The boxelder bug (Boisea trivittata) is a common, small, black, and red-marked insect. They spend warmer months feeding on the seeds of boxelder, maple, and ash trees. As temperatures drop in late summer and early fall, adult boxelder bugs begin a seasonal migration to find warm, protected places to survive the winter. They enter a state of reduced activity within sheltered spaces, often inside homes and buildings.
The Overwintering State
Boxelder bugs do not truly hibernate like mammals. Instead, they enter diapause, a state of suspended development. This involuntary physiological state is triggered by environmental cues such as decreasing daylight and falling temperatures. During diapause, the insect’s metabolism significantly slows down, allowing it to survive for extended periods without feeding.
The adult bugs rely entirely on stored fat reserves accumulated during the summer and fall. They are not feeding, mating, or reproducing while in this semi-dormant condition. This strategy allows only fully grown adults to successfully pass the winter and emerge in the spring. Since they do not feed on the structure or reproduce indoors, the primary concern is their presence as a clustering pest.
Seeking Shelter and Entry Points
The bugs are strongly attracted to warm, sun-exposed surfaces in the fall, often aggregating in large numbers on the southern and western sides of buildings. These walls provide the necessary warmth for the insects to prepare for winter dormancy. Once aggregated, they search for the smallest openings to move from the exterior into protected void spaces. Due to their flat bodies, they are capable of squeezing through incredibly small gaps.
Common entry points include cracks around window and door frames, gaps in utility line penetrations, and poorly sealed roof and soffit vents. They also use spaces between siding and the foundation, or cracks in fascia boards, to access wall voids, attics, and crawl spaces. They seek the warmest, driest, and most secluded voids within the home for the winter.
Seasonal Timing and Spring Emergence
The migration toward overwintering sites typically begins when outdoor temperatures consistently drop below 60°F, usually from early September through October. This movement is driven by the instinct to find a safe location before freezing weather begins. Once settled into a protected void, they remain mostly inactive throughout the coldest months.
If boxelder bugs are seen crawling inside during mid-winter, they have usually been reactivated by temporary spikes in the home’s interior temperature. The warmth from the heating system can penetrate wall voids and trick the bugs into thinking spring has arrived, causing them to emerge into the living space. The true mass emergence happens in early spring when outdoor temperatures rise consistently, prompting adults to leave the structure to find host trees, feed, and mate outdoors.
Exclusion and Indoor Management
The most effective long-term strategy for managing boxelder bugs is exclusion, which means physically preventing their entry into the structure. In late summer and early fall, inspect the entire exterior of the home, focusing on sunny, exposed walls. This exclusion work is labor-intensive but provides lasting protection against overwintering pests.
Exclusion Methods
Seal all visible cracks and crevices using a high-quality silicone or silicon-latex caulk. Repair any damaged window and door screens, and ensure all vents, including those in the roof and attic, are covered with fine-mesh screening. Install door sweeps on all exterior doors to eliminate gaps at the threshold.
Indoor Management
For bugs found indoors, physical removal is the preferred method. Use a vacuum cleaner to safely collect the insects, and immediately dispose of the vacuum bag or contents outdoors. Crushing boxelder bugs should be avoided because they release a foul odor and can leave a reddish-orange stain on fabrics, walls, and upholstery. Insecticide sprays are ineffective against bugs hiding within wall voids and are not recommended for managing pests once they are inside the home.