The first one usually shows up in September, walking slowly across a window frame as though it has every right to be there. By late October there are a dozen, and one has landed on the TV.
The insect is almost certainly the brown marmorated stink bug, Halyomorpha halys. This page covers what it is and what it does. If you want the practical answer, it is on the removal page, and the trap question has its own page with the actual research.
Why They Come In
They are not hunting for crumbs. They are looking for somewhere to spend the winter.
Penn State Extension reports that brown marmorated stink bugs begin entering structures starting in September through October, in search of overwintering sites. University of Kentucky Extension gives early-to-mid September for Kentucky and notes that they gather on windows, doors, roof flashing, vents, fascia and siding, with a preference for the upper areas of buildings.
That last detail explains a lot. If your problem is worst in an upstairs bedroom or an attic, that is not coincidence, and it tells you where to look for the gaps.
Nothing about your housekeeping caused this. There is no food source indoors that draws them, because they do not feed indoors at all. They are responding to temperature and to the shape of your building.
Which Bug Is It
Two distinctions matter, and both get muddled constantly.
Brown marmorated stink bug versus native stink bugs. Halyomorpha halys is an introduced species from East Asia. Penn State Extension reports it was first collected in Allentown, Pennsylvania in 1998, although it probably arrived several years earlier. Native stink bugs exist and are common — Virginia Cooperative Extension names the brown stink bug Euschistus servus, the green stink bug Acrosternum hilare, the harlequin bug Murgantia histrionica, and the spined soldier bug Podisus maculiventris, which is a predator that feeds on other insects and is generally a good thing to have in a garden. Not every shield-shaped bug is the invasive one, and the one that piles into houses in numbers usually is.
Stink bugs versus the other fall invaders. Three other insects come indoors in the same weeks and get called stink bugs by people who have every reason not to know the difference. They are covered on their own pages, and the section below is a quick triage.
Identification
Penn State Extension gives the adult as approximately 17 mm, about two-thirds of an inch, shield-shaped and almost as wide as it is long. Three marks separate it from the native species:
- Lighter bands on the antennae. This is the single most useful feature and the easiest to see. Alternating pale and dark rings near the tip.
- Darker bands on the membranous overlapping part of the wings at the rear of the body.
- Patches of coppery or bluish-metallic punctures on the head — small rounded depressions that catch the light.
“Marmorated” means marbled, and that is a fair description of the mottled brown you see from above.
The Smell
University of Kentucky Extension describes it as a pungent, cilantro-like odor, produced by scent glands on the mid-section of the body. Penn State Extension locates those glands on the upper surface of the abdomen and the underside of the thorax.
It is released when the insect is picked up, disturbed, crushed, squeezed or handled. That is the practical rule: the smell is a response to interference, so the way to avoid it is not to interfere. Do not swat one. Do not step on one. Kentucky Extension also advises against touching your face or eyes after handling them.
Whether people find the smell unbearable or merely odd varies a great deal, and both reactions are normal. Virginia Tech researchers have described homeowners finding thousands of these cilantro-smelling bugs in their houses, which gives a sense of the scale the problem can reach in a bad year.
What They Do and Do Not Do
They do not bite
University of Kentucky Extension states that stink bugs are solely plant feeders and do not bite humans or pets. The mouthparts are a stylet built for piercing plant tissue and drinking plant juices.
They do not damage the house
Penn State Extension states that the stink bug will not reproduce inside structures or cause damage. They do not chew wood, they do not eat fabric, they do not nest.
They do not breed indoors
University of Kentucky Extension is specific: the adults overwinter in an unmated condition and do not breed or reproduce indoors. This is worth internalising, because it changes what you are dealing with. The population inside your walls is a fixed number that arrived in the fall and will not grow. It is a finite problem.
What they do damage is crops
This is where the species earns its reputation. Penn State Extension reports that feeding on tree fruits such as apples produces a characteristic distortion called “cat facing” that renders the fruit unmarketable. Virginia Tech’s Thomas Kuhar has listed apples, peaches, grapes, soybeans, peppers, tomatoes, corn and cotton among the crops documented as hosts.
Kuhar has also said that brown marmorated stink bug populations have pretty much stabilized in the mid-Atlantic states, with natural enemies and other factors keeping them somewhat regulated (as of October 2023). That is a statement about a moving population, which is why it carries its date.
