Boxelder Bug Identification Guide
Boxelder bugs (Boisea trivittata) are among Philadelphia's most recognized fall invaders. Flat, 0.5-inch insects with distinctive black bodies and bright red/orange wing markings, they mass on warm south-facing walls in September–October seeking overwintering sites. They do not reproduce indoors, do not bite, and do not damage structures — but their sheer numbers and foul smell when crushed make them a significant nuisance.
Low concern
| Quick ID Reference |
|---|
| Size | 0.5 inch |
| Color | Black with red/orange wing markings |
| Host Tree | Female boxelder tree (Acer negundo) |
| Season | Spring–summer on trees; fall invasion of structures |
| Indoors | Overwinter in wall voids, do not reproduce |
| Danger | None — stains only |
Frequently Asked Questions
Why are boxelder bugs on my house?
Your home's south or west-facing walls are warm. Boxelder bugs gather there in fall to thermoregulate before entering wall voids to overwinter. They're attracted to heat reflecting from siding, bricks, and windows.
Are boxelder bugs harmful?
Boxelder bugs do not bite, sting, or spread disease. They do not damage structures. If crushed, they leave a reddish-orange stain on fabrics and surfaces. Their fecal matter can also stain.
How do I keep boxelder bugs out?
Seal gaps around windows, doors, utility penetrations, and siding. Use a perimeter insecticide spray in September before they enter. Remove or avoid planting female boxelder or silver maple trees near your home.
When should I call a pest control professional?
If you're seeing large numbers, finding entry points you can't seal, or if the infestation is affecting your quality of life, City Best Pest Control offers free inspections for Philadelphia, Montgomery County, Delaware County, and Bucks County residents. Contact us here.
