Every fall, the same scene plays out in thousands of homes across Quebec: dozens, sometimes hundreds, of ladybugs show up on windows, on sun-facing exterior walls, and then indoors.
In reality, this is a perfectly predictable behaviour — and one that’s easier to deal with before the ladybugs get in than after.
The vast majority of these fall invasions are caused by the Asian lady beetle (Harmonia axyridis), an introduced species that now dominates much of Quebec’s territory.
It’s noticeably larger than native ladybugs, with colouring that ranges from pale yellow to almost black and anywhere from 0 to 20 black spots. The most reliable way to identify it: an M- or W-shaped mark just behind the head, with two white patches beside it.
As winter approaches, Asian lady beetles look for a warm place to spend the cold season. They gather by the thousands on sun-exposed walls, usually facing south or west, before slipping through the smallest crack or gap.
Once the first group finds a good spot, it releases an aggregation pheromone that draws in the others. That’s why a house affected one year tends to be affected again, in the same spot, the following autumns.
When disturbed or crushed, the Asian lady beetle releases a foul-smelling yellow-orange fluid, a defence reflex that can stain curtains, walls, and fabric. It doesn’t sting, though it may nip slightly if handled directly.
It doesn’t pose a significant health risk, but a buildup of carcasses and residue can become an irritant, particularly for people sensitive to allergens.
The cleanest way to get rid of them indoors is to vacuum them up rather than crush them, then immediately empty the bag or canister outside so they can’t escape back in. Aerosol insecticides used indoors don’t address the source of the problem, the opening they came in through, and often leave carcasses hidden behind the walls.
The right time to act is now, before the fall’s mass arrival. That means sealing cracks around windows, roof flashing, dryer vents, and outdoor electrical outlets, especially on sun-facing walls, checking the condition of screens and door sweeps, and, for recurring cases, considering a perimeter treatment applied by a professional before the invasion peaks.
The cracks and gaps that let ladybugs in are often exactly the same ones that let mice in around the same time of year. A sealing inspection done for one problem usually helps prevent another: closing up the house before fall is really one and the same job, no matter which pest prompted the call.
Ladybugs already piling up on your windows or exterior walls? An inspection can identify entry points and help you act before the invasion grows.
