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

1. Vacuum the ones that get in. Don't crush boxelder bugs, since they can stain.
2. For cluster flies in the attic, vacuum them rather than spraying.
3. 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.