Why mice come indoors every October in Edmonton

13 September 2026 · 6 min read

The trigger is temperature, not food

Mice do not decide to move indoors because your kitchen is untidy. They move because the ground temperature drops and a heated building is the nearest thing to survivable. Edmonton's first hard frost typically lands somewhere between late September and mid-October, and rodent calls climb sharply in the two to three weeks that follow.

That predictability is useful. It means the window for prevention is now, not once you hear scratching.

How small a gap actually matters

An adult house mouse can pass through a gap around 6mm wide - roughly the diameter of a pencil. A young one needs less. This is why sealing works and why casual inspection usually misses the entry point: you are not looking for a hole, you are looking for a gap.

Where they get in on Edmonton houses

• Where utilities enter the building - gas line, water line, electrical conduit, air conditioning line set. The drilled hole is almost always larger than the pipe.
• Weeping tile and foundation penetrations, particularly on older homes where the foundation has settled.
• Garage door seals. The rubber sweep perishes and lifts at the corners. An attached garage is effectively part of the house.
• Dryer and bathroom vents where the exterior flap has broken off or seized open.
• Under the bottom row of siding, especially where a deck or raised bed sits against the wall.

Why trapping alone does not end it

Trapping removes the mice currently inside. It does nothing about the gap that let them in, so the building refills. If you are catching mice week after week through November, you do not have a trapping problem - you have an unsealed building.

What you can do yourself this month

• Walk the exterior perimeter and look at every point where something enters the wall
• Replace a perished garage door sweep
• Move woodpiles, compost and stored materials away from the foundation
• Remove bird feeders and clear spilled seed from the ground
• Keep kitchen and bathroom surfaces clean and grease-free
• Store pet food and birdseed in sealed containers, not paper sacks in the garage

When to call someone

Call if you are hearing movement inside walls or ceilings, finding droppings in more than one room, or seeing gnaw damage on wiring. Wiring damage in particular is worth acting on quickly - it is the failure mode that turns a nuisance into a fire risk.

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Dealing with mice now? See mice and rodent control, download the mice preparation sheet, or call 780-707-1686.