Box elder bugs (Leptocoris trivittatus) are about half an inch long and are black with red-orange stripes on their backs. They prefer female box elder trees (Acer negundo) as host plants on which they spend the warm summer months. They also live on other trees, including silver maple and green ash. The bugs breed in summer and both adults and nymphs suck sap from leaves, twigs and seeds of the host tree. Their feeding habits are not usually harmful to the host plant. Emerging from nearly microscopic eggs laid on leaves, the immature insects or nymphs are covered with a rigid shell. As the insects grow, they must shed or molt their outer skin layer. The insect is soft bodied immediately after molting, but within a few hours, the skin hardens and begins to take on color. The box elder bug undergoes five such molts before reaching adulthood.
Box elder bugs do not sting or bite. In large numbers, however, they can be a nuisance and when crushed they emit a foul odor and their body fluids can stain clothing or other material. In the fall, the bugs congregate on the south or west sides of house walls and foundations to spend the winter. They are particularly fond of hiding in cracks and small openings or under siding or wood framing of buildings. In the spring, they come out of hiding and move back to the host trees to resume their life cycle.
Spraying the bugs with insecticides is not usually warranted. Sealing or caulking cracks and openings around the exterior of buildings makes it more difficult for box elder bugs to congregate and hide.