The boxelder bug (Boisea trivittata) is a common insect across North America frequently noticed by homeowners. These insects often appear in large groups, congregating on warm surfaces near homes and trees. The main concern is whether these numerous insects pose a threat to garden plants, landscape ornamentals, or mature trees. Understanding the biology and feeding habits of Boisea trivittata helps clarify the actual level of risk they present to surrounding vegetation.
Identifying Boxelder Bugs
Adult boxelder bugs are slender, dark insects that measure about half an inch in length. Their bodies are predominantly black, featuring distinctive reddish-orange markings. Three red lines run longitudinally along the thorax, and additional red margins are visible on the wings.
The young, called nymphs, start as small, bright red insects after hatching. As they grow through several molting stages, their color gradually darkens. They develop black markings, eventually resembling the adults, but remain wingless until their final molt. Both adults and nymphs are often seen clustered together, especially in sunny locations.
Assessing Plant Damage
Boxelder bugs are classified as nuisance pests because they cause little significant damage to plants. They feed using piercing-sucking mouthparts, which they insert into plant tissue to extract fluids. Their preferred diet consists almost entirely of the seeds and reproductive structures of the Boxelder tree (Acer negundo), the source of their common name.
They show a strong preference for female Boxelder trees, which produce their primary food source: seed pods. While they may also feed on other species in the maple family, such as silver maple, and occasionally ash trees, this feeding is superficial. The bugs target developing seeds and tender new growth, like leaves and twigs, to consume the sap.
The cosmetic damage on host plants is usually minor and does not threaten the plant’s overall health. Feeding activity can sometimes lead to shriveled or deformed seeds or cause small, localized yellow spots on leaves. Feeding on non-host plants like fruits is rare and generally only occurs during heavy infestations when their primary food source is limited. They rarely cause defoliation or death in mature trees.
Managing Boxelder Nuisance
The primary issue boxelder bugs create for homeowners is their tendency to congregate en masse, not plant damage. In the late summer and early fall, large populations gather on sunny, south-facing walls, sidewalks, and patios. They seek warm locations and sheltered crevices to use as overwintering sites.
Once inside a home, they do not reproduce or feed on structural wood, but their presence is a household annoyance. When crushed, these insects release a foul odor and leave reddish-orange stains on light-colored surfaces. This staining is often the main reason homeowners seek control.
The most effective management strategy is exclusion, which involves sealing all potential entry points before the fall migration begins. Homeowners should use caulk to seal cracks around windows, utility lines, and foundations. They must also ensure all door sweeps and window screens are intact.
Physical removal of congregating bugs is also effective, often achieved by simply vacuuming them up and disposing of the contents. For heavy outdoor populations, removing nearby female Boxelder trees can eliminate the primary food source, though this is a drastic measure. Insecticidal soap or targeted perimeter treatments can be applied to the exterior foundation and sunny walls as a final step. This chemical approach is best used only on congregation sites.