Adult boxelder bugs are about 1/2-inch long, black with orange or red markings, including three stripes on the prothorax, the area right behind the head. Their wings lay flat over their bodies, overlapping each other to form an ‘X’. The immature nymphs are 1/16th-inch long and bright red when they first hatch. As they grow older and become larger, they are red and black.
Boxelder bugs are primarily a nuisance pest, annoying residents by crawling on exteriors and inside dwellings on warm fall and winter days. They also may stain draperies and other light-colored surfaces and produce an unpleasant odor when crushed, but these are not major problems. They do not reproduce during this period. They may attempt to feed on house plants but do not cause any damage. On rare occasions, they have been reported to bite humans.
Boxelder bugs feed on a variety of plants, but their favorite food is boxelder seed pods, which are found only on the female boxelder tree, and occasionally maple seeds. These bugs seldom develop in sufficient numbers to be a nuisance unless a female boxelder tree is in the neighborhood.
During the autumn months, adult and large nymph boxelder bugs congregate in large numbers, primarily on the bark of boxelder trees, and then begin migrating to a place conducive to overwintering. Only full-grown adults overwinter, moving to hibernation sites either by crawling or flying. They may crawl from a nearby tree or fly as many as two miles to find shelter. These bugs hide in cracks and crevices in walls, in door and window casings, around foundations, in stone piles, in tree holes and in other protected places. On warm days during winter and early spring, they sometimes reappear on light-painted surfaces outdoors on the south and west sides of the house, resting in the sun. Overwintering adults leave their hibernating quarters with the coming of warm weather, and females begin laying eggs in crevices of tree bark, stones, leaves, grasses and on other objects near host plants. Eggs hatch in 11 to 19 days, with bright-red 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.
Since boxelder bugs feed and reproduce primarily on pistillate (female) boxelder trees, removal of these trees, especially around the house, would eliminate nuisance populations. Eliminate potential hiding places such as piles of boards, rocks, leaves, grass and other debris close to the house. Rake leaves and grass away from the foundation in a six- to ten-foot-wide strip, especially on the south and west sides of the structure. Be sure to caulk and close openings where boxelder bugs can enter the house, such as around light fixtures, doors and windows, unscreened vents, holes in walls and foundations, around utility pipes or conduits, air conditioners, etc.