How to prevent stink bugs from entering?
At a Glance
- Short answer: Sealing cracks, screening vents, and weatherstripping doors genuinely keeps brown marmorated stink bugs out — multiple land-grant sources call it the best method available — but it has to happen before they mass on your walls in early-to-mid September.
- Invader: Stink bug (BMSB)
- You’re likely in: Entry
- The date that matters: Seal by late August; University of Georgia's guidance is to have all exclusion measures in place by mid-September.
What the calendar decides
2 of 4
phases where this action still helps
Entry
the phase most readers are in
Oct 19–29
Manchester first hard frost (NOAA)
Stink bug (BMSB)
the invader this answer is about
The Invasion Window
The same action is right in September and useless in December. Find where you are on the year, then read the honest verdict for that phase.
sealing gaps and screening vents to prevent stink bug entry
August → mid-September
Seal cracks to the 3 mm slit / 7 mm hole standard around windows, doors, and siding; screen every attic and soffit vent; weatherstrip doors; cover window AC units.
This is the only window where prevention really works — stink bugs are still outdoors, and every gap closed now is one less way in when they start looking for a place to overwinter.
mid-September → first hard frost (~Oct 19–29 in Manchester)
Finish sealing as quickly as possible — University of Georgia advises having exclusion measures in place by mid-September, which is right at the edge of this window.
Stink bugs are actively massing and probing entry points on warm afternoons, so you're racing them — real value remains, but the ones already inside are already inside.
first hard frost → February
Stop sealing interior gaps. Vacuum any stink bugs that appear indoors — gently, since they release odor when disturbed — and put the bag outside.
Stink bugs that made it in are dormant in diapause inside wall voids. Interior insecticide application here is not recommended and risks leaving carcasses that feed carpet beetles and dermestids in the void.
Actively makes it worse
February → April, on the first warm sunny days
Vacuum stink bugs collecting at sunny windows. Don't seal interior gaps now — that only blocks their way out.
This is last fall's stink bugs reactivating and heading toward light to exit, not a new wave trying to get in.
You are probably in the Entry phase.
The only thing that reliably keeps stink bugs out is sealing them out before mid-September. No spray inside the house does it — and spraying inside actually makes things worse.
They are entering now, on warm afternoons. Last-call sealing still helps — but you are racing the first frost.
Seal by late August; University of Georgia's guidance is to have all exclusion measures in place by mid-September.
The thing that actually works
The one intervention with real evidence behind it — and the honest limit on when it is worth doing.
Once stink bugs are already inside a wall void, sealing does nothing for them — Penn State and University of Maryland are both direct that interior insecticide application at that point is not a viable or recommended treatment. Sealing interior gaps after entry can also trap bugs inside the void rather than keep new ones out.
This is largely a homeowner caulk-and-screen job — measuring gaps, running a caulk bead, and stapling up vent screen doesn't require a contractor for a typical house. Where full exterior sealing is really difficult or impossible — complex rooflines, extensive siding gaps — a licensed exterior application timed to late summer 'may offer some minor relief,' per Penn State, as a supplement to sealing, not a replacement for it.
The full picture
Why sealing is the one method that has real evidence behind it
Brown marmorated stink bugs are one of the most-studied fall invaders precisely because they're a documented agricultural and nuisance pest across the country. That research is consistent: University of Maryland and Penn State Extension both state that mechanical exclusion — physically closing the gaps a stink bug's body can fit through — is the single best method for keeping them out of a structure. This isn't a hedge; it's the strongest, most repeatable claim in the entire hub.
What makes the guidance actionable rather than vague is a 2019 peer-reviewed study out of Virginia Tech that measured exactly how small a gap has to be. Researchers found stink bugs pass round holes around 7–8 millimeters and slits around 3–4 millimeters with some regularity, but essentially none get through a 3-millimeter slit or a 7-millimeter hole — about the width of a pencil lead. That's a real, measured threshold, not a guess.
Where to seal, and what to use
Work the whole envelope: cracks around windows and doors, siding seams, utility pipe penetrations (pack steel wool into the gap before caulking over it), gaps behind chimneys, and fascia and roofline joints. Screen every attic, soffit, and gable vent with fine insect mesh — stink bugs will use any of these the same way cluster flies and lady beetles do. Cover window air-conditioner units, which extension sources specifically flag as an overlooked entry route.
Silicone or silicone-latex caulk is the material of choice — it flexes with seasonal movement and holds a seal longer than a rigid filler. None of this requires specialized tools; a caulk gun, a staple gun for vent screen, and a stepladder for the higher spots cover most single-family homes.
What doesn't work, and why interior spraying backfires
It's worth saying plainly what this page is not recommending: spraying the inside of your house. Penn State and University of Maryland are both explicit that interior insecticide application against overwintering stink bugs is not a viable or recommended treatment — the bugs are dormant inside a void you can't reach with a spray bottle. Worse, if you do kill some, the dead bodies accumulate in the wall and become food for carpet beetles and other dermestids, trading a nuisance you could vacuum for a fabric pest you can't see.
Where a professional really helps is narrower than an indoor treatment: a licensed exterior application, timed to late summer before stink bugs mass, can offer what Penn State calls 'some minor relief' on homes where sealing the full exterior is difficult or impractical. That's a supplement to your own sealing work, not a substitute for it.
