The boxelder bug is a common and well-known insect in Iowa that has been particularly abundant in the past two years. During the summer months, boxelder bugs live, feed and reproduce on trees (including boxelders, maples, ash and other shade trees) and shrubs. They feed on sap from their host plants but do not cause significant damage. Boxelder bugs become nuisance pests in the fall when they leave the plants to find hiding places for the winter. During their random search, they will congregate in the sunshine on the south sides of buildings, trees and rocks. From there they stray into houses through cracks in the foundation and siding, gaps along windows and doors, and other small openings. Boxelder bugs within walls or attics remain inactive as long as they stay cold. Bugs warmed by heat from the furnace or the sun will be active during the winter. Boxelder bugs that successfully survive the winter appear in the spring and try to return to trees to lay eggs. Boxelder bugs do not reproduce indoors. Those inside the house are harmless as they do not damage the house, its furnishings or occupants. As you know, however, they can be a considerable nuisance.
Boxelder bug populations vary from year to year and place to place, depending on weather (especially temperature and rainfall during May through July). There is no easy way to determine when and where boxelder bugs will be a problem until the problem starts. By then it may be too late for effective treatment. Boxelder bugs can be controlled on the trees in mid-summer with yard and garden insecticides such as diazinon, Orthene and Sevin. The limited effectiveness of this treatment and the difficulty of spraying large trees makes tree spraying impractical.
The best deterrence against boxelder bugs and similar invaders (e.g., crickets, attic flies and elm leaf beetles) is to prevent entry by caulking and sealing possible entry sites (cracks and gaps). A lawn and garden insecticide (such as Sevin, diazinon or Dursban) or soapy water spray can be used on masses of boxelder bugs seen on and along the foundation in the fall. A soapy water spray made with 5 tablespoons of liquid detergent per gallon of water works effectively on boxelder bugs sprayed directly, but it has no residual activity. Soapy water sprays will have to be repeated frequently. Reducing the number outdoors should limit the number that will get into the house.
Unfortunately, there is no easy cure for eliminating boxelder bugs already inside the house. They are generally not killed by the aerosol household insecticide products, and the residual insecticides such as "ant and roach killer" are not of much benefit. A sure control for boxelder bugs already in the house is to remove them as they appear, by vacuuming, sweeping or picking them up and discarding.
This article originally appeared in the March 17, 1995 issue, p. 25.