Box elder bugs go relatively unnoticed most of the year. In fall, however, these true bugs have an annoying tendency to aggregate on people's homes. As temperatures drop, box elder bugs make their way inside houses and other structures, seeking warmth. Then they get noticed, as worried homeowners try to battle the bug invaders. Should you find box elder bugs in your house, don't panic. They're completely harmless to people or property.
Adult box elder bugs measure about 1/2 inch long. Like several other red and black true bugs, box elder bugs are flat-backed and elongate. Behind its black head, a box elder bug has three lengthwise red stripes on its pronotum; these markings are characteristic of box elder bugs. Each wing is outlined in red on the outer edge, and bears a diagonal red marking as well.
Newly hatched box elder bug nymphs are bright red, with rounded abdomens. As they molt and age, black markings start to appear. Box elder bug eggs, laid in clusters, are golden or reddish brown.
Adult box elder bugs feed on the sap of box elders, as well as other maple varieties, oaks, and ailanthus. They use piercing, sucking mouthparts to draw the sap from leaves, flowers, and seeds of these host trees. Box elder bug nymphs feed primarily on the seeds of box elder trees.
Box elder bugs undergo incomplete metamorphosis in three stages:
Egg – Females deposit clusters of eggs in bark crevices, on leaves, and on seeds of host plants in spring. Eggs hatch in 11-19 days.
Nymph – Nymphs go through five instars, changing from bright red to darker red with black markings as they molt.
Adult – By mid-summer, the box elder bugs reach adulthood. In some areas, this new population of adults may then mate and lay eggs, resulting in a second generation before fall.
Special Habits and Behaviors:
Box elder bugs aggregate in sunny places for warmth during fall. Adults overwinter in buildings, often in attics or inside walls. On sunny winter days, they may become active and cluster near windows or other warm areas of the home. Adults do not reproduce while overwintering in buildings.
Like many other true bugs, box elder bugs produce a foul odor when crushed, so the worst thing you can do is try to squash them. Indoors, they may leave fecal stains on walls and draperies.
Box elder bugs live in forests or other areas with deciduous trees, especially places where box elder trees grow.
Boisea trivittatus, also known as eastern box elder bug, lives east of the Rocky Mountains in both the U.S. and southern Canada. The similar species Boisea rubrolineatus, western box elder bug, inhabits areas west of the Rockies.
Other Common Names:
eastern box elder bug, boxelder bug, maple bug, democrat, politician bug, populist bug