As their name suggests boxelder bugs can most often be found living, breeding, and feeding on boxelder trees. Along with boxelder trees they can be found on ash, maple, apple, plum, and other seed-bearing trees. Boxelder bugs feed on the soft plant tissues of the tree-like leaves, flowers, and young green twigs. Using their specialized mouthparts, they suck liquid from the tree. Generally, the damage they inflict on a tree is quite minimal except in cases of very large infestations.
When the weather begins to cool in the fall adult boxelder bugs will flock to the sunny side of homes. This is when they may inadvertently come inside through cracks and crevices in exterior walls, gaps around windows and doors, and through vents. When they move into homes they like to go behind walls, under floors, and into crawl spaces to spend the winter in. In the spring they find their way back outside to feed and breed.
If the weather warms during the winter they may emerge and become a nuisance throughout your home. Often they fly to windows and stain upholstery and other fabric items in your home with their feces.