The Box Elder Bug is about 1/2 inch long and 1/3 as wide. It is black with three red lines on the thorax, a red line along each side, and a red line on each wing. The wings lie flat on the back when at rest. The young nymphs are red and gray. The population of bugs may number into the thousands.
The adults search for a place over winter which brings them into houses where they hide in small cracks and crevices in walls, door and window casings, attics, and around the foundation. During warm days in winter and early spring they come out and scatter through the house. They are primarily a nuisance as they crawl or fly about in the rooms.
Box elder bugs normally feed on the leaves, flowers, and seed pods of the box elder tree or silver maple tree. Large numbers of box elder bugs are usually on the female, or pod-bearing, tree.
The adult bugs lay eggs in the spring and the nymphs emerge in a few days. The nymphs are small and show more red than adults. These nymphs develop into adults during the summer, then mate and lay eggs which hatch into the nymphs of the second generation. Activity of nearly fully grown nymphs are noticed in August and September when they gather in large numbers on the trunks of box elder trees.
The box elder bug becomes a pest in many houses each year during fall and spring. They do no damage by feeding, but their excrement spots on household objects are difficult to remove. One myth concerning the Box Elders, they are tree killers, when in fact they cause very little damage to trees.