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Some bats are not at all averse to living in buildings and even homes. The most frequent unpleasant human encounter with bats is their uninvited appearance in houses, usually entering through unscreened windows or chimneys. The simplest solution to this predicament is to open all windows and doors to allow the bat to exit unaided. If it is dark outside, bright lights inside will hasten the bat's exit; a bat is doubtless as uncomfortable as a person under these conditions.

If noises in the attic or chimney are indeed coming from bats and not mice, squirrels or birds, the best long-term solution is exclusion. In Colorado, this should be done in the winter, when bats are hibernating elsewhere. Most problems with bats occur in summer, in fact, usually just as the inexperienced juveniles begin to fly, so it takes some patience to wait until fall to exclude them. Patience pays off, however, as attempts to exclude bats in summer almost invariably lead to entrapment of individuals, especially the young, starvation and death. Most colonies that become a nuisance to people are maternity roosts, where females gather to raise the young. This kind of colony usually is of short duration, lasting only two or three months, from June to mid- or late August. Waiting an extra few weeks before excluding the colony can save dozens -- if not hundreds -- of bats from certain death.

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Bat transmitted rabies is not epidemic anywhere. Fewer than 20 human deaths from bat-transmitted rabies have been documented in the past 40 years. In North American, deaths from bat transmitted rabies are a small fraction of those from rabies transmitted by domestic dogs or cats. In fact bee stings, lightning, and power mower accidents are far more serious risks to Americans than bats.  

In addition, because exclusion of maternity colonies from historical roost sites is particularly harmful to bat populations, an alternative structure should be provided for the bats when they return the following spring. Remember, the excluded bats may have been using your house as a maternity roost for a century or more, and having them around to control insects is well worth the price of a few bat houses. The bat houses should be erected near the original entrance to the attic. This will assure that the bats find their new home. These simple procedures can allow for harmony between humans and bats. Bat Conservation International has published a brief but valuable guide to bat houses.

To exclude bats from a structure, all holes must be located and sealed with siding, screen or caulking. Bats are smaller than they may seem, and they can usually wriggle their body in anywhere their head will fit, so cracks as narrow as a pencil -- about one-quarter inch -- will accommodate even medium-sized bats. Some preferred entrances are in older frame structures, where boards are loose, warped or shrunk. Bats may also enter the house through loose vents, eaves, cracks under loose flashing, spaces around water pipes, electrical service, beneath corrugated roofing, and around ill-fitting doors and windows.

Chemical repellents sometimes used against bats are unnecessary, ineffective and poisonous to other animals, including humans. Naphthalene -- the only chemical registered by the Environmental Protection Agency (EPA) for indoor bat roosts -- has been spread on attic floors or suspended in mesh bags from the ceiling. Although chlorophacinone, an anticoagulant toxin, is registered for bat control in some states, it is not recommended by the EPA or U.S. Fish and Wildlife Service. It is extremely toxic and probably presents a greater threat to human health than do bats. Physical repellents tried with varying success include floodlight illumination in roosts, drafts from electric fans and high-frequency sound recordings.

Bats are often thought to be important carriers of disease. This is far from true. In general, bats are very clean mammals that harbor few diseases. Rabies is the most significant public health hazard associated with bats, but its impact has been greatly exaggerated. There have been isolated instances of rabid bats biting people in Colorado, but prompt medical treatment has prevented the disease from being fatal.

According to Dr. Merlin Tuttle, fewer than 0.5 percent of bats ever contract rabies, and fewer than 1 percent of those attack other animals. Work by Dr. Denny Constantine, a public health veterinarian, suggests than only about one in a thousand bats may be incubating rabies, and those that do soon are paralyzed and die. In addition, major studies carried out from Georgia to Canada concluded that rabies in other wildlife species is least common where bats are most common. If bats were important reservoirs of rabies, transmitting the disease to other species as once thought, the opposite would have been true.

Although most bats do not carry rabies, grounded or easily handled bats probably are sick or injured and should be avoided by untrained people, as should all wild animals.

For more informations, see the DOW's Living with Wildlife: Bats and Rabies page.

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