Quick answer: The boxelder bugs Oregon homeowners see massed on south- and west-facing walls in October are adults looking for a place to spend the winter. They slip behind siding and into attics and wall voids, then wander indoors on warm winter days. They do not bite, breed indoors or damage anything, but they stain when crushed. Seal gaps and treat the exterior before the first cold snap.
Key takeaways
- Western boxelder bugs feed on seed-bearing boxelder and other maple trees all summer, then move to sunny walls in late September and October to find winter shelter.
- Adults overwinter behind siding, in window frames, attics and wall voids, and reappear indoors on warm winter days.
- They do not bite, feed, breed or cause structural damage indoors, but crushing them stains fabric and paint.
- Sealing gaps and a well-timed exterior treatment before the bugs enter work far better than spraying inside the house.
Why do boxelder bugs cover my house every October?
Because on a cool October afternoon your house is the warmest, driest thing in the neighborhood, and boxelder bugs are hunting for a place to wait out the winter.
Boxelder bugs spend spring and summer on their host trees. As days shorten and nights cool, the adults leave the trees and search for shelter. According to the National Pesticide Information Center at Oregon State University, they can fly up to two miles to find a suitable overwintering site, and they are drawn to the sunny exterior sides of buildings.
A south- or west-facing wall soaks up afternoon heat and holds it into the evening. Light-colored siding reflects even more, which is why a cream-colored house collects bugs while the shaded, dark house next door has few. The bugs bask on that wall, then work their way into the closest gaps: under lap siding, behind trim boards, around window frames and into soffit and attic vents. A few days of that, and a house with 20 bugs on the wall has hundreds tucked inside its skin.
Are the boxelder bugs Oregon homes get the same as the eastern kind?
Almost. The Willamette Valley has the western boxelder bug (Boisea rubrolineata), a close cousin of the eastern species, and the two look and behave nearly the same.
Adults are about 1/2 inch long, flat and narrow, dark gray to black with thin bright red lines on the back. Nymphs are bright red and wingless. The Pacific Northwest Pest Management Handbook lists boxelder as the main host, with maple and ash as secondary hosts, and notes that in heavy years the bugs also feed on developing apples, pears, grapes and stone fruit.
They lay red eggs in bark crevices, and there is a single generation each year. That matters: the bugs on your wall in October are the year’s only crop, and nothing new hatches until spring. Female (seed-bearing) boxelder trees are the big producers.
Where do boxelder bugs go in winter?
Into the walls. Most of the bugs that gathered on your siding in October are inside the wall voids, attic and window frames by November, and they stay there, mostly still, until warm weather stirs them.
A stretch of sunny days in January or February, common in a mild Salem winter, warms the wall enough to wake them. Some crawl back outside to bask. Others follow the warmth inward and come out around window frames, recessed lights and baseboard heaters. That is why you find a dozen on the living room window in January. They have been there since fall.
Indoors they do not feed, do not lay eggs and do not reproduce. Bugs that reach heated living space usually dry out and die within days. Crushed bugs stain fabric and paint, and their droppings can spot light-colored curtains. The real exodus is spring, when the survivors head back to the trees to mate.
Boxelder bug, stink bug or conifer seed bug? How to tell
Three insects swarm Willamette Valley walls in October, and they are easy to separate once you know the shapes: boxelder bugs are narrow and red-lined, stink bugs are shield-shaped, and conifer seed bugs have leaf-shaped flares on the back legs.
| Feature | Western boxelder bug | Brown marmorated stink bug | Western conifer seed bug |
|---|---|---|---|
| Size | About 1/2 inch | About 5/8 inch (dime-sized) | About 3/4 inch |
| Shape and color | Narrow and flat; black with thin red lines; nymphs bright red | Wide shield; mottled brown | Long and brownish with a faint white zigzag across the back |
| Host plants | Boxelder, maple, ash | Fruit, nuts, vegetables and many trees | Douglas-fir, pine and other conifers |
| Signature detail | Three red lines right behind the head | White bands on dark antennae, smooth shoulders | Leaf-shaped flares on the hind legs; loud buzz in flight |
| Indoor nuisance | Stains when crushed; droppings spot fabric | Strong odor when crushed or vacuumed | Piney smell when handled; otherwise none |
If your bugs are shield-shaped, read our guide to stink bugs in the house in fall. The two pests often share the same wall, and our stink bug service treats them together.
