The boxelder bug (Boisea trivittata) is a common insect recognizable by its black body and distinct reddish-orange markings, including three stripes running lengthwise behind its head. While they do not pose a threat to human health or the structure of a home, these insects frequently become a nuisance when they gather in large numbers. Understanding where these bugs spend their lives is the first step in managing their populations, as their habitats change dramatically between the warm summer months and the cold winter season.
Primary Feeding Locations
Boxelder bugs are associated almost exclusively with certain host trees, primarily the boxelder tree, from which they derive their common name. They possess piercing-sucking mouthparts, which they use to extract fluids from the plant material.
Nymphs and adults feed predominantly on the seeds and developing leaves of these trees. Female boxelder trees are especially attractive because they produce the seed-bearing racemes, which are the main food source for developing nymphs. The bugs will also utilize other species of the maple family, such as silver maple, as well as ash trees, though they cannot complete their entire life cycle on these secondary hosts.
Overwintering Congregation Sites
As the weather cools in late summer, the focus of the adult boxelder bugs shifts from feeding to locating a safe, dry place to enter dormancy. These insects are cold-intolerant and require protected environments to survive the winter. This search leads them to congregate on various outdoor structures.
Common outdoor sites include sheltered areas:
- Under rocks
- Beneath loose tree bark
- In wood piles
- Within accumulated leaf litter near foundations
The most problematic congregation sites are the cracks and crevices of human structures. They seek entry points such as gaps around window and door frames, utility penetrations for pipes and wires, and unsealed foundation cracks.
These insects will exploit any opening larger than about 1/8th of an inch, using structural voids behind siding, within attics, or in wall spaces as their preferred overwintering habitat. They cluster together in these voids to insulate themselves and minimize heat loss. Boxelder bugs remain inactive in these concealed spaces throughout the cold months, only occasionally emerging if the temperature rises sufficiently during a warm spell.
Why They Migrate Indoors
Their annual movement is linked to the dropping temperatures of early autumn, typically spanning from late August through November. The adult bugs must accumulate enough solar heat to prepare for their overwintering phase, driving them to migrate from host trees toward buildings that retain warmth.
Boxelder bugs are attracted to warm surfaces and will cluster on the exterior walls of a home, especially those facing south and west, which receive the most prolonged sun exposure. They bask in the sun to warm their bodies before attempting to find a structural breach. Once an entry point is located, they push their way into the interior voids of the structure, seeking a stable, dry environment to enter diapause. They are not seeking food or a place to reproduce when they enter a home, but solely a sheltered space to survive until spring.
Home Management and Exclusion
Preventing their entry into the structure before the overwintering migration begins is the most effective management strategy. Homeowners should inspect the building envelope, sealing all gaps and cracks around windows, doors, roof lines, and utility conduits. Installing door sweeps and ensuring that all window and roof vent screens are intact will eliminate many potential access points.
Once the insects have entered wall voids, chemical treatments are impractical. For bugs that emerge into the living space, the cleanest method for removal is using a vacuum cleaner. Crushing the insects should be avoided, as they release a pungent odor and their internal contents can stain curtains, carpets, and walls. These bugs are not known to cause structural damage and are harmless to people and pets, though they are a nuisance when present in large numbers.