Boxelder Bugs and Cluster Flies: Fall Invaders Explained
Two very different insects show up in the same season for the same reason: they want a warm place to wait out winter. Neither one breeds in your home.
Boxelder bugs
- About half an inch long, black with red-orange lines on the back.
- Gather on sunny walls, especially near boxelder, maple, and ash trees.
- Harmless to people. Their droppings can stain fabric.
Cluster flies
- A bit larger than a house fly, dark gray with fine golden hairs, and the wings overlap at rest.
- Slow and sluggish, often buzzing at windows on warm winter days.
- They aren't from garbage or filth. They develop outdoors, and the adults slip into walls and attics for winter.
What to do
- Vacuum the ones that get in. Don't crush boxelder bugs, since they can stain.
- For cluster flies in the attic, vacuum them rather than spraying.
- Avoid bug bombs and store-bought sprays indoors. They don't reach the insects hiding in the walls.
When to call a pro
If you get large numbers every year, contact a professional in early fall, before they come in. They can close the entry points and treat the outside of your home.