Mice are among the most common pests in Canadian homes, and Ontario is no exception. They move in quietly — usually as temperatures drop — and by the time most homeowners notice them, a small problem has already become a significant infestation. A single female mouse can produce up to 60 offspring per year, which means a couple of mice in September can become dozens by January.

The key to controlling a mouse problem is catching it early. Here are the most common warning signs to watch for, and exactly what to do when you spot them.

Warning Signs of a Mouse Infestation

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Droppings

Mouse droppings are small (3–6mm), dark brown, and rod-shaped — similar to a grain of rice. You'll typically find them along walls, in cupboards, behind appliances, and under sinks. Fresh droppings are soft and dark; older ones turn grey and hard. The more droppings you find, the more active the infestation.

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Gnaw marks

Mice gnaw constantly to keep their teeth worn down. Look for chew marks on food packaging, wooden furniture, baseboards, electrical wires, and even plastic pipes. Fresh gnaw marks are light in colour; older ones darken over time. Chewed wiring is a serious fire hazard and should be addressed immediately.

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Scratching and scurrying sounds

Mice are most active at night. If you hear scratching, scurrying, or squeaking sounds coming from inside walls, above ceilings, or beneath floors after dark, there's a strong chance you have mice. These sounds are often loudest in the evening when the house is quiet.

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Nesting material

Mice build nests from shredded paper, fabric, insulation, and other soft materials. Check in the back of drawers, inside appliances, in storage boxes, and in wall cavities. A discovered nest means mice have been present long enough to settle in — and likely breed.

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Tracks and grease marks

Mice follow the same routes repeatedly, leaving greasy smear marks along walls and baseboards from the oil in their fur. In dusty or less-trafficked areas, you may also spot tiny footprints or tail drag marks. These trails help identify exactly where mice are travelling through your home.

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Pet behaviour changes

Cats and dogs often detect mice long before humans do. If your pet is suddenly fixated on a wall, cabinet, or area of the floor — scratching, pawing, or staring intently — take it seriously. Animals can smell and hear rodents through walls.

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Musty or ammonia-like odour

A heavy mouse infestation produces a distinct musky smell from urine and droppings. If you notice an unusual odour — particularly in enclosed spaces like cupboards, closets, or crawl spaces — it's worth investigating further.

Health Warning

Mouse droppings, urine, and nesting material can carry Salmonella. Always wear gloves and a mask when cleaning up rodent evidence, and never vacuum droppings — this can spread airborne particles. Use damp paper towels and disinfectant spray.

What To Do If You Spot the Signs

Step 1 — Don't panic, but act quickly

A single mouse sighting doesn't necessarily mean a full infestation, but it's always a sign that at least one mouse has found a way in. Early action prevents a small problem from becoming a large one.

Step 2 — Find and seal entry points

Mice can squeeze through a gap the size of a dime (6mm). Inspect your foundation, utility penetrations, garage doors, and any gaps around pipes. Seal openings with steel wool and caulk — mice cannot chew through steel wool. Don't forget to check under doors; a gap larger than 6mm is an open invitation.

Step 3 — Remove food and water sources

Store all food in airtight containers, including pet food. Empty garbage bins nightly, fix any leaky pipes, and eliminate clutter where mice can hide and nest. Reducing attractants makes your home far less hospitable.

Step 4 — Set traps strategically

Snap traps placed along walls (where mice travel) are highly effective. Bait with peanut butter or chocolate and set traps perpendicular to the wall with the trigger end facing the baseboard. Check and reset traps daily. For larger infestations, traps alone are rarely sufficient.

Step 5 — Call a professional

If you're finding droppings in multiple rooms, hearing activity in walls, or traps aren't resolving the problem within a week, it's time to call in a professional. A trained technician will identify the full extent of the infestation, locate entry points, apply targeted treatments, and seal vulnerabilities to prevent re-entry.

Willard's Tip

The biggest mistake homeowners make is waiting too long. If you're seeing signs in October or November, act immediately — winter drives rodents indoors in greater numbers and infestations grow rapidly in the colder months.

Why Professional Treatment Works Better

Store-bought poison bait and traps address the symptom, not the source. Without identifying and sealing entry points, new mice will simply replace the ones you catch. Professional rodent control includes:

Think you have a mouse problem?

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