Species

While bats are generally beneficial, predating insects and pollinating night-blooming flowers, they sometimes may need to be removed from human dwellings. The little brown bat (Myotis lucifugus) is common throughout North America and the species most frequently found in buildings. Another common species is the big brown bat or house bat (Eptesicus fuscus).

There are many different species of bats, varying greatly depending on geographical location. For identification help related to bats found in the northwest, see The Guide by Bats Northwest for a useful pictorial guide.

More than 15 bat species may be seen flying around Washington and Oregon, from the tiny 2.5 inch-long Western pipistrelle to the 17 inch-long hoary bat. However, the few frequently seen around human habitat apart from the little and big brown bats include:

• Yuma myotis (Myotis yumanensis), which is about 8 inches long and light brown with white markings.
• Pallid bat (Antrozous pallidus), which is about 13 inches long, light yellow on top with pale underpants.
• California myotis (Myotis californicus), which is about 3 inches long and has dull dark-brown fur.

Host/Site

The brown bats that inhabit buildings usually favor attics, barns, brick houses, porches, or any other location that provides a suitable roost. Bats cause damage when they drop their fecal matter, attracting roaches, mites and other pests. In addition, they can carry diseases transferable to humans such as rabies and histoplasmosis. As histoplasmosis may be contracted through the inhalation of bat guano, always wear a tight-fitting respirator if you are cleaning or harvesting this fecal matter.

Identification

Appearance
Bats vary in size, color, and other distinguishing characteristics based on species. Generally speaking, most bats in the Pacific Northwest range in size from 3-18 inches with light to dark brown fur.

Indicators
Bats are often identified by their droppings, acrid and musty smelling, or by their high pitched sounds that they emit.

Life Cycle

Bats mate in the late fall and winter, with the young then being born between April and July. The female normally only gives birth to one baby per litter, although some species may produce up to four per litter. Brown bats hibernate when the weather turns cold. Many bats can live for up to 10 years.

Natural Enemies

Bats are most susceptible to predation in the early evening as they are leaving their roosts, especially by birds of prey such as hawk. In addition, other bat predators include other birds of prey, many carnivores,snakes, and other bats. Nematodes, flat worms, and various arthropods are all know to parasitize bats.

Monitoring

Look for fecal droppings or brown stains from urine that become visible on the outside of buildings, particularly on eaves and entry/exit holes, this is a sign that there is a bat infestation. A strong musky and acrid odor from their feces. This fecal matter can then attract unwanted pests and parasites to a building. In addition, Bats rarely attack humans, so it is dogs and cats that stand the greatest chance of contracting rabies from an infected bat. This can be prevented by having pets vaccinated against the disease.

Action Threshold

The bat is a vector for many diseases and pathogens including rabies, severe acute respiratory syndrome (SARS), Henipavirus (ie. Nipah virus and Hendra virus), histoplasmosis, and possibly ebola virus. Because of the potential danger to human health presented by a bat infestation, even one bat in the home should be a cause for concern and warrants control measures.

Physical/Mechanical Controls

First, if there is any possibility that the bat has come into contact with a human in the house, the bat should be captured and tested for rabies. You can call your local animal control department and tell them that there is a possible exposure to rabies.

If there has been no contact, the bat may be physically removed from the house by closing all doors and confining the bat to one room. Towels may be placed under doors to seal off cracks. Open all doors and windows to the outside, as the bat will eventually migrate toward the fresh air. Keep an eye on the bat but remain still in order not to frighten it until it has left the room, which may take up to an hour.

To prevent bats from entering a house in the first place, a number of indirect strategies should be applied. Wherever possible, natural bat roosts should be preserved. If bats are living in a building where they are not wanted, shifting them to an artificial roost such as a bat house should be considered. Also, houses should be designed initially to exclude bats from entering. All openings to the outside should be sealed, especially under eaves or where electrical wires, pipes, or chimneys extend to the outside.

The Washington State Department of Fish and Wildlife has extensive information on ways to seal your home or building off to prevent bats from entering. Visit their site for detailed explanations of these preventive measures.

Biological Controls

See Natural Enemies

Chemical Controls

Due to bats beneficial qualities such as feeding on insect pests and pollinating plants chemical controls that may kill bats are not suggested.

References

Link, Russell. Living with Wildlife in the Pacific Northwest. Seattle: University of Washington Press, 2007.
28 July 2008. < http://wdfw.wa.gov/wlm/living/bats.htm>.

Myers, Phil, and Matthew Wund. "ADW: Chiroptera: Information." 2005. University of Michigan Museum of Zoology.
29 July 2008. <http://animaldiversity.ummz.umich.edu/site/accounts/information/Chiroptera.html>.