A: It sounds as though you are describing cluster flies. They are parasites in earthworms during the summer. In fall, they fly to buildings to seek any small spaces or cracks by which they can get inside for the winter.

They often find their way into wall voids and other cavities, particularly on the south and west sides of structures, where it's warmest. Eventually they can emerge into homes through small spaces, such as around light fixtures.

There are two steps to take when trying to keep fall nuisance invaders out:

—Seal as many potential entry spaces as possible around the entire building. Check especially around windows, doors and fascia boards. Examine areas where different materials meet, such as brick and wood. Also be sure to inspect areas where utility lines enter homes. You can't make a home completely "insect-proof," but sealing cracks and spaces will minimize the number of cluster flies that get inside.

—Consider supplementing these efforts with an insecticide barrier around the outside of your home. Again, concentrate your efforts around windows and doors. Use an insecticide labeled for the exterior of buildings or hire an experienced pest management company for the job.

—Jeff Hahn, entomologist, University of Minnesota Extension

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CLEANING JUGS

Q: I purchase filtered drinking water in plastic gallon jugs (like milk jugs) from a local grocery store, where they are refilled. How often and how should the jugs be cleaned? For example, should I use dishwashing liquid and then rinse out the jug thoroughly?

A: Cleaning before every fill-up makes sense. Simply use dishwashing detergent and hot water. Because antibacterial cleaners are so heavily promoted, it's easy to forget that cleaning with detergent and water is very effective.