Common northwest pests: Boxelder Bugs

(Leptocoris trivittatus) and (L. rubrolineatus)

Boxelder bugs are familiar insects to most people. Typically, these bugs become a nuisance during the fall and early spring. They are generally not noticed during summer, but often can become an issue when they try to move into homes during fall as they search for overwintering sites. Boxelder bugs seek shelter in protected places. Typical shelter areas include cracks or crevices in walls, doors, under windows and around foundations. The bugs particularly favor south and west exposures.

Adult boxelder bugs are about 1/2-inch long, black with orange or red markings, including three stripes on the prothorax, the area right behind the head. Their wings lay flat over their bodies, overlapping each other to form an X as shown in the photo. The immature nymphs are 1/16th-inch long and bright red when they first hatch. As they grow older and become larger, they are red and black. You can potentially see all stages at any given time during the summer.

Boxelder bugs are primarily a nuisance because they enter homes and other buildings, often in large numbers. Fortunately, they do not bite people and are essentially harmless to property. When abundant, they can stain walls, curtains, and other surfaces with their excrement. Occasionally some may seek moisture and may be found around houseplants, although they rarely attack them. In the few cases when they do feed, boxelder bugs are very unlikely to injure indoor plants.

Here are some tips if boxelder bugs sneak into your dwellings:

  • Caulk or seal all cracks and spaces found in your foundation, siding, windows, doors and other entry points

  • Exterior insecticide treatments

  • Soap mixtures

  • Call pest control services

  • Vacuum up boxelder bugs

Lastly, remember boxelder bugs are not able to survive more than a few days indoors and are essentially harmless. So check now, make sure your house is sealed before the boxelder population explosion hits!

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