (3.1-14.4 g); color various shades of glossy brown, hairs on back with long glossy tips, and belly buff; ears moderately long (bent forward reach nostril) with tragus (leaflike structure in ear) short and rounded; with 38 teeth; found from middle Alaska through southern Canada to throughout the United Sates except for Florida, Texas, and southern California.
- Mexican/Brazilian free-tailed bat, Tadarida brasiliensis (Geoffroy), formerly T. mexicana; family Molossidae. Adults about 3 1/2-4 3/8″ (9-1.1 cm) long including tail, wing- spread 11 3/8-12 13/16″ (29-32.5 cm), and weight 3/8-1/2 oz (11-14g); color usually chocolate brown, varies from dark brown to dark gray above with hairs whitish at base; fur velvety and short; ears separated at base; with 32 teeth; tail extending well beyond edge of tail membrane; found throughout southern United States, in the west extending north to southern Oregon and southern Nebraska, in the east extending north to northern Louisiana, Alabama, and South Carolina, and a few scattered further north.
Females preparing to give birth either found/establish nursery or maternity colonies in locations other than their overwintering site or remain in their all-season site. Little brown bats give birth to usually 1, but occasionally 2, young during May to July. The gestation period is about 50-80 days. Young are born naked, with the eyes opening in 2-3 days. Young are normally left hanging in the roost, but may be carried by the female. They are weaned at about 1 month, but typically do not leave the roost for several weeks. Big brown bats give birth to usually 2 (east of Rocky Mountains) or 1 (in Rockies and westward) young during April to July. Mexican free-tailed bats give birth to usually 1 young during late June which is weaned in July or August. Most bats live for an average of 4-10 years; ranges include big brown to 19 years, little brown to 31+ years, and the Mexican free-tailed bat 13-38 years.
Bats have relatively poor vision and instead rely on echolocation (similar to sonar) to avoid objects find prey, and to communicate. During flight the bat emits a series of supersonic sounds (about 30-60 squeaks/sec with a pitch of 30-100,000 cycles) through its nose or mouth which bounce off objects and are picked up by its ears.
Of general concern are the medical implications of bats and their droppings. First, only a very small percentage of bats are infected with rabies, but infected bats may not show any symptoms. Rabies can be transmitted when saliva or body tissue of an infected animal comes into contact with open wounds or mucous membranes, such as those of the eyes and nose, of another animal including humans; it is not necessary to be bitten by a rabid animal to become infected. The article on rabies surveillance in the US and Puerto Rico during 2005 published in JAVMA (Journal of American Veterinary Medical Association, vol. 229, No. 12) stated that in 49 states and Puerto Rico, there were 6,417 rabies cases in nonhuman animals and 1 in humans. About 92% of the cases were in wildlife and 8% in domestic animals. Bats represented 1,408 cases or 21.9%. The CDC (Centers for Disease Control) reported that during 2000-2006, there were 19 human rabies cases reported in the United States.
The CDC recommends pre-exposure rabies immunization for people in occupations that have an increased risk of rabies exposure, especially animal handlers. Immunization consists of 3 shots given over about a 30-day period, with about 20-25% of the vaccinated people reporting some kind of reaction (not life-threatening) to the shots. Pre-exposure immunization does not eliminate the need for post-exposure treatment, but it reduces the post-exposure regimen.
Second, accumulations of bat droppings in attics or soil create conditions suitable for the growth of Histoplasmosis capsulatum, a fungus that can cause the lung disease histoplasmosis. Infection occurs by breathing spores contained in dust found in the roost. In severe cases, histoplasmosis can be fatal.
The 3 most common bats to enter structures are the 3 representative species given above, the big brown, the little brown, and the Mexican free-tailed bat. All 3 of these bats leave their roosts at dusk and return just before dawn. Usually their first stop is at a stream, pond, or lake for a drink of water and then feeding begins. Their habits can be summarized as follows:
- Big brown bat females form nursery colonies in structures in the spring while males roost elsewhere; later in the summer the sexes roost together. They commonly roost in attics and church belfries and behind shutters and loose boards on buildings. They leave their roost about dusk in a slow, fluttering flight. These bats usually feed near the ground and feed on insects, primarily on beetles but also on wasps, ants, planthoppers, leaf-hoppers, flies, moths, etc. They are capable of flight up to 40 mph (24.8 km/hr) which is the fastest reported for any bat. Big brown bats are the most common bat to hibernate in structures in Canada. However, they typically disperse relatively short distances and hibernate singly or in small groups in hollow trees, rock crevices, drainage pipes, caves, mines, and buildings. In Canada, hibernation extends only from December to April.
