Boxelder Bug (Boisea Trivittata)

They’re everywhere! In some parts of Minnesota, a sure sign of impending winter is a convergence of boxelder bugs on the sunny side of buildings. Where did they come from, and why are they trying to get into your house?

Appearance. Adult boxelder bugs are flat and elongated, about the length of a grain of wild rice. They are mostly dark brown with red-orange borders along their sides and at the tail end of their wings. They have red eyes, conspicuous antennae with fuzzy ends, and six long legs. Females are a little larger than males. Newly hatched boxelder bugs, known as nymphs, are about the size of a mustard seed. They are bright red and lack wings. As they grow and molt, they sprout wings and take on more brown coloration.

Range and Habitat. Boxelder bugs, native to Minnesota, live throughout the state. In the north they may reproduce only once a year, so populations may be lower there. Boxelder bugs like to hang out in deciduous trees—not only boxelders, but also maples and ashes.

Life Cycle. Adult boxelder bugs winter in a dormant state. They emerge in early spring and spend a couple of weeks fattening up before they mate. After mating, the females lay pencil-point-size eggs in batches of 10 or so in crevices in tree bark or in leaves or other organic material on the ground. The light-colored eggs turn reddish brown. After about two weeks, bright red wingless nymphs emerge. The young molt five times, growing a little larger and looking a little more like the adults each time. They mature in seven to 10 weeks, depending on food availability and weather. Nymphs suck juice from plant leaves. Adult boxelder beetles also eat leaves, flowers, twigs, and other plant parts. Sometimes they eat each other or dead insects. Boxelder bugs can be part of the diet of rodents, birds, spiders, and other insects. However, a foul odor they give off when crushed likely serves to deter predators.

Fall Flurry. In the fall, boxelder bugs seek sheltered places to hibernate. Some secret themselves in cracks and crannies on the outside of buildings. If there are no buildings around, they may tuck themselves into leaf piles. They are attracted to warmth, so if they find a building with a southern exposure, they gather in large numbers in search of a place to shelter for the cold season. Others find their way inside and become dormant until late winter.

Human Impacts. Boxelder bugs don’t bite or sting, but their sheer presence can be a nuisance. Populations tend to boom when summers are hot and dry, leading to large numbers congregating in the fall in search of cold-season shelter. Sealing cracks in windows and doors can help prevent them from entering and wintering inside human homes.