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You may notice that wasps (usually paper wasps; occasionally yellow jackets) are attracted to the sunny sides of brick school, office, and apartment buildings in early autumn. The reason for this phenomenon is that, as the weather gets cooler in fall, wasp nests are abandoned by their inhabitants. Male wasps, whose only purpose in life is to inseminate females, fly around for a while and eventually die; females look for a sheltered, sun-warmed place in which to spend the winter. These fertilized females (next year's queen wasps) might seek refuge in a naturally occurring place such as a rock crevice or a tree hole; or they might take cover in something man-made, such as a building.

To a female wasp looking for winter shelter, a brick building looks very much like the sort of rock formation it might use for winter cover in its natural setting. The wasp will investigate it, looking for crevices it can crawl into. In this way, wasps will try to enter open windows; cracks in masonry; the gap under roof flashing; or any other entryways they can find. Those that do manage to get inside will eventually settle down for the winter in false ceilings, voids of cement wall blocks, or in the space around window frames. Before they do settle down, they may create a nuisance and frighten people by buzzing around inside the building.

Such wasps are not aggressive, but they may sting if disturbed.

The good news is that this problem does not persist long. It will only last from the onset of cool nights until the first frost - perhaps three or four weeks.

Control The best way to control this problem is to keep windows closed during the few weeks when wasps are seen on the sunny side of the building. Windows that are going to be left open for ventilation should be fitted with tight-fitting screens.

All other openings wasps might use to gain entry to the building should be plugged with caulk, concrete, or copper wool - these include openings for utility lines, cracks, and gaps around door and window frames.

Any wasps that do manage to get inside can simply be swatted with a fly swatter or a rolled-up magazine; picked up with a vacuum cleaner; or carefully shooed back outside.