Identification
The western conifer seed bug (Leptoglossus occidentalis) is a large North American true bug that has spread to Quebec from the Pacific coast. It invades homes en masse in the fall to overwinter in the warmth, then tries to get back out in spring. It does not sting, does not bite, does not reproduce indoors, and does not damage structures.
A harmless invasion
Despite its impressive size (up to 20 mm), the western conifer seed bug is completely harmless. It feeds only on conifer seeds in summer and stays in diapause all winter inside walls or attics. Its only drawback is showing up in large numbers, along with the faint fruity scent it gives off when disturbed.
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ALarge brown body with flared tibiae
A large true bug 16 to 20 mm long, greyish brown. The hind tibiae are flattened and widened into a leaf shape, a feature unique to this species. Very visible and impressive, but harmless.
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BZigzag band across the abdomen
A characteristic white zigzag band across the abdomen, visible from above and from below. A distinctive sign that tells it apart from the brown marmorated stink bug.
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CPine smell when disturbed
Gives off a pleasant fruity smell (apple, pear) when picked up or disturbed. Unlike the brown marmorated stink bug, whose smell is strong and very unpleasant.
Adult
Feeds on conifer seeds (pine, fir, spruce) in the wild. Indoors it does not feed and stays in diapause. Gathers in large groups to overwinter.
Life cycle
HEMIMETABOLOUS · 3 STAGES · ANNUAL CYCLEReproduces exclusively outdoors on conifers in summer. The nymphs go through 5 stages from June to August. It never reproduces indoors.
Feeds on conifer seeds. Builds up reserves for hibernation. Starts looking for warm shelter as soon as the first cool nights arrive in September.
Enters diapause inside walls, in the attic, or in hidden spaces. Inactive in cold weather. Becomes active again during warm spells in winter and is often found in living areas.
Don't confuse it with
The western conifer seed bug is regularly confused with the brown marmorated stink bug, since both invade homes in the fall. Their shape and their smell are clearly different, however.
Signs of activity
Massive fall invasion
Large brown insects (16 to 20 mm) suddenly appearing in numbers on sunlit exterior walls in September and October. They come in through cracks and openings to overwinter.
Isolated individuals in winter
Isolated bugs found in living areas during mild spells in winter. They come out of diapause temporarily. They are slow and easy to catch.
Spring resurgence
Mass attempts to get out in March and April as temperatures climb. Found near windows and doors, trying to get back to the conifers to breed.
A massive invasion in September and October means the home sits close to mature conifers. The pressure does not go away on its own: as long as the entry points are not sealed, it happens again every fall.
Treatment
Soapy water trap for mass capture
- 2 L Warm water and 2 tbsp of dish soap The soap breaks the surface tension and drowns the bugs that fall in
- Fill a shallow basin with the soapy solution. Place it near a basement window, a light source, or the entry points you have identified. The bugs that come out fall in and drown. Replace the solution every week through the emergence season.
The western conifer seed bug (Leptoglossus occidentalis) gives off a pine or pine-cone smell when disturbed - unlike the brown marmorated stink bug, which smells of cilantro. This distinctive trait helps with identification.
The western conifer seed bug does not sting, does not bite, and does not transmit disease. It is only a nuisance. It does not reproduce indoors and dies if it is not put back outside.
These bugs gather by the dozen or by the hundred in attics, inside walls, and in cracks to overwinter. A single opening can let a whole group slip in during the fall.
Spotting the entry points
Identify how the bugs get into the building
Watch the south- and west-facing exterior walls in September and October at sunset: that is where the bugs gather while looking for entry points.
Inspect window frames, siding joints, cable penetrations, and soffits to identify the cracks used as access points.
Check for large conifers (pines, firs, spruces) within 50 metres: the more there are, the stronger the invasion pressure in the fall.
Prevention
- Caulk before mid-September
Seal every opening in the exterior envelope before the second week of September: window frames, siding joints, cable penetrations, soffits. The invasion season is short, but the pressure is intense.
ZONE 1 - EXTERIOR ENVELOPE
Frequently asked questions
What is the western conifer seed bug?
A large elongated brown bug (Leptoglossus occidentalis) with widened hind legs; it feeds on conifer seeds and is harmless to the home.
Is it dangerous?
No: it does not sting and causes no damage to the building. When disturbed, it can give off a smell and buzz loudly in flight.
Why does it come into my home?
Like other bugs, it seeks out warmth in the fall and slips in through the cracks and openings of sunlit walls to overwinter.
How do I keep it out?
Seal cracks, window frames, and soffits before fall, and vacuum up the ones already inside. A perimeter treatment by an exterminator helps as prevention.