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"
(5.6-18.8 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 9) 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.
(1) 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. (2)
Birds (class Aces) with body covered with feathers and a horny
bill lacking teeth.
1. 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, wingspread 11 3/8-12
13/16" (29-32.5 cm), and weight 3/8-1/2 oz (11-14 g);
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
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 23 days. Young are
normally left hanging in the roost, but may be carried by
the female. They are weaned at about 1 month. 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 20 years, and the Mexican free-tailed bat
have relatively poor vision and instead rely on echolocation
(similar to sonar) to avoid objects and find prey. 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.
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 CDC (Centers for
Disease Control) 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.
accumulations of bat droppings in attics or soil create conditions
suitable for the growth of Histoplasmosis capsulatum, a fungus
which 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
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,
leafhoppers, 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.
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.
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 comers 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
facie boards meet, under facie boards, and other openings
due to deterioration.
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.
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 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 and seal these last entry/exit holes.
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.
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.
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.
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.
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.