The boxelder bug sucks the sap from the leaves and flowers of host plants but does little damage, and in most years is of little significance to the host. Large populations may build up so that they become a nuisance in and around homes and yards. These insects congregate on the sunny side of trees, houses and other structures. The boxelder bug survives the winter by hibernating under loose bark, in houses, under siding or cracks in concrete, window and doorsills. During warm winter and spring days, they become active, moving from their hiding places into living spaces. Boxelder bugs do not cause damage to food, fabrics or buildings, nor do they vector human disease, but may stain some items with their excrement.

Description - Adult boxelder bugs are flat-backed, elongate, narrow, about 14 mm long, 8 mm wide and dark brownish-black with three lengthwise red stripes on the pronotum (area behind the head). The head is black with a reddish-orange beak (proboscus). The antennae are black, thin and about half as long as the body. The wings are thick and leathery at the base and membranous at the tip. There are red veins in the wings and at the abdomen is bright red under the wings. The nymphs resemble the adults in shape except that they are smaller, more rounded and wingless. Eggs are dark reddish-brown and are usually found on the leaves of the host tree.

Distribution and Host Plants - The boxelder bug is found throughout the United States and Canada wherever boxelder trees grow. Boxelder bugs feed primarily on the leaves, flowers and seeds of female boxelder trees and to a lesser extent on the male trees. However, during periods of high population they also feed on other trees and shrubs and some garden plants.

Damage - Boxelder bug does very little feeding damage to its host. However this insect becomes a nuisance when large numbers congregate on structures. Occasional staining of fabrics by insect's excrement has been reported.

Life History - Adult and large nymph boxelder bugs begin to congregate in large numbers in early October primarily on the bark of boxelder trees and then begin to migrate to overwintering sites. Only full-grown adults overwinter, moving to hibernation sites by crawling or flying. Boxelder bug adults may crawl from a nearby tree or fly up to two miles to find a suitable site. On warm days during winter and early spring, the overwintering adults sometimes appear on light-painted surfaces outdoors and on the west sides of structures, resting in the sun. Overwintering adults leave their hibernation sites with the onset of warm weather in late March. Female boxelder bugs begin laying eggs in the crevices of tree bark in late April though early May. Eggs hatch in about 11 to 19 days, with bright-red nymphs appearing about the same time new leaves develop. There are five nymphal instars. Each instar becomes progressively darker red. By July, nymphs mature into adults that lay eggs that result in a second generation by early autumn.

Control - Since boxelder bugs feed primarily on female (pistillate) boxelder trees, removal of these trees, especially around the house, would reduce nuisance populations. Eliminate hiding places such as piles of wood, rock and debris near buildings. Seal cracks in foundations, siding windows and doors. For specific chemical controls, see the current PA Department of Agriculture recommendation or contact the nearest Penn State Extension Office.