Boxelder bugs are common almost every year, but can be particularly prevalent in hot, dry years.
Boxelder bugs are 1/2-inch long dark brown or black insects with conspicuous red markings on their wings. Boxelder bugs have two generations per year. The first generations adult stage is in late June to early July and the second generation matures to adults in early fall around September. This is the generation that commonly comes to houses.
During the summer, these bugs live on boxelder trees, where they feed on seeds found on the tree and on the ground. When cool fall weather arrives, they migrate to buildings for protection. They cluster on the sides of the house.
They crawl into cracks and crevices and eventually get into the walls of houses. On warm days in winter, they can be found, often in large numbers, on the south and west sides of the house in the sun. They may also move into the house interior at the same time.
During the fall and winter they can be annoying in the house. Boxelder bugs do not feed on food or clothing nor reproduce in the house. They may spot curtains and wallpaper with their fecal material. Also, they will leave a red or purple stain if smashed.
If found indoors, remove by vacuuming. Remember not to crush them, or they will leave a red stain. Caulk all cracks and crevices to reduce their chances of entering the home. They may still enter through doorways. Eliminating seed-bearing boxelder trees may help reduce the boxelder bug problem.
Although boxelder bugs are primarily a household insect of little importance to landscape professionals, they are commonly found in masses on the trunks and at the bases of boxelder and other maples. They are effectively killed on contact with insecticidal soap spray both on tree trunks and outside building walls. Because insecticidal soap has little residual activity, spraying may be needed every other day or even every day. Boxelder bugs are not effectively controlled by insecticide residues.