Identification
Adults are 12-17mm, shield-shaped, mottled brownish-grey with distinctive alternating light and dark bands on the antennae and the edges of the abdomen (visible when wings are folded). Underside is lighter. Nymphs are smaller, rounder, with red-black coloration and no wings. When crushed or disturbed, they release a characteristic cilantro-like odor from scent glands on the thorax — hence 'stink bug.' Native BC stink bugs exist (green stink bug, consperse stink bug) but are smaller, greener, and don't aggregate indoors. Halyomorpha halys is the species behind the vast majority of BC indoor stink bug calls.
Habitat in BC
Outdoors (summer): feeding on tree fruit (peach, pear, apple), vegetable crops (tomatoes, peppers, soy), and ornamentals. Lower Mainland and Fraser Valley agricultural areas see heavy seasonal pressure; the BMSB has been a priority pest for BC fruit growers since detection in Vancouver in 2015. Indoors (winter): aggregates in sheltered locations for overwintering — attics, wall voids, behind window casings, in unheated garages. Older homes with gaps in the envelope see heavy winter pressure. South-facing exposures are preferred entry points in October-November.
Signs you have brown marmorated stink bug
- Shield-shaped brownish bugs clustering on sunny exterior walls in September-October.
- Indoor bug sightings in late winter or early spring (February-April) as they emerge from overwintering.
- Cilantro-like smell when a bug is crushed or disturbed.
- Clusters in attics, inside window frames, or behind curtains.
- Agricultural damage on fruit trees or garden vegetables — distinctive sunken 'cat-facing' or dimpling on fruit.
Risk & damage
Human risk: minimal. BMSB doesn't bite, doesn't carry disease, doesn't damage structures. The odor from crushed bugs is unpleasant but not toxic. A secondary risk: some people are mildly allergic to the defensive compounds; heavy indoor populations can trigger respiratory irritation in sensitive individuals. Agricultural risk: high. BMSB causes significant crop damage to Fraser Valley stone fruit, apples, peppers, and tomatoes — the species is listed as an agricultural priority pest by the BC Ministry of Agriculture.
Seasonality in Metro Vancouver
Two distinct pressure windows in BC. Fall (September-November): outdoor adults seek overwintering sites and cluster on sunny exterior walls, entering buildings through gaps. This is the critical exclusion window. Winter: aggregated inside walls and attics, largely inactive. Spring (February-May): emerging adults become visible indoors as they try to exit; this is when most homeowner calls come in. Summer: outdoor feeding; indoor population typically near-zero.
Treatment approach
Exclusion before pesticide, always. BMSB is a stubborn chemical target — they have low insecticide susceptibility and spray-kill leaves dead bugs that decompose in wall voids, creating odor and beetle-larvae secondary pests. Step one: seal exterior entry points during summer (July-August) — weep holes, gaps around windows, attic vents, dryer vents, utility penetrations. Step two: reduce attractant conditions — trim vegetation away from south walls, upgrade window screens. Step three: for active indoor populations, a vacuum with sealed bag is the preferred removal method (don't crush — the odor). Step four (last resort): limited exterior residual treatment in late summer to knock back clustering populations before entry. We do not fog or treat attic voids with insecticide; dead-bug accumulation is worse than living-bug presence.
When to call a professional
For occasional winter-to-spring indoor sightings (5-20 bugs over a season), DIY vacuum removal plus summer exclusion work is sufficient. Call for professional service if: you have an active aggregation of 50+ bugs in an attic or wall, you need documented exclusion work for a strata building, you're an agricultural operator needing integrated BMSB management, or you're planning a reno and want to audit envelope gaps before sealing walls. Our BMSB exclusion service runs $495-$950 depending on home size and access.
Prevention playbook
How to prevent brown marmorated stink bug in Metro Vancouver homes
- 1
Seal exterior envelope gaps in summer
July and August — before BMSB starts seeking overwintering sites — walk the exterior and caulk every gap larger than 3mm around windows, doors, utility penetrations, siding joints. Screen all attic and soffit vents with metal insect mesh. This is the single highest-leverage BMSB prevention action.
- 2
Install tight-fitting door sweeps
BMSB squeeze under door thresholds with gaps as narrow as 3mm. Weather-resistant door sweeps on all exterior doors, including garage-to-house connecting doors.
- 3
Replace or upgrade old window screens
Screens with holes, poor fit, or standard rather than fine-mesh allow BMSB entry around window frames. Upgrade to tight-fit, intact screens before fall clustering season.
- 4
Prune vegetation from south walls
Trees and shrubs touching or overhanging south-facing exterior walls shelter BMSB during the warmer phase of autumn — trim vegetation back to at least 1m from the wall.
- 5
Use vacuums, not sprays, for indoor bugs
When you see indoor BMSB in winter or spring, vacuum them (with a sealed disposable bag) rather than crush or spray. Crushing releases odor; spraying creates dead-bug accumulation in wall voids that decomposes into secondary pest problems.
- 6
Agricultural: pheromone traps + monitoring
For Fraser Valley growers: BMSB pheromone traps (aggregation lure) placed around orchard perimeter for early-season monitoring. Commercial integrated BMSB management is outside the scope of this guide — contact BC Ministry of Agriculture for grower programs.
The Wild Pest service
See our Brown Marmorated Stink Bug treatment page
Transparent pricing, 60-day return guarantee, same-day response across Metro Vancouver. Every treatment is documented with photos and service notes.
Frequently asked questions about brown marmorated stink bug
Is the brown marmorated stink bug dangerous?+
Not directly. It doesn't bite, sting, or carry disease. The smell from crushed bugs is unpleasant but not harmful. Indirect concerns: very heavy indoor populations can trigger respiratory irritation in sensitive individuals, and in agricultural settings it's a significant crop pest.
Why do they suddenly appear in my house in February?+
They've been there since October. BMSB enters buildings in fall for overwintering, clusters dormantly in wall voids and attics through winter, and becomes active again in late winter or early spring as they try to exit. That's why the first warm sunny day in February often triggers dozens of indoor sightings.
Should I spray my house for stink bugs?+
Usually no. BMSB has low insecticide susceptibility, spraying creates dead-bug accumulation inside walls that causes secondary pest issues (carpet beetles feeding on dead bugs), and the real fix — exclusion — is cheaper and more durable. Professional exterior residual treatment has a place only as a late-summer supplement to exclusion work, not a replacement.
Are they invasive in BC?+
Yes. Halyomorpha halys is native to East Asia and was detected in Vancouver in 2015. It has since established populations across the Lower Mainland and Fraser Valley. The BC Ministry of Agriculture tracks it as a priority agricultural pest. Homeowner exclusion helps reduce local overwintering populations.
Related species