The Other Fall Invaders
If the thing on your window does not match the description above, it is probably one of these three. Misidentification is the actual problem most people have, because the four insects arrive in the same weeks for the same reason and look nothing alike once you know what to look at.
- Black with thin red or orange lines, about half an inch — boxelder bug. Narrow, not shield-shaped.
- Round, orange or red, spotted, about a quarter inch — multicolored Asian lady beetle, which is not the native ladybug and behaves very differently.
- A slow, dark fly slightly larger than a house fly — cluster fly. Sluggish, and not a filth fly.
What to Do
The short version, with the detail on the removal page:
- Seal, do not spray. Exclusion is the only measure that reduces next year’s number.
- Vacuum the ones already inside, with the caveats about odor and vacuum choice that the removal page covers.
- Do not use insecticide indoors. Penn State Extension advises against it, and the reason is carpet beetles feeding on the dead insects.
Questions
Why are there suddenly stink bugs in my house?
They are looking for somewhere to spend the winter, not for food. Penn State Extension reports that brown marmorated stink bugs start entering structures in September through October in search of overwintering sites. University of Kentucky Extension gives early-to-mid September for Kentucky. Nothing in your house attracts them and nothing you cleaned would have prevented it; they are responding to falling temperatures, not to your kitchen.
Do stink bugs bite?
No. University of Kentucky Extension states that stink bugs are solely plant feeders and do not bite humans or pets. Their mouthparts are built to pierce plant tissue and drink plant juices, and they have no interest in and no equipment for biting people.
What is the smell, and what triggers it?
University of Kentucky Extension describes it as a pungent, cilantro-like odor produced by scent glands on the mid-section of the body. Penn State Extension locates those glands on the upper surface of the abdomen and the underside of the thorax. It is released when the insect is picked up, disturbed, crushed, squeezed or handled — which is the whole argument against swatting them.
Will stink bugs damage my house or breed inside it?
No to both. Penn State Extension states plainly that the stink bug will not reproduce inside structures or cause damage. University of Kentucky Extension adds that the adults overwinter in an unmated condition and do not breed or reproduce indoors. The ones you see in March are the same individuals that came in during September, not a new generation.
How do I tell a brown marmorated stink bug from a native stink bug?
Look at the antennae and the head. Penn State Extension describes the brown marmorated stink bug as having lighter bands on the antennae, darker bands on the membranous overlapping part of the wings at the rear, and patches of coppery or bluish-metallic punctures on the head. It is about 17 mm, roughly two-thirds of an inch, and almost as wide as it is long. Native stink bugs are real, common and mostly not the ones coming indoors in numbers.
Where did the brown marmorated stink bug come from?
East Asia — China, Japan and Korea. Penn State Extension reports it was first collected in Allentown, Pennsylvania in 1998, although it probably arrived several years earlier. StopBMSB, the USDA-funded research project, reported that as of 2021 it had been detected in 47 states and 4 Canadian provinces.
Should I spray insecticide indoors to stop them?
Penn State Extension advises against it: it is not advisable to use an insecticide inside after the insects have gained access. Both Penn State and University of Kentucky Extension give the same reason — dead insects inside wall voids become food for carpet beetles, which then damage woolens and stored goods. You would be trading a harmless nuisance for a destructive one.
Sources
- Penn State Extension (Skvarla; originally Jacobs). Brown Marmorated Stink Bug. Updated June 24, 2026. https://extension.psu.edu/brown-marmorated-stink-bug
- University of Kentucky Entomology (Potter and Bessin). Stink Bug Infestation of Dwellings (ENTFACT-654). Revised March 2026. https://entomology.ca.uky.edu/ef654
- Virginia Cooperative Extension (Bekelja and Day). Stink Bugs (444-621 / ENTO-517NP). Accessed August 21, 2026. https://www.pubs.ext.vt.edu/444/444-621/444-621.html
- StopBMSB.org, Northeastern IPM Center / USDA NIFA. Where Is BMSB?. Accessed August 21, 2026. https://www.stopbmsb.org/where-is-bmsb/
- Virginia Tech News (Thomas Kuhar, Department of Entomology). Stink bugs: The good, the bad, and how to get rid of them. October 27, 2023. https://news.vt.edu/articles/2023/10/stink_bugs_expert.html