- Little brown bats form nursery colonies in structures in the spring. They feed on insects, especially flies and moths; 1 bat can catch 600 mosquitoes in 1 hour. They alternate feeding flights with rest periods during which they hang to digest their catch. Their flight is erratic with flight speed averaging 12.4 mph (20 km/hr), but ranging up to 21.7 mph (35 km/hr). In the north, most migrate south in the autumn with the migration covering up to 443 mi (275 km). From September/October through March/April they hibernate in irregular clusters, using mines and caves in the east. They have good homing instincts as illustrated by a return home in 3 weeks after being released 270 mi (435 km) away.
- Mexican free-tailed bats usually live in huge colonies where the young are raised. In the southeast and on the west coast they live in structures, but they live in caves from Texas to Arizona. Typically they fly at about 10-15 mph (6.2-9.3 km/hr) but can exceed 25 mph (15.5 km/hr). Sometimes they may go up to 50-150 miles (31-93 km) distant to their feeding grounds. They feed on insects, especially moths, but also ants, beetles, leafhoppers, etc. captured in the interfemoral membrane. They eat up to 1/3 their body weight each night. Those in the southeast and on the west coast hibernate but do not migrate. Most of those in Texas to Arizona migrate to Mexico for the winter, sometimes traveling over 800 mi (1,288 km). They leave in late October and return in March.
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Bats are protected by law in most states. Check with the state wildlife service for any restrictions before starting a bat management program. Some states even have regulations regarding batproofing. Typically, bats can be killed only if they have bitten or scratchd someone and the bat is needed for rabies testing purposes.
Bat management begins with 2 inspections. First, inspect at dusk to determine exit/entry points and the size of the infestation. This requires a minimum of 2 people at opposite corners to see all sides of the roof at once; roofs with wings require more people. The inspection should begin about half an hour before dusk and stop an hour after dusk; remember that bats do not fly in rainy or unseasonably cold weather. Common exit/entry points include attic louvers, roof lines where sheeting and facia boards meet, under facia boards, and other openings due to deterioration.
Second, inspect during the day to locate exterior structural deficiencies, inside roosting sites (check opposite exit/entry points, wall voids, etc., look for droppings and/or bats), access problems, and to determine equipment needed. Minimum personal protective equipment required before entering a bat roost includes a respirator with HEPA filters, coveralls, heavy leather gloves, bright flashlight, and bump cap.
Bat proofing is the control method of choice if it is practical and economical. Exclusion is the only method to keep bats out long term. The best time to bat proof is after the bats have left for hibernation in the autumn and before they return in the spring. Summertime bat proofing should only be done after mid-August to avoid trapping young; never batproof from early May to mid-August. Seal all but 1 or 2 exit/entry points and all other holes 3/8″ (9 mm) or larger. Then wait 3-4 days for the bats to adjust. Finally, seal those remaining holes some evening just after the bats leave for their night feeding. An alternate way is to install one-way bat check valves/cones in the last 1 or 2 entry/exit holes to prevent bat reentry, and then come back several days later to remove the check valves/ cones and seal these last entry/exit holes.
If there are just too many potential exit/entry points, installation of plastic bird netting should be considered. It can be cut for specific areas or draped over the entire roof area in the case of Spanish tile roofs.
The use of naphthalene flakes to repel bats only works in confined spaces, but the odor is usually objectionable and it requires repeated applications. Bright lights can help, but all dark areas must be illuminated to be effective and total control should not be expected. Ultrasonic devices have not been found to be effective for repelling bats from structures. Poisoning bats is illegal and it may result in an increase in the number of contacts with humans and pets in the vicinity.
On occasion, if 1 or 2 bats enter a structure, open the doors and windows and turn out the lights. The bats will follow the fresh air currents to the outside.
If bat control is done, be sure to ULV and/or apply an appropriately labeled residual to the roost area to help control the bat ectoparasites, such as mites and bat bugs, which will probably be present. Many of these will bite humans.
The customers should be advised of the potential health hazard that accumulated bat droppings present. These droppings can be left alone with access secured, or they can be professionally decontaminated and removed.