While the boxelder bug can cause minor damage to its preferred host plant, the boxelder tree (Acer negundo), it is primarily a nuisance for the homeowner who finds large colonies of adults seeking places to overwinter. The boxelder bug will seek access to warm buildings through any cracks or crevices in foundations, doors, and windows, and it is their presence indoors that poses a nuisance. Although the boxelder bug neither bites humans nor spreads disease, the very act of trying to eliminate them is a major challenge.
The adult boxelder bug is oval-shaped, 3/8-5/8 inches long, and distinctively marked with three fine red lines, one down the center and one on each side of the thorax, as well as on its front wings. Its base color can be dull black to charcoal gray. At the immature (nymph) stage, it is bright red with small dark wing pads being added as it grows.
In early spring (late April to early May), the adult female emerges from her overwintering site to lay eggs on the young leaves and seed pods and in bark crevices of the boxelder plant. The freshly laid eggs turn from yellow to red as the embryo develops. Once the nymphs appear in late spring to early summer, they develop rapidly, feeding on the seeds and immature leaves of the boxelder. A true bug with sucking mouthparts, the boxelder bug’s feeding will damage and distort the tender young leaf growth.
In years with higher infestations, the boxelder nymph will also seek out seedbearing silver maples, ash, apple, and plum trees, where it can cause deformities and blemishes in the fruit. An adult female can produce one to two generations per year before seeking a place to hibernate for the winter. It is during this process of looking for overwintering sites that the boxelder bug is most commonly seen, and on a warm autumn day, you will find them congregating on the sunny sides of tree trunks and buildings.
The most effective way to manage boxelder bug infestations is to remove its primary host plant, the boxelder tree, especially ones growing near foundations and buildings. If that is not an option, then diligence in sealing cracks and crevices around windows, doors, and building foundations is the next best method to eliminate their access to your home.
Indoors: the safest way to destroy them is by vacuuming because crushing their bodies will result in a permanent red stain.
Outdoors: Contact the Plant Clinic (630-719-2424 or email@example.com) for current recommendations.