Boxelder bugs are a nuisance in and around homes from fall through early spring. This bug is about 1/2 inch long as an adult, black with three red lines on the thorax (the part just behind the head), a red line along each side, and a diagonal red line on each wing. The immature forms are smaller and are easily distinguished from the adults by their red abdomens and lack of wings.
These insects feed on the softer plant tissues, including leaves, flowers, and new twigs. Unless the population is exceptionally large, the damage to plants is minimal. During years when their population soars, they can damage useful shade trees.
In autumn, they can become household and hotel pests. The adult insects seek wintering hibernation locations and find their way into buildings through crevices. They remain inactive inside the walls (and behind siding) while the weather is cool.
Boxelder bugs are primarily a nuisance pest, annoying residents by crawling on exteriors and inside dwellings on warm fall and winter days. They also may stain draperies and other light-colored surfaces and produce an unpleasant odor when crushed, but these are not major problems. They do not reproduce during this period. They may attempt to feed on house plants but do not cause any damage. On rare occasions, they have been reported to bite humans.
The most permanent solution to the boxelder bug problem is the removal of female boxelder trees from a neighborhood, although this may not be practical or desirable. Because boxelder bugs usually overwinter near the trees that they feed on, the removal of one or two problem trees may help. Screening or sealing cracks or other entrances into the dwelling is important. Once boxelder bugs have entered the home, control becomes more difficult.
When the bugs begin to congregate on building exteriors, these areas (including all resting and hiding places) may be sprayed with residual insecticides.