Quick answer: Stink bugs in the house each fall are a Willamette Valley routine, and you have company all over the valley. The brown marmorated stink bug, an invasive species that reached Oregon around 2004, spends late September and October massing on sunny walls and slipping into attics and walls to overwinter. It does not bite or breed indoors. Vacuum the strays, seal gaps, and treat the exterior before they get in.
Key takeaways
- The brown marmorated stink bug was first found in the Portland area around 2004 and is now most prevalent in the Willamette Valley, according to Oregon State University.
- It overwinters as an adult inside attics, wall voids and window frames, which is why it appears on sunny walls in October and on your windows on warm winter days.
- White bands on the antennae, smooth shoulders and a striped edge on the abdomen separate it from native stink bugs and the western conifer seed bug.
- Crushing releases the odor; a vacuum with a stocking in the hose, or a lamp over a bowl of soapy water, clears indoor stragglers without the smell.
Why are there so many stink bugs in my house this fall?
Because the brown marmorated stink bug overwinters as an adult, and it picks buildings, especially sunny, light-colored ones, as the place to do it.
According to Oregon State University’s College of Agricultural Sciences, the brown marmorated stink bug arrived from Asia in the Portland area around 2004 and is now present in most Oregon counties, with the heaviest populations in the Willamette Valley. It feeds on a huge range of plants all summer, then heads for shelter when the nights turn cool.
The timing in Salem is predictable. On the first warm, sunny afternoons after a run of cool nights, usually the last week of September into mid October, adults pile onto south- and west-facing walls, window frames and eaves. By late October, according to Utah State University Extension, the adults have entered a winter resting state called diapause, and the bugs you see for the next five months are the ones already inside your walls.
Is it the invasive brown marmorated stink bug or a native one?
Look at the antennae. The brown marmorated stink bug has pale bands on each dark antenna, smooth rounded shoulders, and alternating light and dark bands along the edge of the abdomen. Native stink bugs and the common look-alikes lack that combination.
The EPA describes the adult as shield-shaped with brown mottling, 14 to 17 mm long, roughly the size of a dime.
| Insect | Size | Shape and color | Tell-tale detail | Comes indoors in fall? |
|---|---|---|---|---|
| Brown marmorated stink bug | About 5/8 inch | Wide shield, mottled brown | White bands on dark antennae, smooth shoulders, banded abdomen edge | Yes, often in large numbers |
| Consperse stink bug (native) | Slightly smaller | Brown shield; underside may be greenish | Light-colored antennae without bold bands | Rarely |
| Rough stink bug (native) | Similar size | Gray-brown, bark-like texture | Rough, toothed shoulders; antennae not banded | Rarely |
| Western conifer seed bug | About 3/4 inch | Long, narrow, brown | Leaf-shaped flares on the hind legs; loud buzz in flight | Yes, usually a few at a time |
| Western boxelder bug | About 1/2 inch | Narrow, black with thin red lines | Three red lines right behind the head | Yes, often in large numbers |
If your bugs are black and red rather than brown, you have boxelder bugs; see our guide to boxelder bugs in Oregon. The two pests use the same walls and the same gaps, and our boxelder bug service handles them together.
Where do stink bugs hide in the house in winter?
In the shell of the house, not the living space: attics, wall voids, soffits, window and door frames, behind shutters and siding.
They are not feeding or laying eggs in there. In diapause they sit nearly motionless; a December attic can hold hundreds you never see. Then a mild, sunny spell warms the wall, and a few dozen wake and head for light and heat: the living room window, a ceiling fixture, a lampshade.
Salem’s winters make this worse than it is in colder places. With long stretches between 35 and 50 F and frequent sunny breaks, valley homes get repeated wake-ups from November through March instead of one emergence in spring. In spring the survivors leave for good.
How to get rid of stink bugs in the house without the smell
Do not crush them. Vacuum them with a stocking in the hose or drown them in soapy water, and skip the indoor sprays.
- The stocking trick. Push a knee-high nylon into the vacuum hose, fold the top over the end and secure it with a rubber band. The bugs collect in the stocking; tie it off and put it in the outside trash. The EPA notes a vacuum can smell of stink bugs for a while afterward, which is what the stocking prevents.
