INTRODUCTION:
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.
RECOGNITION:
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.
SIMILAR
GROUPS:
(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.
REPRESENTATIVE
SPECIES:
- 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 further north.
BIOLOGY:
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 13-38 years.
Bats 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.
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 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.
Second, 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.
HABITS:
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, 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.
CONTROL:
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.
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 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.
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.
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.
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