The box elder bug (Boisea trivittata) is a common insect found throughout North America. They are generally considered nuisance pests rather than a significant threat to health or property. The primary concern stems from their tendency to congregate in large numbers, especially in the fall as they seek overwintering sites. These bugs are not medically dangerous to either humans or household pets.
Identifying the Box Elder Bug
The adult box elder bug is easily recognized by its distinctive coloration, typically growing to about a half-inch in length. Their bodies are predominantly dark brown or black, featuring prominent reddish-orange markings. Specifically, they have three longitudinal red stripes on the thorax and red margins along the basal half of their wings. When their wings are spread, a bright red abdomen is visible beneath the dark forewings.
These insects undergo three life stages: egg, nymph, and adult. The nymphs, which hatch from red eggs laid in the spring, are wingless and appear bright red with a darker head. They gradually develop the adult’s black and red patterns as they molt. Aggregations of adult bugs become most noticeable in the late summer and fall as they seek warm, sheltered places to hibernate.
Physical Threat to Humans and Pets
Box elder bugs pose virtually no physical or medical danger to people or animals. They do not possess a stinger and are not known to bite, as their mouthparts are designed for piercing and sucking plant fluids, not for feeding on mammals. Furthermore, these insects are not carriers or transmitters of any diseases to humans or pets. They are considered harmless from a health perspective.
The only minor health-related issue is the potential for allergic reactions in rare, susceptible individuals exposed to high concentrations. More commonly, their primary offense is staining: when crushed, they release a foul-smelling fluid that can leave a reddish-brown stain on surfaces. This fluid can be an irritant, but it does not cause serious harm.
Impact on Structures and Plants
Box elder bugs do not cause structural damage since they do not bore into wood or consume building materials. They are attracted to structures only as overwintering shelters, typically entering through small cracks, gaps, or poorly sealed windows and foundations. Once inside, they remain inactive and do not reproduce, although they may emerge into living spaces on warmer winter days.
Regarding plants, they primarily feed on the seeds and leaves of box elder trees, as well as occasionally maples and ashes, using piercing-sucking mouthparts to extract sap. While heavy feeding can lead to minor distortion or yellowing of leaves, they rarely cause significant, long-term damage to mature trees. They are sometimes found feeding on the fruit of strawberry or raspberry plants, but they are not considered a major agricultural pest.
Managing Nuisance Infestations
The most effective method for managing box elder bugs is preventing their entry into the home before they seek shelter in the fall. Homeowners should seal all potential entry points, such as cracks around utility pipes, doors, and windows, using caulk, weatherstripping, or fine-mesh screening before September. Repairing damaged window and door screens is also a simple, proactive exclusion step.
Once the bugs have entered the home, physical removal is the safest and most practical method. Vacuuming up the insects and immediately disposing of the sealed bag outdoors prevents staining or odors from crushing them. For large exterior aggregations, a forceful stream of water or a soapy water spray can be used. Chemical control is generally unnecessary, but professional application of a residual spray may be considered for severe outdoor infestations.