The Boxelder Bug (Boisea trivittata) is a common North American insect. It is distinguished by its black body marked with bright reddish-orange lines on its back and wing edges, growing to about a half-inch in length. These insects are frequently seen clustering in large numbers, often causing concern for homeowners. Despite their appearance, the boxelder bug is considered a nuisance pest, not a destructive one, and does not cause fatal damage to mature, healthy trees.
The Type of Damage Boxelder Bugs Cause
The boxelder bug feeds using piercing-sucking mouthparts, which it inserts into plant tissue to extract sap and fluids. This feeding method limits their potential for serious harm, as they are not wood-boring insects or bark strippers. The damage caused by their feeding is cosmetic and short-term, especially on established trees.
When populations are high, feeding can result in subtle visible symptoms on the foliage. Gardeners may notice minor leaf distortion, discoloration, or small yellow or brown speckles on leaves where the bugs have fed. This effect, often called stippling or spotting, does not affect the tree’s overall health or long-term vigor.
Damage can also occur on developing seeds and soft stone fruits, such as apples, plums, and cherries. Feeding on fruit can cause small pits or dimples on the surface, creating defects in commercial orchards, but this is rarely a significant issue for backyard trees. The bugs may also leave behind tiny dark droppings, or frass, on leaves and fruit, which is an aesthetic issue during heavy infestations.
Preferred Host Trees and Feeding Habits
Boxelder bugs owe their name to their primary food source, the Boxelder tree (Acer negundo), a species of maple. Their diet consists mainly of the seeds, seedpods, and sap from these trees. They are particularly attracted to female boxelder trees because these produce the seed-bearing samaras they prefer to feed upon.
The bugs also feed on other trees in the maple family, such as silver maple (Acer saccharinum) and ash trees, especially when their preferred food source is scarce. Nymphs, or young bugs, are bright red and emerge in the spring. They feed initially on fallen seeds before moving up the tree to newly developing leaves and seeds. Adults and nymphs insert their proboscis to extract sugary fluids, focusing on tender growth rather than woody tissue.
Adult females lay their eggs on the host tree’s bark crevices or leaves in the spring, with one to two generations developing per year. As temperatures cool in late summer and fall, the adult bugs congregate on sunny surfaces to seek warm, protected sites for overwintering. This behavior is the main reason they become a nuisance, as they often migrate great distances from their host trees to find shelter in homes and buildings.
Managing Infestations
Managing boxelder bugs involves addressing two issues: their presence on trees and their tendency to invade structures as a nuisance pest. Since damage to healthy trees is negligible, chemical treatments on the trees are often unnecessary unless the population is massive and the tree is stressed. A strong jet of water can be used to dislodge clusters of bugs from tree trunks or walls, which is a simple, non-chemical control method.
For the nuisance problem of bugs aggregating around the home, the most effective strategy is exclusion. Sealing exterior cracks and gaps around doors, windows, and utility lines prevents them from entering wall voids and living spaces. This sealing should be done by late August or early September, before the bugs begin their fall migration in search of overwintering sites.
If bugs have already gathered on the exterior of a home, a perimeter application of residual insecticide can be applied by a professional to the foundation and around entry points. Inside the home, the only practical control method is physical removal, usually using a vacuum cleaner, as chemical treatment of wall voids is not recommended. Removing female boxelder trees near a home can reduce the source of the infestation, but since the bugs travel long distances, this is not a guarantee of complete control.