Boxelder Bugs and Stink Bugs in Oregon

Written by Jacob Lander, owner and ODA-licensed applicator · Updated October 2026

What are the red and black bugs all over my house? In Oregon, they’re almost always western boxelder bugs. They’re about half an inch long, black with red lines, and they gather on sunny walls in fall looking for a place to spend the winter. They won’t hurt you, damage your house or breed indoors. Brown, shield-shaped bugs showing up at the same time are stink bugs.

Every fall we get the same call: one side of the house is covered in bugs. It’s usually boxelder bugs, sometimes stink bugs, often both. They’re harmless, but that doesn’t help much when they’re coating the siding and turning up on every windowsill.

This guide covers how to tell the two apart, why they pick your house over the neighbor’s, and what actually keeps them out. Short version: timing matters more than spray.

Why are boxelder bugs all over my house?

Boxelder bugs live on boxelder trees and other maples. In fall, the adults leave the trees in large numbers and look for a protected place to spend the winter. A warm, sunny wall is the first stop. From there they crawl into gaps around windows, doors, siding and vents.

Why your house and not the one next door? OSU Extension says they go for tall buildings and rough surfaces, so two-story homes get more of them, and they favor houses with big trees right next to the structure. A maple or boxelder in the yard plus a tall wall that catches the sun is the classic setup.

Are boxelder bugs harmful?

No. OSU Extension says boxelder bugs cause no damage to homes and won’t harm people. They also don’t breed indoors, so the bugs inside your house are the ones that got in during fall, not a growing infestation.

The real problems are smaller:

• Their droppings can spot curtains, walls and furniture.
• Crushing them leaves a stain.
• The ones that make it into walls and attics can stay all winter.

Boxelder bugs covering the siding right now? We treat homes all over Oregon. Get a free quote.

What’s the difference between boxelder bugs and stink bugs?

Both show up on Oregon homes in fall, and both are trying to get inside for the winter. Up close, they look nothing alike:

• Boxelder bugs are narrow, black with red lines and about half an inch long. They’re native to the West, and they cluster in big groups on sunny walls.
• Brown marmorated stink bugs are mottled brownish-gray and shaped like a shield. They’re from Asia, were first found in Oregon in 2004, and are most common in the Willamette Valley. They give off a strong smell when disturbed, and they feed on crops and garden plants.

Neither one damages your house or is a health risk. Stink bugs are the worse houseguest because of the smell.

You’ll also hear boxelder bugs called boxelder beetles. They aren’t beetles. Both are true bugs, with mouthparts built for sucking plant juices.

When do boxelder bugs show up in Oregon?

• September and October: adults leave the trees, gather on sunny walls, then work their way into gaps. This is when most people notice them.
• Winter: the ones that got in stay hidden in walls, attics and window frames. Some wander out into rooms.
• Spring: survivors fly back to the maples and boxelders to lay eggs.
• Summer: the young feed and grow on the trees. You’ll barely see them.

There’s one generation a year, and next fall’s bugs will go looking for the same warm wall.

How do I keep boxelder bugs out of my house?

Seal first, and treat early. Both bugs get in through gaps, and once they’re inside, spraying doesn’t do much. OSU Extension notes that insecticides aren’t very effective after the weather turns cold. The Oregon Department of Agriculture makes the same point about stink bugs: spray inside, and more will come in to replace them unless the gaps are sealed.

• Seal gaps before fall. Caulk cracks around windows and doors, siding joints, and where pipes and wires come through.
• Repair window and door screens. Torn screens let them walk right in.
• Treat the outside early. A residual treatment on exterior walls works in early fall, before the bugs gather. Once it turns cold, it’s too late for the season.
• Vacuum the ones inside. Don’t crush them. Empty the vacuum outside so they don’t crawl back out.

How Bug Zapper handles boxelder bugs and stink bugs

We start by brushing down the whole house. That clears the webs and knocks the clusters off the siding, which shows us where the bugs are getting in. Then we treat the full perimeter, plus doors, windows and under the eaves.

Boxelder bugs fly, so they can skip right over a barrier at ground level. That’s why we treat high and low, as much of the structure as we can reach.

On a plan, if they come back, so do we, at no extra cost. That’s our 1-year Pest-Free Promise. See plans and pricing, or read more about both bugs in our pest library.

Boxelder bugs on the siding? Stink bugs in the windows? We should talk. Call 541-636-0146 or get a free quote.

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Sources

• Oregon State University Entomology: Box Elder Bug (PDF)
• Pacific Northwest Insect Management Handbook: Western boxelder bug
• KTVZ, Oct. 2, 2015, quoting ODA entomologist Jim LaBonte: Brown marmorated stink bug invading Oregon homes