Why Mice Invade Quebec Homes Every Fall — And How to Stop Them

Published March 11, 2026 · Extermination DMP

As soon as nights in Quebec dip below 10 °C, mice start looking for a warmer place to spend the winter. Your house, with its steady heat, available food, and sheltered walls, is the perfect target. Every fall, exterminators across the Greater Montreal region — from Longueuil to Laval — see a sharp spike in rodent calls. Understanding why mice come in and how they do it is the first step toward keeping them out.

Why Fall Is Peak Season

The common house mouse (Mus musculus) and the deer mouse (Peromyscus maniculatus) are the two species most often found inside Quebec homes. Neither species hibernates. When outdoor food sources shrink and temperatures fall, mice follow warmth gradients — literally feeling their way toward the heat that escapes through gaps in your foundation, soffits, and utility lines.

A single mouse can squeeze through a hole the diameter of a dime. That means a tiny crack where a gas line enters your basement or a gap under a garage door is more than enough to grant access.

The Damage They Cause

Mice are not just a nuisance. They chew electrical wires, creating a genuine fire hazard. They contaminate pantry items with droppings and urine. And deer mice can carry hantavirus — rare in Quebec, but a serious respiratory threat if present. Mice also reproduce at an astonishing rate: a single pair can produce up to 60 offspring in one year under favourable conditions.

How to Mouse-Proof Your Home Before October

1. Seal the exterior. Walk the perimeter of your foundation with a flashlight. Fill cracks with steel wool backed by caulk — mice cannot chew through steel wool.
2. Check utility penetrations. Where plumbing, electrical conduit, and gas lines enter the house, ensure gaps are sealed with fire-rated foam or metal flashing.
3. Install door sweeps. Garage doors and side doors are common entry points. A quality brush or rubber sweep eliminates the gap.
4. Trim vegetation. Bushes and woodpiles against the house provide cover. Keep a 30 cm clearance around the foundation.
5. Store food properly. Transfer pet food, birdseed, and pantry staples into glass or metal containers with tight lids.

When Exclusion Is Not Enough

If you are already hearing scratching in the walls or finding droppings under the kitchen sink, exclusion alone will not solve the problem — the mice are already inside. A licensed exterminator will set up a strategic bait-and-trap program, identify every entry point, and seal them permanently once the population is eliminated. At Extermination DMP, we typically resolve a standard residential mouse infestation within two to three service visits.

A Note About Poison and Pets

Over-the-counter rodenticides pose a risk to pets and children. If you have cats, dogs, or toddlers, always let a professional select and place tamper-resistant bait stations in locations that are inaccessible to non-target animals.