Boxelder Bugs
Boisea trivittata
NuisanceWhat it is
Black-and-red true bugs associated with boxelder and some maple trees. They often gather on sunny exterior walls and enter buildings in large numbers to overwinter.
How to recognize it
- About 1/2 inch long, flat and narrow
- Black with red-orange lines on the back and along the wing edges
- Gather in clusters on sunny walls, fences, and tree trunks
- Found near boxelder, maple, and ash trees
Where you will find it
Sunny sides of buildings and near their host trees in summer, then cracks, attics, and wall voids in fall and winter.
Found across much of the US.
Why it matters
They enter in large numbers in fall to overwinter. They do not damage a house, but they stain and are a nuisance.
Look-alikes
- Red-shouldered bug: Similar colors, but has red shoulders and is usually found near soapberry trees rather than gathering on houses.
- Large milkweed bug: Bright orange and black, found on milkweed, and not a home invader.
What to do
- Vacuum them up and empty the vacuum. Don't crush them, since they can stain.
- Skip indoor sprays and bug bombs.
- Contact a professional in early fall, before they move in.
When to call a professional
- You get large numbers every year.
- You want exterior treatment timed for early fall.
Questions
Do boxelder bugs bite?
They rarely bite, and their bites are not harmful.
Do they damage my home?
No. Their droppings can stain fabric and surfaces.
Why are they on one side of my house?
They gather on warm, sunny walls in fall.
Related reading
- Boxelder Bugs and Cluster Flies: Fall Invaders Explained
- Stink Bugs in the House: Why They Come In and What to Do
Related pests
Occasional Invaders
A broad category for pests that enter buildings incidentally but usually do not reproduce indoors. Examples can include boxelder bugs, lady beetles, millipedes, ground beetles, and other seasonal invaders.
Read more →Stink Bugs
Shield-shaped true bugs that release a strong odor when disturbed. Some species damage crops, while others enter buildings in fall to overwinter and become nuisance invaders.
Read more →Clover Mites
Tiny reddish mites that feed on grasses and ornamental plants. They often invade buildings in large numbers around windows and foundations but do not bite people or damage household items.
Read more →Cluster Flies
Slow-moving flies that enter buildings in late summer or fall to overwinter in attics and wall voids. Their larvae develop as parasites of earthworms outdoors; indoor adults do not breed in garbage or drains.
Read more →This page is general information, not a diagnosis. Pests vary by region and situation, and an on-site inspection is the reliable way to know what you have.