Bed bugs in old Montreal plexes: why they spread

Shared walls, century-old plaster, a century of cracks

A plex is, first and foremost, shared walls. Behind the plaster on wood lath, behind floors that have been shifting for a hundred years, behind baseboards that never sit quite flush, there are thousands of gaps. An adult bed bug is barely 5 mm long and slips into a crack the thickness of a credit card. To it, an old plex is a heated maze with a pantry included.

Add shared plumbing and ducts running vertically between units, and electrical outlets installed back-to-back on either side of a party wall. Bed bugs travel from one apartment to another without ever setting foot outside. When we inspect an infested unit in a plex, we very often find traces in neighbouring units — even when the neighbours haven't noticed a thing yet.

That's the trade's first lesson: in a plex, you never inspect just one unit. We always check the adjacent ones — above, below, and across the wall. It's the only way to stop the infestation from coming back three months later through the living-room outlet.

July 1st: peak infestation season

Every year around July 1st, tens of thousands of Montrealers move at the same time. The sidewalks of Mont-Royal Avenue, Saint-Laurent Boulevard and Villeray's streets fill up with abandoned sofas, dressers and mattresses. And every year, some of that furniture carries bed bugs.

A bed bug can survive months without feeding, tucked into a mattress seam or under a sofa leg. Picking up an upholstered piece off the sidewalk sometimes means inviting a full infestation home — without realizing it for weeks, while the colony grows large enough to be noticed.

Our golden rule, simple and non-negotiable: never pick up a mattress or upholstered furniture off the sidewalk. If you buy second-hand, inspect every seam with a flashlight before bringing it inside, and when in doubt, have it treated or walk away. A free sofa that costs you a full apartment treatment is no bargain.

What to inspect first in a plex

Suspect something? Here's the checklist we use ourselves on inspection, in order:

• Mattress and box-spring seams, with a flashlight: look for tiny black spots (droppings), translucent shed skins, and sometimes the insects themselves.
• The headboard and bed frame, especially joints and screws: their favourite hiding spot, centimetres from their food source.
• Baseboards and plaster cracks near the bed, plus the underside of nightstands.
• Outlets and switches on the shared wall: traces often turn up there first.

Found signs in more than one spot, or in a neighbour's unit too? That's a building-scale problem — see our guide to bed bugs in the Plateau, or call us: one coordinated treatment beats three separate ones every time.