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

Boxelder Bugs Return with Fall

October 7, 1999

With the weather cooling down and trees turning bright colors, we know fall is here. Another sign of fall for some homeowners, however, is the return of the boxelder bugs coming back as nuisances in the home.

Boxelder bugs are about 1/2 inch long and are dark brown or black with conspicuous red markings on their backs. Nymphs of the boxelder bug are small and bright red and are often misidentified as a different insect. Seeds, flowers, and leaves of the boxelder tree are their primary food source, so they spend most of the season in and around boxelder trees. They may also feed on the closely related maple, along with ash, cherry, and apple.

As it starts to get colder, boxelder bugs move to structures. They spend the winter between the walls of homes and garages and emerge again in spring to return to trees to feed and lay eggs. On warmer, sunny days, the boxelder bug may congregate in large numbers on south and west facing walls. They do not lay eggs in buildings, however. Eggs are laid on trees early in the season.

Certainly having boxelder bugs in and around the home is a major nuisance. They do not feed or reproduce, but can leave stains on fabric. Nonetheless, homeowners facing this large population of insects want to do something to reduce the numbers.

Use direct control measures to keep insects out of the home. Caulking cracks and crevices along foundations, windows, and door frames along with keeping screens in good repair will help considerably.

Another alternative for treating groups of boxelder bugs on outside walls, tree trunks, under eaves, or other areas they have gathered is to spray them with insecticidal soap. They must be sprayed directly for this treatment to work. Spraying is not suggested indoors.

As we get further into fall and some hard freezes occur, the boxelder bugs should begin to die if they cannot find shelter.


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