The box elder bug, known scientifically as Boisea trivittata, is a common North American insect that often causes concern when it congregates on homes. These insects are classified as true bugs and are recognizable by their distinct coloration and tendency to gather in large masses. The adult box elder bug possesses fully developed wings and is capable of flight. This ability allows them to move between feeding areas and suitable overwintering sites across significant distances.
How and When Box Elder Bugs Fly
The capacity for flight is limited to the adult stage, as the immature nymphs are wingless. Adults emerge from overwintering locations in spring and fly toward host trees to feed and reproduce. Throughout the warmer months, they use their wings primarily for short-distance travel between feeding and mating sites on the trees.
The most noticeable flights occur later in the year during late summer and early autumn. This is when the second generation of adults prepares for the winter, triggering a mass migration behavior. They take to the air to search for warm, sheltered places to hibernate. While not agile fliers, these insects are capable of traveling up to two miles to find a suitable structure, often a home, where they can survive cold temperatures.
They are attracted to the warmth radiating from sun-exposed surfaces, particularly the south and west sides of buildings. This attraction causes large numbers of bugs to aggregate on walls, often near windows and doors, before they attempt to crawl inside through any available crack or gap. Once inside wall voids or attics, they remain inactive until the warmth of spring or internal heating draws them out.
Identifying Features and Primary Habitat
The adult box elder bug is easily identified by its size and striking coloration, typically measuring about one-half inch in length. Their bodies are predominantly dark gray or black, contrasted by bright reddish-orange markings. These markings include three distinct red lines on the thorax and similar red lines along the edges of the wings.
When resting, the adult’s wings overlap flatly over the back, which often creates an observable “X” pattern. Nymphs lack full wings and are instead a bright, vivid red color. The common name derives from their association with the box elder tree (Acer negundo), which is their primary host plant.
They feed by piercing seeds, leaves, and tender twigs with their mouthparts, preferring the seed-bearing female box elder trees. They will also feed on other species of the maple family, such as silver and trident maples, and sometimes ash trees. The presence of these specific host trees in a landscape directly influences where population outbreaks are likely to occur.
Strategies for Exclusion and Prevention
Preventing box elder bugs from entering a structure focuses heavily on exclusion, particularly before the late-summer migration begins. Inspecting the exterior of the home and sealing all potential entry points is the most effective barrier. Use high-quality exterior caulk to close gaps around window frames, door casings, and where utility lines penetrate the siding.
Repairing or replacing damaged window and door screens is important, as is ensuring that chimney caps and soffit vents are securely screened. Weather-stripping on exterior doors should be in good condition, and door sweeps should be installed to eliminate gaps. Focus on walls that receive the most sun, typically the south and west sides, as these are the areas where the bugs most often congregate.
For populations clustering on the exterior of the home, non-chemical control methods are practical and effective. A strong stream of water from a garden hose can be used to wash clusters of bugs off walls and tree trunks. If bugs have already entered the living space, physical removal with a vacuum cleaner is the recommended course of action. Immediately disposing of the vacuum bag after use prevents the captured bugs from escaping.