Field plate · Halyomorpha halys
Brown marmorated stink bug
Shield-shaped, mottled brown, with pale bands on the antennae. The classic October invader of warm, south-facing Erie walls.
Plate 6 of 28. Drawn in profile to the identification marks named below; the scale rule is a drawing convention — sizes are given in the text.
Identification marks
Shield-shaped body about 14–17 mm long, mottled brown-grey. Two pale bands on each antenna and alternating light and dark bands around the edge of the abdomen — the bands are the field mark that separates it from native stink bugs.
Look-alikes it is confused with
Native brown stink bugs and rough stink bugs (no clean antennal bands), and the western conifer seed bug (longer, leaf-like hind legs, no shield outline).
Where it hides in a house
From late September it gathers on sunny exterior walls, then works into window frames, soffits, attics, and the voids behind siding. Indoors it wanders out on warm winter days and dies in light fixtures and window wells.
Health & property risk, stated plainly
A nuisance pest, not a biting or disease pest, and it does not breed indoors or damage the structure. Crushed bugs release the sharp, coriander-like odour that gives stink bugs their name, and large attic aggregations can stain and smell.
What actually works
Exclude first: caulk window and siding gaps, repair screens, fit door sweeps before the September flights. Vacuum indoor strays into soapy water and empty the vacuum promptly. Careful sealing of the south and west walls does the real outdoor work. Indoors, the one trap with evidence behind it is a foil pan of soapy water set under a lamp at night, for bugs already inside — outdoor light traps are not a control and exterior light only draws more bugs to the house.
What doesn't
Fogging the attic or spraying the walls indoors — it kills the bugs you can reach, leaves carcasses that feed other pests, and does nothing about the gaps the next warm afternoon will refill.
When to call a licensed pro
Call a pro when numbers in the attic are in the hundreds, when high exterior walls need treatment you cannot safely reach, or when exclusion work on a tall pre-war house is beyond a ladder you trust.