The box elder bug (Boisea trivittatus) is a common North American insect recognizable by its black body marked with distinct red-orange lines along the edges and three stripes behind the head. These insects are often found congregating on the sunny sides of buildings, especially in the fall. They emit a strong, unpleasant scent when they are crushed or otherwise threatened.
The Source of the Odor
The odor released by the box elder bug is a defensive mechanism designed to deter potential predators. When the insect is physically harmed or severely threatened, it secretes a pungent compound from specialized glands in its body. This foul-smelling substance serves as a chemical warning, signaling to birds or other animals that the insect is unpalatable.
While the smell is generally harmless to humans, it is intensely disagreeable. The scent is often described as acrid, pungent, or resembling decaying matter or rotten fruit with a hint of acetone. This compound can also leave a brownish-red stain on curtains, walls, or carpets if the bug is squashed indoors. Therefore, it is recommended to avoid killing these insects by squashing them.
Common Habitats and Entry Points
Box elder bugs spend the warmer months feeding primarily on the seeds of female box elder, maple, and ash trees. They use piercing-sucking mouthparts to extract fluids from seeds, leaves, and sometimes fruit. Their presence becomes most noticeable in late summer and early fall as temperatures begin to drop.
In late summer and early fall, large groups of adult bugs seek sheltered locations for overwintering. They are strongly attracted to the warmth radiated by structures, especially those with southern or western exposures. This search for shelter drives them toward homes and buildings.
They gain entry through small structural vulnerabilities, taking advantage of cracks and crevices around the foundation. Common entry points include gaps where utility lines or plumbing enter the home, loose-fitting window screens, and poorly sealed door and window frames. Once inside, they remain dormant until warmer weather in the spring causes them to become active, often emerging into living spaces.
Non-Chemical Management Strategies
The most effective way to manage box elder bugs already inside the home is through physical removal, specifically by using a vacuum cleaner with a hose attachment. Vacuuming allows for the collection and disposal of the insects without crushing them, preventing the release of the staining and odorous defensive compound. After collection, the vacuum bag should be immediately sealed and discarded outdoors to prevent the bugs from escaping.
For managing large clusters of bugs on the exterior of a home or on trees, a simple solution of water and a few drops of liquid dish soap is effective. The soapy water works by disrupting the insect’s outer layer, leading to dehydration. This solution is best applied directly to the congregations of bugs using a spray bottle or garden sprayer.
The best long-term strategy for control involves exclusion, which means sealing the bugs out before they can enter to overwinter. This requires a thorough inspection and repair of the building envelope, especially in late summer before their migration begins. Sealing exterior cracks and holes with caulk is important, and all window screens must be fully intact and tightly fitted. Applying weatherstripping to exterior doors and windows will also close off common access points.