Identification
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AMarbled brown shield-shaped body
A typically pentagonal body 12 to 17 mm long, brown with a characteristic marbled pattern. The edge of the abdomen alternates white and black bands. The scutellum (the dorsal triangle) is very visible.
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BBanded antennae and striped edge
Antennae with alternating white and black bands. The white and black striped lateral edges of the abdomen are a distinctive sign of Halyomorpha halys. No spines on the shoulders.
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CPowerful scent glands
Two glands under the thorax produce a chemical compound (trans-2-decenal) with a strong, lingering smell. Hard to remove from porous surfaces. Do not crush.
Adult
Highly polyphagous: it attacks more than 300 plant species. Indoors it enters diapause and does not feed. It gathers in aggregations that can reach hundreds of individuals.
Life cycle
The female lays 20 to 30 pale green eggs in clusters under leaves. Five nymphal stages from June to September. It reproduces exclusively outdoors on cultivated and ornamental plants.
Feeds actively on fruit, vegetables, and seeds. Causes serious damage to Quebec vegetable crops. Builds up reserves for overwintering.
They gather by the hundreds inside walls, attics, crawl spaces, and hidden voids. They release an aggregation pheromone that draws even more individuals the following year if they are not eliminated.
Signs of activity
Strong, lingering odour
A powerful, unpleasant smell (burnt cilantro, chemical mustiness) in a room or inside the walls. It can last several days on porous surfaces. The most distinctive sign.
Grouped fall invasion
Dozens or hundreds of marbled brown bugs on sunlit exterior walls in September and October. More numerous than other stink bug species. They come in en masse through cracks.
Active individuals on mild winter days
Slow, groggy bugs found in living areas during warm spells in winter. They can stain light-coloured surfaces if crushed. They prefer warm, well-lit areas.
Treatment
Odour-free capture solution with a DIY light trap
Crushing a brown marmorated stink bug releases a very persistent cilantro odour that attracts other bugs. Always pick them up with a piece of paper or vacuum them up so the scent response is not triggered.
The brown marmorated stink bug (Halyomorpha halys) is an invasive species from Asia. It reached Quebec around 2014. With no effective natural predator, populations grow every fall.
Vacuuming the bugs with a bagged vacuum cleaner is the most effective method. Empty the bag outside immediately into a sealed container so the smell does not stay in the vacuum.
Finding the entry points
Identify where they get through the building envelope
Watch the south- and west-facing exterior walls in late September: the brown marmorated stink bug gathers in large, visible groups before coming in. This is the best time to assess the scale.
Inspect the attic and roof space in October with a flashlight: look for aggregations of brown bugs in the corners, along the rafters, and around roof penetrations.
Identify the characteristic smell in walls or voids in winter: a cilantro or chemical odour at electrical outlets or switches points to an aggregation inside the wall.
Prevention
Frequently asked questions
What is the brown marmorated stink bug?
A marbled brown shield-shaped bug (Halyomorpha halys), an invasive species that gives off an unpleasant smell when disturbed.
Is it dangerous?
Not to people: it does not sting and does not bite. It is above all a nuisance and a pest of gardens and orchards.
Why does it come into my home in the fall?
It is looking for warm shelter for the winter and slips in through cracks, window frames, and soffits on sunlit walls, sometimes in large numbers.
How do I keep it out?
Seal cracks and gaps before fall, and vacuum up the ones already inside without crushing them. An exterminator can treat the perimeter as a preventive measure.