Boxelder bugs are a common seasonal nuisance, distinguished by their black bodies and reddish-orange markings. They are not harmful to people, pets, or structures. However, they become annoying when they congregate in large, swarming numbers, often on the sunny sides of homes. If crushed, they emit an unpleasant odor and leave reddish-orange fecal spots that stain surfaces. Understanding their behavior is the first step in managing them effectively.
Understanding Why Boxelder Bugs Migrate Indoors
Boxelder bugs feed primarily on the seeds, leaves, and twigs of female, seed-bearing boxelder trees, though they also feed on maple and ash trees. As summer progresses, the bugs mature into adults and shift their focus to finding a protected site to survive the cold.
In late summer and early fall, adults search for overwintering sites. They are strongly attracted to warm, sun-exposed surfaces, often clustering on the south or west-facing walls of homes. The absorbed warmth signals them to seek cracks or gaps to access voids within the wall structure, remaining dormant until spring.
Sealing Entry Points for Structural Exclusion
The most effective long-term defense is blocking entry before the fall migration begins. Boxelder bugs have flat bodies and only require an opening of about one-eighth of an inch to squeeze inside, necessitating a detailed exterior inspection. Focus first on all utility penetrations, including where pipes, electrical conduits, and air conditioning lines enter the home.
Seal these gaps using durable materials such as flexible, weather-resistant silicone caulk. Pay special attention to windows and door frames, particularly where the frame meets the siding or foundation. Replace any worn or loose weather stripping to eliminate thin gaps. For larger, irregular openings, use expandable foam or copper mesh to fill the void before sealing over the top with caulk.
Upper areas of the home are also common entry points often overlooked. Ensure that all attic, roof, and soffit vents are fully covered with fine-mesh screening to prevent insect access. Promptly repair even small tears in window and door screens, as these provide an easy path indoors. Complete this structural exclusion work by early September, before the bugs begin clustering, to prevent an indoor infestation.
Immediate, Non-Toxic Removal Methods
If boxelder bugs enter a structure, physical removal is the most practical approach for indoor control. Vacuuming is the preferred method for removing large numbers of bugs from walls, window sills, and floors without crushing them. Use a vacuum with a disposable bag or a shop vacuum containing soapy water, and dispose of the contents immediately. This prevents escape and contains the unpleasant odor released when they are agitated.
For bugs clustered outdoors on siding, sidewalks, or tree trunks, a simple non-toxic spray provides a quick knockdown effect. A mixture of liquid dish soap and water kills the insects on contact by dissolving their protective waxy layer. Mix one or two tablespoons of liquid dish soap into a spray bottle filled with water.
Outdoor clusters can also be dislodged and killed using a strong stream of water from a garden hose. Forcefully spraying the bugs off the exterior of the house is particularly effective on the vulnerable nymphs, which are susceptible to drowning. For any method used, wash away the dead insects and clean the area with soapy water. This removes the aggregation pheromones they leave behind that attract more bugs.
Addressing the Source and Chemical Control Options
Long-term management requires addressing the insect’s primary food source. Since boxelder bugs feed and lay eggs predominantly on female boxelder trees, removing these seed-bearing host trees is the most definitive step to reduce local populations. If tree removal is not feasible, actively raking or vacuuming up fallen seeds beneath the trees reduces the food supply for developing nymphs.
If populations remain high, chemical intervention can be used strategically as a perimeter defense. Residual insecticides containing active ingredients like pyrethroids are applied to the exterior foundation and lower siding of the home. This creates a chemical barrier that kills adults attempting to cross into the structure for overwintering. The timing is crucial, as application must occur in the fall before the bugs begin their mass migration toward the building.
For maximum effectiveness and safety, perimeter insecticide application is often best managed by a licensed pest control professional, especially when treating vertical surfaces and utility entry points. Care must be taken to ensure these products do not contaminate nearby plants or run off into storm drains. Using these targeted controls in conjunction with structural sealing provides the most comprehensive management strategy.