- A dedicated shop vac for the attic and garage, emptied outdoors.
- The lamp-and-bowl trap. Utah State University Extension describes a simple indoor trap: a lamp left on in a dark room at night with a bowl of soapy water just below it. Bugs fly to the light, drop in and drown.
- Singles on the window can be flicked into a cup of soapy water or flushed.
- Skip foggers and indoor sprays. The EPA points out that insecticides applied indoors will not prevent more bugs from emerging from cracks once the spray dries, and they are not a solution for long-term management.
Fall stink bug prevention: seal these spots first
Sealing only works before the migration, so in the Willamette Valley that means finishing by mid to late September and touching up in early October. Our earlier post on preventing a stink bug problem covers the basics; here is the priority order we use on valley homes.
- Windows and doors on the south and west walls. Caulk the frames inside and out, replace worn weather stripping, and add door sweeps wherever you can see daylight under a door.
- Siding and trim gaps. Fill the joints where lap siding meets corner boards and the foundation, and seal around outdoor faucets, dryer vents, cable and conduit entries.
- Attic, gable and soffit vents. Repair torn screens and add a screened cap to the chimney.
- Window air conditioners. Remove them for the season or seal tightly around them.
- The garage. Check the door’s bottom seal and the weather stripping on the door into the house.
Then time the exterior treatment. An application to the sunny walls, eaves and entry points in late September to mid October, before the bugs move in, reduces the number that reach the walls. The same schedule protects against boxelder bugs and lady beetles, and our fall pest-proofing checklist lays out the whole weekend.
Why the Willamette Valley is stink bug central
Farms and trees. The crops this bug damages most in Oregon, hazelnuts, tree fruit, small fruit and vegetables, are all grown in quantity in Marion, Polk and Yamhill counties, and the deciduous trees it feeds on in summer line every valley town.
That is why homes on the farm edges around Woodburn, with orchards, nurseries and field crops out the back door, tend to see the heaviest fall flights. It is also why OSU tracks this insect so closely: it damages fruit and nuts by piercing them and sucking out the contents, which means real losses for valley growers.
There is good news on the farm side. The samurai wasp, a tiny parasite that lays its eggs inside stink bug egg masses, turned up near the Oregon border in 2015 and in Portland in 2016, and OSU reports it has since been found in Salem and Beaverton. It does not sting people and it will not empty your attic, but over time it should take some pressure off the orchards.
When to call a professional
Call when the bugs are coming inside daily, when they return every fall, or when you want the exterior treatment timed to the migration instead of guessed at.
Our inspection maps the walls the bugs are using, the gaps they enter through and the condition of your vents and screens. We then schedule an exterior application to those walls, eaves and entry points in the late September to mid October window, using EPA-registered products applied according to the label, and we tell you exactly what to expect, including any re-entry times. Inside the house we rely on removal and sealing advice rather than spraying your living space, and family- and pet-considerate options are available. Read more about our stink 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 stink bugs bite?
No. Brown marmorated stink bugs feed on plants through a straw-like mouthpart and do not bite people or pets, sting, or feed on anything in the house. The problems they cause indoors are their numbers, the odor when they are crushed or vacuumed, and the clumsy buzzing flights into lamps on winter evenings.
Does killing a stink bug attract more of them?
Not in the way people fear. Utah State University Extension explains that the bugs gather on a building in response to pheromone cues, while the odor released when one is disturbed is a separate defensive chemical. Sun-warmed, light-colored walls and open gaps are what draw the crowd. Crushing them is still a bad idea because the smell lingers.
Why do stink bugs come back in February?
They never left. Adults that entered your walls and attic in October rest there in diapause. A run of mild, sunny days, which Salem gets most winters, warms the wall and stirs some of them toward light and heat, so they turn up at windows and lamps. Vacuum them; the rest leave on their own in spring.
Will stink bugs hurt my garden or hazelnut trees?
They can. Oregon State University reports that this bug feeds on vegetables, pears, apples and hazelnuts, leaving mushy brown spots inside fruit. In a backyard, hand-picking into soapy water and covering ripening crops help. Commercial growers rely on monitoring and on the samurai wasp, an egg parasite OSU has been releasing and tracking around the valley.
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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