Boxelder Bug (Boisea trivittata)
People throughout the state of Michigan have experienced record numbers of this black and red bug for the past several years. Some folks have reported piles of them in their yards and driveways. During the summer boxelder bugs feed on the flowers and seedpods of female boxelder trees. Boxelder bugs invade our homes and other structures in the fall of the year looking for dry, protected sites (attics, wall cavities) in which to spend the winter. They can become quite numerous on the south and west sides of homes where they congregate in the warm autumn sun. In homes invaded by boxelder bugs, it is very common and likely that one will continue to see them throughout the winter and spring months. They are a nuisance but also harmless. They do not bite, lay eggs in our homes, get into our store foods, or eat our fabrics. Compared to the Asian Lady beetle, boxelder bugs are polite houseguests.
The best long-term method of controlling boxelder bugs is to prevent their entry, and if possible, the removal of any nearby female boxelder trees. Sealing exterior cracks and holes with caulk can greatly reduce the number of bugs that find their way inside walls and attics. There is very little that can be done once the bugs are inside the walls. Even aggressive and costly insecticide applications may not be effective because it is nearly impossible to treat every hidden area that may be harboring insects. Sealing cracks around electrical outlet boxes, switches and light fixtures, and around window and baseboard molding on the inside walls will help keep the bugs trapped within the walls. In older homes with double-hung windows equipped with pulleys, insects commonly enter living areas through the pulley opening. Masking tape applied over the opening will keep insects from entering through this route. A vacuum cleaner is a pretty effective method of removing the sluggish, slow moving bugs from the house. Spraying the outside walls of homes, especially the south and west facing walls, with permethrin or other insecticides registered for this use in September can also help reduce the number of insects entering homes. The spray should be applied when the first boxelder bugs are noticed congregating on outside walls.
Be sure to read and follow all instructions and safety precautions found on the label before using any pesticide.