The boxelder bug (Boisea trivittata) is a common insect recognizable by its black body and distinct red markings. They frequently become a nuisance when they gather near homes. Boxelder bugs are highly selective in their diet, primarily feeding on the seeds and leaves of specific trees. They do not typically cause significant damage to common garden plants.
Primary Food Sources and Feeding Habits
The boxelder bug’s diet is strongly tied to the presence of trees within the Acer genus, including maples and, most notably, the boxelder tree (Acer negundo). They possess piercing-sucking mouthparts, which allow them to extract sap and moisture from plant tissues. This mechanism is used to draw nutrients primarily from the seeds of female boxelder trees, which are their preferred host.
Nymphs and adults concentrate their feeding on young leaves, tender twigs, and the developing seeds of these host trees. They also feed opportunistically on low-growing vegetation or fallen seeds on the ground. When their primary food source is limited, they may feed on fruits like apples, pears, and grapes.
Assessing Plant Damage
Boxelder bugs are rarely considered serious agricultural pests or a threat to ornamental plants. The damage they cause to their primary host trees is cosmetic and minor, such as yellow spotting on leaves or slight distortion of new growth. The overall health of the boxelder or maple tree is seldom compromised.
When large populations feed on tender fruits, they can cause localized damage like dimpling, scarring, or deformation. This feeding is not widespread enough to be commercially significant, and they do not pose a threat to most garden vegetables or flowers. Homeowners find them more of a nuisance when they leave reddish-orange fecal stains on light-colored surfaces after clustering.
Why Boxelder Bugs Gather
Large groups of boxelder bugs are often mistaken for a massive feeding frenzy. However, these aggregations are primarily behavioral, driven by the need for warmth and shelter. As temperatures drop in the autumn, adult boxelder bugs migrate away from their host trees to find suitable overwintering sites.
They are attracted to warm, sunny surfaces, frequently clustering on the south and west-facing walls of buildings. They seek entry through small cracks and crevices to hibernate. The bugs remain dormant through the winter, emerging in the spring to seek host trees and begin reproduction.