The box elder bug (Boisea trivittata) is a common North American insect that frequently becomes a household nuisance, particularly as the weather cools in the autumn. These black and red insects are often seen aggregating in large numbers on the sunny sides of homes, leading many people to be concerned about potential risks. Understanding the biology and habits of this true bug helps address worries about its presence.
Do Box Elder Bugs Pose a Threat?
Box elder bugs do not pose a health threat to humans or household pets and are considered a nuisance pest rather than a harmful one. They are not known to bite defensively or offensively, nor do they transmit diseases. These insects possess piercing-sucking mouthparts designed for feeding on plant materials, specifically the seeds and leaves of box elder, maple, and ash trees.
Their mouthparts, used to extract sap from plants, are theoretically capable of puncturing human skin. However, a “bite” is extremely rare and typically only occurs if the insect is handled roughly or trapped against the skin. Any resulting irritation is minor, resembling a tiny, temporary red mark, and is not a true defensive bite. Pets may experience vomiting if they ingest a bug due to its unpleasant taste, but the insect is not venomous.
Identifying Box Elder Bugs and Their Habits
Adult box elder bugs are characterized by their dark, charcoal-black bodies, measuring about one-half inch in length. They have distinctive reddish-orange markings, including three lengthwise stripes on the thorax just behind the head, and red edges outlining the wings. When the wings are laid flat, they may form an ‘X’ or ‘V’ pattern.
The young, or nymphs, look different from the adults, emerging from eggs as bright red insects with black legs and antennae. They gradually darken as they mature through five growth stages, developing black wing pads. These insects are most noticeable in the late summer and fall because they aggregate in large masses on sun-exposed surfaces like rocks, trees, and building exterior walls. This behavior is driven by their need to find warm, sheltered locations, such as wall voids or attics, to survive the cold winter months.
Preventing and Managing Indoor Aggregation
The most effective strategy for managing box elder bugs is exclusion, preventing them from entering your home. Before the cooling temperatures of late summer and early fall prompt their search for shelter, homeowners should seal all potential entry points. This involves using caulk to fill cracks around window frames, utility pipes, and door casings, and ensuring weather stripping is intact.
Repairing or replacing damaged window and door screens is important, as these insects can squeeze through small openings. If the bugs have already made their way inside, the best removal method is using a vacuum cleaner with a hose attachment. This prevents the release of the foul odor the bugs emit when crushed, which can stain fabrics and walls. The vacuum contents should be immediately emptied outdoors into a sealed bag or bucket of soapy water to prevent re-entry. For large outdoor aggregations, a simple mixture of water and a few drops of liquid dish soap sprayed directly onto the clusters is an effective, non-chemical control method.