A homeowner job, mostly
For a typical single-family home, sealing against stink bugs is squarely DIY: measure the gaps you can see and reach, run a bead of caulk, staple up some vent screen, and weatherstrip the doors. No license or specialized equipment is required for any of it.
Where it stops being a weekend project is a complex roofline, extensive vent access at height, or a home where the exterior truly can't be fully sealed — that's where a contractor for the physical work, or a licensed pest-control operator for a timed exterior application, earns its keep. For most houses, though, a free Saturday and a tube of caulk are the real answer.
The honest line — Sealing cracks, screening vents, and weatherstripping doors genuinely keeps brown marmorated stink bugs out — multiple land-grant sources call it the best method available — but it has to happen before they mass on your walls in early-to-mid September.
Key takeaways
- Mechanical exclusion — sealing, screening, weatherstripping — is the single best-evidenced method for keeping stink bugs out.
- A peer-reviewed study found the real exclusion threshold: slits under 3 mm and holes under 7 mm, roughly the width of a pencil lead.
- This must be finished before stink bugs mass on walls, roughly early-to-mid September in Manchester.
- Interior insecticide application is not recommended and can backfire by leaving carcasses that feed carpet beetles.
- This is largely a homeowner caulk-and-screen job; a pro's narrow value is a timed exterior application where full sealing is impractical.
Timing it to Manchester's calendar
UNH Cooperative Extension puts brown marmorated stink bug massing on New Hampshire buildings at roughly September 1 through 20, well ahead of Manchester's first hard frost, which typically lands between October 19 and 29 (NOAA). That gives a real but narrow window — about six to eight weeks — between when sealing still matters and when the ground truly freezes.
If you're reading this because stink bugs are already massing on your siding, sealing this week still has some value for the stragglers, but the realistic expectation is that many are already finding their way in. Put late August on next year's calendar instead of waiting for the first bug on the wall to prompt the search.
The date the year pivots on
Manchester’s first hard frost lands ~Oct 19–29 (NOAA). Fall invaders mass on sun-warmed south and west walls in the weeks before it — which is why the fix only works when it is done early.
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Sealing works. We're the backup plan, not the plan.
A timed exterior application before stink bugs mass — supplementing your own sealing on the walls too hard to fully close.
Frequently asked questions
The one date that matters
Seal by late August; University of Georgia's guidance is to have all exclusion measures in place by mid-September.
In Manchester the first hard frost lands around October 19–29 (NOAA). Everything about fall invaders pivots on being ahead of that date — which is why we put it in your calendar instead of selling you a winter visit that can’t work.
- NH-licensed applicator · #782664
- Same-day service
- Family-owned since 2017
Countdown to first frost
Manchester, NH
- Late AugSeal now
Caulk and screen while they are still outdoors — the only move that truly prevents the problem.
- Sep 10UNH deadline
Cooperative Extension’s marker: have exclusion done before September 10th.
~6 weeks of lead time — seal here, not when they’re on your ceiling. - mid-SepEntry begins
They mass on sun-warmed south and west walls on warm afternoons and go in. The window is closing.
- Oct 19–29First hard frost
Manchester’s NOAA frost window. After this they are dormant in the walls — no spray reaches them.
Sources(5)
- [1]University of Maryland Extension — Tips for Dealing With Brown Marmorated Stink Bugs
Mechanical exclusion as the best method; interior spray not viable or recommended
extensionverified 2026-07-16 - [2]Penn State Extension — Brown Marmorated Stink Bug
Mechanical exclusion best method; exterior application as minor supplement; carpet-beetle backfire risk
extensionverified 2026-07-16 - [3]Chambers, Kuhar, Reichard, Leskey, Pearce (2019), Journal of Economic Entomology 112(3):1343–1347
Peer-reviewed gap-size exclusion threshold: slits under 3 mm, holes under 7 mm
academicverified 2026-07-16 - [4]University of Georgia IPM — Brown marmorated stink bug
Exclusion measures in place by mid-September; diapause behavior
extensionverified 2026-07-16 - [5]UNH Cooperative Extension — Seasonal Insect Invaders in New Hampshire Homes
NH-specific BMSB massing window (Sept 1-20) on south/east/west walls
extensionverified 2026-07-16
Written & reviewed by
VerifiedDaniel Brady
NH-Licensed Pesticide Applicator · License #782664 (NHDAMF, RSA 430)
Daniel Brady is the New Hampshire–licensed applicator behind Anchor Pest Services, a family-owned pest control company serving the Manchester area since 2017.
Last updated 2026-07-16
Straightforward pest answers for New Hampshire homes
Seal What You Can. Call Us for the Rest.
Sealing cracks and screening vents against stink bugs is largely a homeowner job, and we'll say so plainly instead of booking a service you don't need. What Anchor Pest Services adds is a timed exterior perimeter application in late summer and early fall, before stink bugs enter, on the south and west walls where they mass — a supplement where full sealing is actually difficult, not a replacement for your own caulk gun. Family-owned since 2017, NH license #782664, serving Manchester, Nashua, Concord and nearby towns.
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