University of Illinois Extension
Bruce Spangeberg

These articles are written to apply to the northeastern corner of Illinois. Problems and timing may not apply outside of this area.

Stateline Yard & Garden

Indoor Insect Pests in Winter

December 24, 1998

Nuisance insects crawling or flying around indoors typically are considered a summer problem, but some are actually most common during winter. Fortunately, most are only nuisances rather than permanent pests in the home.

For example, a variety of insects may be carried in on firewood. Insect borers are common in firewood, and may crawl out if the wood is allowed to warm indoors. Some might decide to fly around the room. Fortunately, these insects are more interested in decaying wood rather than the typical wood the house is made of.

If insects are crawling out of firewood, DO NOT spray the firewood with an insecticide. The best solution is to store firewood out in the cold and only bring in enough to put right into the fire. Spraying the home is seldom necessary because the insects will not take up residence.

Flies may appear on a sunny winter day, often near windows in the upper potions of the house, in particular older homes. These are usually cluster flies, a group of fly species that overwinter in structures, but do not breed in the home. Typically they will get under siding or work their way in through cracks or crevices. Once inside, cluster flies will often become active on a sunny day, usually being attracted to windows.

The best strategy for dealing with cluster flies is to prevent them from getting in. Next summer, rather than now, consider sealing cracks and openings around windows, eaves, and siding. Be sure screening exists over air intake vents. Seal off attic openings with screen or caulking. Remove the flies indoors by vacuuming. Pyrethroid sprays are another option for rooms with high infestations; be sure to read label directions.

Finally, drain flies may appear in homes. Drain flies are dark colored, somewhat slow-flying insects that turn into powder when crushed. As the name implies, they lay eggs in organic matter that may accumulated in drains or other areas of standing water. These eggs hatch into maggots that eventually become the adult drain fly. Cleaning out the drains is the best control measure. Slowly pour boiling water, rubbing alcohol, or drain cleaner into drains after cleaning out debris.



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