Boxelder Bugs in Ohio: Why They Cover the Sunny Side of Your House Every Fall

The first cold snap of the fall is usually when the phone rings about boxelder bugs. A homeowner walks out to a south or west wall in the afternoon sun and finds it covered in slim black bugs with orange-red stripes, hundreds of them, and a few already inside around the window frames. Ohio State University Extension calls the boxelder bug the "poster child" for insects that invade homes in the fall, and Knox County gets its share.

What a boxelder bug looks like

Boxelder bugs run about 1/2 to 3/4 inch long. They are narrow and flat-backed, dark gray to brownish-black, with three bright orange-red stripes running lengthwise on the section just behind the head. They are true bugs, not beetles, and the ones on your house most likely came from a boxelder or maple close by.

Where they come from

The name is accurate. Boxelder bugs feed on the seeds of boxelder trees, and specifically the female trees, since only those produce seed. They also feed on other maples and on ash, among a long list of other plants. If you have a boxelder or a seed-heavy maple within a short walk of the house, that is the source.

Why the sunny side, and why the first cold snap

Ohio State describes the pattern in detail. During cold snaps in early fall the bugs gather on the west side of tree trunks to soak up solar heat. When a warm spell follows, the adults scatter to look for a place to spend the winter, and a warm, light-colored wall with a bit of loose trim is exactly what they want. Only the adults survive the winter, so the crowd on your siding is the generation that will reappear in spring.

They are not trying to get into your living room. The bugs are following warmth into cracks and ending up in wall voids and attics. Some follow that warmth all the way into heated rooms by accident, which is why they turn up on windowsills on warm winter days.

Do boxelder bugs bite or cause damage?

Extension fact sheets treat them as a nuisance pest rather than a health threat, and they do not damage the structure. The two real problems are stains and smell. The fluid inside a boxelder bug can leave a permanent mark on furniture, carpet and walls, and a disturbed or crushed bug releases what Ohio State describes as a cloying, foul-smelling defensive chemical. Do not swat them on a light-colored wall.

Keeping them out: an ounce of caulking

Ohio State's advice is blunt: "an ounce of caulking is worth a pound of bugs." The entry points are the ones you would guess and a few you would not.

• Old caulking that has pulled away from window frames and door jambs.
• Loose siding and rips in window screens.
• Worn exterior door sweeps, including the door into an attached garage.
• Unscreened attic vents, and bathroom or kitchen exhaust vents with no protection.
• Gaps where soffits fit loosely against the wall.

Sealing is worth doing before the first cold snap, not after the bugs are already in the walls. For a house that gets hit every year, an exterior treatment of the warm-side walls in late September does the rest. That is the same service we run for stink bugs and Asian lady beetles, since all three arrive the same way at the same time; see our stink bug and fall invader control page for how the inspection and treatment work.

Once they are inside

There is no effective trap for boxelder bugs, so it is collection. A plastic water bottle makes a simple bug collector, with a little soapy water in the bottom if you are dealing with numbers. A vacuum works, but avoid running an unmodified direct-fan vacuum over them, which crushes the bugs inside the machine and fills it with the smell. Slipping a nylon ankle sock into the hose so the bugs collect in the sock solves that.

The rest of the fall crowd

Boxelder bugs rarely show up alone. The same walls draw brown marmorated stink bugs, multicolored Asian lady beetles and cluster flies, plus the occasional western conifer seed bug, a larger bug you can pick out by the leaf-shaped flare on its hind legs. If you are not sure which one you have, our guide to Ohio's fall invaders puts them side by side, and the Asian lady beetle post covers the one that bites.

Frequently asked questions

Should I cut down the boxelder tree?

Only if you were going to anyway. Removing one tree rarely solves it, because the bugs also feed on maples and other common trees, and the ones on your house may have come from a neighbor's yard. Sealing the house and treating the exterior at the right time is more reliable.

Will they lay eggs in my house?

No. They overwinter as adults and go back outside in spring to feed and breed on trees. Nothing reproduces in your walls.

Why do I still see them in January?

Warm winter days wake them up. Bugs tucked into wall voids follow the heat toward the rooms and show up on sunny windowsills, then go dormant again when it cools.