How do I recognize a stink bug infestation?

If you want a fast, reliable field ID rather than a guess based on general shape and color, three features do almost all the work. First, the antennae: on a true BMSB, the last two segments show an alternating dark-light-dark-light-dark banding pattern working in from the tip — UNH Cooperative Extension describes this precisely. Second, the 'shoulders' — the pronotum, the plate just behind the head — are smooth and rounded on BMSB, with no teeth or spines along the margin, which distinguishes it from several native look-alikes that do have toothed shoulders. Third, the exposed rear edge of the abdomen, visible from above when the wings are folded, shows the same alternating light-and-dark marmorated banding that gives the species its name. Add small metallic-green punctures across the head and pronotum, and a body length in the 12–17 millimeter range, and you have enough to distinguish BMSB confidently from the great majority of look-alikes without needing a lab identification.

Identification isn't just about the insect's body — where and when you see it matters just as much. UNH Cooperative Extension notes BMSB adults mass on building exteriors roughly from September 1st through the 20th in this region, overwhelmingly on south and west siding that holds the day's heat, before squeezing into cracks, vents, and siding gaps to overwinter. If what you're seeing indoors is happening in December, January, or a warm spell in February or March, it's worth knowing that this is very likely the same population that entered the previous fall, reactivated by warmth and moving toward windows and light — not a fresh invasion and not evidence that an earlier treatment failed. Recognizing that distinction changes what 'recognizing an infestation' should mean here: it's rarely a growing colony, because BMSB does not reproduce indoors.

Getting the ID right matters because not every shield-shaped bug on your siding deserves the same response. New Hampshire has roughly three dozen native stink bug species, several of them brown, and none carry BMSB's specific banded-antennae-plus-marmorated-abdomen combination — they're rarely home invaders in meaningful numbers. The western conifer seed bug is a distinct, related true bug that is also a genuine fall invader and equally harmless, identifiable by its more slender body and distinctively flattened, leaf-shaped hind legs; it isn't technically a stink bug, but the same seal-before-entry approach applies to it. Most importantly, some true bugs that superficially resemble stink bugs — including predatory species with a toothed or crested pronotum — are beneficial insects that hunt soft-bodied garden and orchard pests. Treating one of those as a pest problem removes something that was working in your favor.

Once BMSB is confirmed rather than assumed, the realistic playbook is straightforward and calendar-dependent: exterior exclusion — caulking siding cracks, screening vents, sealing gaps around windows and doors — done before the fall entry window closes is the one intervention with real evidence behind it. Once BMSB is already inside for the winter, vacuum whatever wanders into living space and never spray the wall void, since dead insects there feed carpet beetles and other secondary pests. The odor mechanism, the stain questions, and the exclusion timing details each get their own full treatment elsewhere on this hub and in the broader species library — this page's job is narrowly the ID, not re-deriving the whole control plan.