Freshly laid eggs are straw yellow and turn red as the embryo develops inside. First instar nymphs are approximately 1.3 mm in length, wingless (with black wing pads) and have bright red abdomens. The legs and antennae are black. The nymphs become darker red as they mature through the five nymphal instars. The brownish-black adults are about 12 mm long and somewhat flattened on the top (Fig. 1). Three longitudinal stripes on the thorax and the margins of the basal half of the wings are reddish orange. The adult’s abdomen is also reddish orange.

With the approach of fall, this species congregates in large numbers on the south side of trees, buildings, and rocks exposed to the sun (Fig. 2). It is during this period that homeowners become aware of the insects. Adult boxelder bugs will frequently attempt to enter cracks and crevices in the walls, in an attempt to secure a protected, over-wintering site, occasionally finding their way into the living areas of homes. In late April to early May, the bugs emerge from hibernation about the time buds on boxelder trees begin opening. They fly back to host trees where they remain active over the growing season. In spring soon after finding host trees, females lay eggs in crevices in the bark of the trees. Eggs hatch in 10 to 14 days into nymphs. Nymphs feed on foliage and seeds by inserting their piercing-sucking mouthparts into these tissues. They continue feeding until they mature into adults.  Depending on weather conditions, one to two generations may be produced each year