Boxelder bugs can make a nuisance of themselves by gathering around the house in large numbers. They usually do this in the autumn in preparation to move into protected areas to over-winter. While they do not cause physical damage to the house, they may stain walls and curtains with brown fecal matter.

Boxelder bugs (Leptocoris trivittatus) are flat insects about ½ inch long, dark brown to black in color with three red stripes behind their head. Their lifecycle goes like this: Adults over-winter in cracks and crevices in walls, rock piles, tree holes, and other protected places. In the spring, the females emerge and lay eggs in crevices of tree bark and other objects near host plants. Eggs hatch in 14 days, with nymphs appearing about the same time new tree leaves develop. In July, new adults lay eggs that result in a second generation by early autumn.

The bugs feed primarily on boxelder trees by sucking sap from the leaves, tender twigs, and developing seeds. They also sometimes feed on maple, plum, cherry, apple, peach, and grapes, causing some scarring or dimpling of the fruits.

Boxelder bugs seldom develop into nuisance populations unless they can feed on seed-bearing boxelder trees. If you’re having trouble with the bugs, chances are you have boxelder trees nearby. Removal of these trees should eliminate high populations. Other preventive actions involve making your house tighter, especially around doors and windows. Repair any holes where the bugs can enter. Eliminate potential hiding places such as piles of boards, rocks, leaves, grass, and other debris close to the house.

Controlling the bugs themselves mostly involves using insecticides. To prevent potentially large populations in the autumn, spray boxelder trees near the home with an approved pesticide (always follow label directions). In the Fall when they gather on sidewalks and walls, treat the area they are occupying with the same insecticides. A non-chemical control method involves the liberal use of a vacuum cleaner. For more information on controlling problem bugs, contact your County Extension Agent.