Boxelder bugs are black plant bugs and are named for their primary host, the boxelder tree. It is found primarily on boxelder trees, as well as maple and ash trees. Box elder bugs are black in color and have red lines along the thorax sides. They are often found in homes and on the sunny exterior sides of buildings. Depending on their location, boxelder bugs breed once, twice, or three times yearly. Boxelder bugs breed during the summer and early fall seasons. Boxelder bugs do not reproduce inside homes, but find their way inside through windows, doors, ceiling lights, soffit and dryer vents, outdoor faucets, and along siding.

A bigger nuisance to homeowners, they seek and enter houses in colonies of hundreds, even thousands of insects as cold weather approaches, congregating in walls and warm basements, making themselves at home all through winter and occasionally emerging into kitchens, living rooms, bed rooms and other human-inhabited spaces. Boxelder bugs, though mostly scentless, give off a pungent odor when disturbed or crushed. Boxelder bugs are not harmful to humans or pets. They do not bite or sting; however, if you squash them on your drapes or wall, they will stain.

In late summer and autumn, then they gather in groups much like swarms of bees on the sun-facing, preferably white side of homes and garages where their sheer numbers will discolor the building’s side if allowed to stay.