Boxelder Bugs

Boxelder bugs found primarily on boxelder trees, as well as maple and ash trees. The adults are about 12½mm (½ in) long with a dark brown or black coloration, relieved by red wing veins and markings on the abdomen. Nymphs are bright red.

These highly specialized insects feed almost exclusively on the seeds of Acer species. Although they may occasionally pierce plant tissues while feeding, they are not known to cause significant damage and are not considered to be agricultural pests.

They may form huge colorful aggregations while sunning themselves in areas near their host plant (e.g. rocks, shrubs, trees, and man-made structures). However, their presence can frighten and annoy people, thus they are considered nuisance pests. This is especially a problem during the cooler months, where they sometimes invade houses and other man-made structures seeking warmth or a safe place to overwinter. They remain inactive inside the walls (and behind siding) while the weather is cool, without doing any damage to the building.

When the heating systems revive them, some may falsely perceive it to be springtime and enter inhabited parts of the building in search of Acer or seeds, and water. In the spring, the bugs leave their winter hibernation locations to feed and lay eggs on maple or ash trees; aggregations may be seen during this time and well into summer and early fall, depending on the temperature.