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Bat Infestation

Bats are nocturnal mammals found in most inhabited places throughout the world. Bat infestation in homes, especially in attics, can be a health hazard, as well as a nuisance, for homeowners.

Interesting Facts

  • Due to its high levels of phosphorous and nitrogen, guano (bat feces) is an effective fertilizer and gunpowder ingredient. Guano has been such a critical resource that in 1879, a war between Chile and Bolivia, called the Guano War, was waged over rights to the guano-rich western coastline.

  • Despite how large they appear in flight, bats are remarkably small. Some can fit through openings smaller than ½-inch wide. Even the largest bat – the golden-crowned flying-fox -- with a wingspan of up to 5 feet, may weigh as little as 3 pounds.

  • Roughly 20% of all known mammal species are species of bats.

  • Bats are the only mammals capable of sustained flight.

  • Contrary to popular belief, bats are neither rodents nor birds, and they are not blind.

Indications of a household bat infestation:

  • the accumulation of guano. Bat guano resembles rodent droppings but can be distinguished in several ways: guano tends to cluster as it piles up beneath the exit of the bats’ roost; guano often has a shiny, speckled appearance due to the ingestion of insect wings; and guano can be easily crushed into smaller fragments, while rodent droppings will not. Of course, it is not safe to touch any animal droppings with unprotected hands;

  • milky white urine stains on windows;

  • stains around entry holes, such as cracks and crevices;

  • mouse-like droppings under eaves and overhangs;

  • stains and odors caused by urine and guano;

  • noises such as squeaking, scratching and crawling in attics and walls shortly before dusk and dawn; and

  • grease and dirt. Bats often leave smears of grease and dirt from their coats on the entry point to their roost.

Bats and Disease


Due to their high mobility and social behavior, bats are often hosts for diseases, such as rabies. Rabies is perhaps the most serious disease transmitted by bats in North America. Most of the human rabies cases in the United States have been caused by the rabies virus from bats. Awareness of the facts about bats and rabies can help homeowners protect themselves, their families, and their pets. Rabies is a virus that affects the nervous system of humans and other mammals. Once symptoms of the disease develop, it is almost always fatal. Humans contract rabies from animal bites. Some bats have teeth so sharp that a sleeping person may not realize that they have been bitten. It is recommended that those waking up with bats in the bedroom undergo a series of preventative (and sometimes painful and expensive) rabies inoculations. The alternative is to capture the bats (without being bitten) and take them to a laboratory for testing. Indications that a bat has rabies:
  • The bat is in an unusual place, such as a bedroom or in the lawn. Healthy bats do not rest on the ground.

  • The bat is approachable. Healthy bats are scared of humans and will flee long before they can be approached.

  • The bat is active during the day.

  • The bat appears unable to fly.

For these reasons, rabid bats are often most likely to come into contact with humans.


This respiratory disease, caused by the fungus Histoplasma capsulatum, is transmitted through the inhalation of fungal spores found in bat guano and bird droppings. Although generally not fatal, histoplasmosis can cause flu-like symptoms. For individuals with compromised immune systems, such as those with AIDS, histoplasmosis can be fatal.

Bat Removal

The following instructions for bat removal can be passed on from InterNACHI inspectors to their clients:

  • The entry point for the bats should be identified. Holes as small a human thumb are large enough for some bats to squeeze through. The homeowner can seal off most of these holes with caulk, leaving one hole intact for resident bats to exit at night.

  • The homeowner can then plug this hole at night so that bats cannot return to the house. Alternatively, the homeowner can install a one-way “check-valve” from wire mesh that will allow bats to exit the house but not allow them to return.

  • “Bat houses,” which can be constructed or purchased, can be placed next to the house during bat removal to provide bats with an attractive alternative to the house.

Note: Bat removal should not take place during the summer (in North America). Baby bats that are unable to fly will not be able to leave the house during the summer months and they will starve to death if adults are not permitted to enter the home. Bat removal during the summer is inhumane and will result in the additional problems posed by decomposing bat carcasses.

In summary, bats can transmit dangerous diseases to humans, and inspectors and homeowners should be wary of bat infestations.

Used with permission of InterNACHI

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