Hiring an exterminator or "doing it yourself" may seem like the simple, very direct solution. Consider these thoughts before attempting any exterminating:

• It is inhumane when better options exist.
• Will ultimately fail because the roost is still available for bats.
• In many states, including Pennsylvania, it is illegal to kill bats in buildings. Exclusion is the only recommended method.
• Chemicals that can kill bats are also just as hazardous to humans.
• There are no chemicals licensed for use on bats in the United States. Any company proposing to do so should have their practices questioned. In the United Kingdom, any exclusion is illegal without first consulting local officials.
• Some services will offer to catch and release bats far away, but bats have been proven to return from up to 400 miles away; a few weeks later they will be back.
• Sealing the structure while providing an alternate roost (a bat box) is the permanent solution.

Bats use human structures because the traditional roosting platforms (tree bark with exfoliating bark) are more scarce today compared with what our landscape appeared like nearly 300 years ago. A few species have adapted and even flourished where they have found proper temperatures, humidity, and crevices in certain man-made structures such as attics and steeples. As new superior construction replace the old, bats are having increasing difficulty finding even a marginal home.

This makes it important to seal the structure's entrances, which may be cracks less than 1/4'' wide. Otherwise, a new colony will surely take up residence after the old one is gone. By observing the summer evening exit, these entrances can be located. There may also be staining visible just below these entrances. Sealing should take place November-February when bats are hibernating in local caves and mines.

In some warm regions bats occupy structures throughout the year. In this case a more aggressive approach is taken to seal all entrances except the main. At that point a simple device is installed to allow bats to escape but not reenter. Structures should not be sealed in summer or early fall because flightless young may be trapped inside. Patience is required to win, as may take three seasons or more to completely bat-proof a structure. Persistent bats will use less desirable entrances once the main ones are blocked. [more on evicting]

Installing a bat box during an eviction project will improve the chances of success significantly, as bats will opt for the better available roost in face of awkward, undesirable entrances. However, bats will never completely abandon a structure for a bat house until some degree of repair work is complete.