How to get rid of boxelder bugs: what works and what backfires
Sealing and timing beat spraying. Everything that works happens outside and early; almost everything that backfires happens inside and late. We covered the basics a few years ago in Dealing with Boxelder Bugs; here is the step-by-step for a valley home.
What works
- Vacuum, don’t crush. Use a shop vac for big clusters on the siding or in the attic, or slide a knee-high stocking into the hose of a household vacuum so the bugs collect in the stocking instead of the bag.
- Wash them off the wall. On a cool morning, a hard spray of water, or water with a little dish soap, knocks the mass off the siding before the bugs work their way in.
- Seal the sunny side first. Caulk around window frames and trim, fill gaps where siding meets the foundation and where utility lines enter, replace torn screens on attic, gable and crawl space vents, and add door sweeps. Do the south and west walls first. The full list is in our fall pest-proofing checklist.
- Treat the exterior at the right time. An exterior application to the sunny walls, eaves and entry gaps in late September to mid October, before the bugs move inside, cuts the number that make it into the walls. Once they are in, an exterior treatment does little.
What backfires
- Spraying inside. Interior sprays kill only the bugs you hit and do nothing about the hundreds still in the wall void, and they leave residue where you live. We do not do it, and we do not recommend it.
- Foggers. A fogger cannot reach into a wall void, which is where the bugs are.
- Cutting down the tree first. Removing a female boxelder right against the house can help, but the bugs fly up to two miles, so a tree on the next street can still stock your walls. Treat it as a last resort.
Why Salem and Dallas neighborhoods see so many
We have the trees, the sun exposures and the housing stock that boxelder bugs like best.
Big-leaf maples line the older streets of Salem and Keizer, planted boxelders turn up in yards, parks and along creeks, and ash trees fill in the low, wet ground. On the farm edges around Dallas and Monmouth, orchards and windbreaks add more hosts, since in heavy years the bugs also feed on ripening fruit.
Housing does the rest. Ranch homes from the 1950s through the 1980s have lap siding, wide eaves and original windows, and a west-facing wall with light paint and no shade is close to ideal. Then our mild winters, with long stretches between 35 and 50 F and frequent sunny breaks, wake the bugs repeatedly, so valley homeowners see them indoors all winter instead of once in spring.
When to call a professional
Call when the bugs are coming inside by the dozens, when they return every year in spite of sealing, or when you want the exterior treatment timed right the first time.
Our inspection identifies the walls the bugs are using, the gaps they enter through, the host trees nearby, and the condition of your attic and soffit vents. We then time an exterior application to the window before they enter, using EPA-registered products applied according to the label, and we tell you exactly what to expect, including any re-entry times. Family- and pet-considerate options are available, and inside the house we rely on removal and sealing rather than spraying your living space. Read more about our boxelder bug control service. AAA Pest Exterminators has been family-owned and operated in Salem since 1997, with no long-term contracts.
Frequently asked questions
Do boxelder bugs bite?
Not as a rule. They feed on plant seeds and have no interest in people or pets. The National Pesticide Information Center notes they are generally not known to bite, with only rare reports of a defensive nip, and they do not sting or spread disease. The real complaints are numbers, stains and the sight of them on the window in January.
Why are boxelder bugs in my house in January?
They have been in your walls since October. A run of sunny winter days warms the siding, and some of the overwintering adults follow the heat inward through gaps around windows, light fixtures and baseboards. Vacuum them up. Nothing is hatching, and the same bugs will head back to the trees in spring.
Should I cut down my boxelder tree?
Only as a last resort. A female, seed-bearing boxelder right against the house can be the main source, and removing it may help. But the bugs can fly up to two miles from a host tree, so a neighbor’s tree can keep your walls stocked. Sealing and a well-timed exterior treatment are the better first moves.
When is the best time to treat the outside of my house?
In the Willamette Valley, late September through mid October, once the bugs start gathering on the sunny walls but before cold nights push them inside. Earlier, and the treatment fades before the migration. Later, and the bugs are already in the walls, where no exterior treatment reaches them.
Pests in the nest? Don’t stress. Call the best.
Family-owned and operated in Salem since 1997. No long-term contracts. Serving Salem, Keizer, Albany, Dallas, Woodburn and McMinnville.
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