The Boxelder bug, scientifically known as Boisea trivittata, is a common insect found across North America. This species belongs to the “true bug” order and is recognized as a nuisance pest rather than a dangerous one. Understanding their behavior, life cycle, and characteristics is key to understanding why they often appear in large groups near human dwellings. This analysis explains their actions, the concerns they raise for homeowners, and practical methods for managing their presence.
Identifying Characteristics and Diet
Adult Boxelder bugs are distinctively marked, typically growing to about half an inch (13 millimeters) in length. Their bodies are dark brown or black, featuring three longitudinal red or orange stripes on the thorax and prominent red margins on the edges of their wings. Juvenile Boxelder bugs, known as nymphs, are wingless and bright red, often clustering together on their host plants. These insects feed primarily on the seeds of the female Boxelder trees (Acer negundo). They use specialized piercing-sucking mouthparts to extract sap from the seeds, leaves, and tender twigs. While the Boxelder tree is their main food source, they will also feed on other trees in the maple and ash families. This feeding activity rarely causes significant damage to healthy, mature trees.
Seasonal Migration and Swarming
The behavior that most concerns homeowners is the Boxelder bug’s annual movement, which occurs in late summer and early fall. As temperatures begin to drop, the adults start a collective migration to find suitable overwintering sites, a process known as diapause. They are strongly attracted to warmth, causing them to aggregate in massive clusters on sunny surfaces, particularly the south and west-facing walls of buildings. This swarming behavior is a prelude to their search for shelter, and they can fly up to two miles to find a protected location. They seek out cracks and small openings in structures, where they will remain inactive throughout the cold months. Once spring arrives, the surviving adults emerge to fly back to their host trees to feed and reproduce, beginning the cycle anew.
Property Damage and Health Concerns
Boxelder bugs are not known to cause structural damage to buildings or homes, but their presence can still be problematic. When large groups gather and enter a structure, they can leave behind reddish-orange or brown fecal droppings that stain light-colored surfaces, including curtains, upholstery, and walls. A more immediate issue arises when the bugs are crushed. If a bug is smashed, it releases a pungent odor as a defensive mechanism. This action can also leave a noticeable reddish stain on the surface where it occurred. Boxelder bugs are not known to sting or transmit diseases to humans or pets. Although they possess piercing mouthparts, biting is rare and typically only happens defensively if they are handled or feel threatened, resulting in a minor, temporary skin irritation.
Stopping Their Entry
The most effective strategy for managing Boxelder bugs is physical exclusion, focusing on preventing them from entering a structure in the fall. Homeowners should conduct a thorough inspection of the building exterior, paying close attention to potential entry points. All cracks and gaps in the foundation, siding, and utility line entry points should be sealed with a high-quality caulk. Repairing or replacing damaged window and door screens is necessary to block access. Installing weather stripping around all exterior doors and windows, along with door sweeps, helps to eliminate small gaps at ground level. These measures prevent the bugs from completing their overwintering migration into sheltered spaces, keeping the nuisance population outside where they can overwinter under debris or bark instead.