It's 11pm. You're lying in bed, about to fall asleep, and you hear it — scratching inside the wall behind your headboard. Light, fast, persistent. You hold your breath. There it is again.
That's mice. And if you're hearing them in one wall, there's a good chance they're already in others.
Mice don't just live in your walls — they travel through them, nest in them, and use the empty spaces behind your drywall as highways between your kitchen, bathroom, and anywhere else they can find food and water. In Toronto's older homes, especially in neighborhoods like the Annex, Leslieville, and Little Portugal, mice find easy access through foundation cracks, gaps around old pipes, and poorly sealed basement windows.
Here's how to tell if you've got mice in your walls, why they're there, and what to do about it.
Signs You Have Mice in Your Walls
1. Scratching, Scurrying, or Gnawing Sounds
This is the most obvious sign. Mice are nocturnal, so you'll hear them between 10pm and 4am. The sound is distinct from squirrels (which are louder and only active during the day) or settling house noises (which don't repeat in patterns).
If the scratching moves — say, it starts near your bedroom and then shifts toward the kitchen — that's a mouse traveling through the wall cavity.
2. Droppings Near Walls and Baseboards
Mouse droppings are small, dark, and pellet-shaped — about the size of a grain of rice. You'll find them along baseboards, in cupboards, under sinks, and near food sources. If you're finding droppings but not seeing mice, they're likely living in the walls and only coming out at night to forage.
3. Gnaw Marks on Baseboards, Drywall, or Wires
Mice chew constantly to keep their teeth from overgrowing. If you see fresh gnaw marks on baseboards, drywall corners, or exposed wires in your basement or attic, that's active mouse activity. Fresh marks are lighter in color; older ones darken over time.
4. Grease Marks Along Walls
Mice have oily fur. When they travel the same path repeatedly (which they do — mice are creatures of habit), they leave dark smudge marks along baseboards and wall edges. These are most visible on lighter-colored walls and in high-traffic mouse areas like behind the stove or along basement walls.
5. A Stale, Musky Smell
If the infestation is large or has been going on for a while, you'll start to smell it. Mouse urine has a distinct ammonia-like odor. It's strongest in enclosed spaces like closets, cabinets, and wall cavities with poor ventilation.
6. Your Pets Are Acting Strange
Dogs and cats can hear and smell mice long before you notice them. If your dog is suddenly obsessed with sniffing a specific wall or your cat is staring intently at the baseboard for hours, there's probably something in there.
Why Mice Are in Your Walls (and Why It Gets Worse in Winter)
Mice don't live outside year-round. They're opportunistic — they go where the conditions are best. In Toronto, that means inside your walls when the temperature drops.
Here's why:
Toronto's Housing Stock Is Old
Many GTA homes were built between the 1920s and 1960s, long before modern building codes required proper sealing and rodent-proofing. Older brick homes in neighborhoods like High Park, the Beaches, and Riverdale have foundation gaps, aging mortar, and unscreened vents that are easy entry points for mice.
Mice Can Fit Through Impossibly Small Gaps
A mouse can squeeze through a hole the size of a dime — about 6mm. That means gaps around pipes, utility lines, dryer vents, and foundation cracks are all potential entry points. Once inside your walls, they have free access to the rest of your house.
Walls Provide Shelter, Insulation, and Safety
From a mouse's perspective, your wall cavities are perfect: warm, dark, safe from predators, and close to food sources. They nest in insulation, shred paper and fabric for bedding, and travel between rooms through the hollow spaces behind drywall.
Winter Drives Them Indoors
Mice don't hibernate. When outdoor temperatures drop below 10°C, they start looking for indoor shelter. In Toronto, that means October through March is peak mouse season. If you're hearing scratching in your walls in November, you're not alone — we see a surge in calls every fall.
What to Do If You Have Mice in Your Walls
Step 1: Confirm It's Mice (Not Squirrels or Rats)
Timing matters. Mice are nocturnal. Squirrels are diurnal (daytime only). If you're hearing noise during the day, especially loud thumping or running, that's probably a squirrel in your attic or roof cavity — not a mouse in your walls.
Rats sound heavier and slower than mice. If the scratching sounds like something larger than a deck of cards moving around, you might be dealing with Norway rats, which are common in Toronto's older neighborhoods near ravines and the waterfront.
Step 2: Don't Open the Walls Yet
Most people think they need to tear open drywall to get rid of mice. In most cases, you don't. Mice enter and exit walls through small gaps — usually at floor level, around pipes, or near the foundation. Sealing those entry points and setting traps in the right locations is more effective (and way cheaper) than opening walls.
We only open walls in two situations:
- A dead mouse is decomposing inside and the smell is unbearable (rare, but it happens)
- There's visible structural damage to wiring or insulation that needs repair
Step 3: Set Traps in the Right Locations
Snap traps work. Glue traps are cruel and ineffective (mice can pull free, and you're left with a half-stuck, panicked mouse). Poison baits are risky — mice eat the bait, crawl back into your walls, and die somewhere you can't reach. Then you have a smell problem.
The best approach: snap traps baited with peanut butter, placed along walls where you've seen droppings or heard scratching. Check them daily. Mice are smart — if a trap sits for days without catching anything, they'll learn to avoid it.
Step 4: Seal Entry Points
This is the most important step. If you don't seal the holes mice are using to get in, trapping them is a losing battle. New mice will just keep coming in.
Common entry points in Toronto homes:
- Gaps around basement windows
- Cracks in the foundation (especially in older brick homes)
- Spaces around utility pipes, HVAC lines, and dryer vents
- Gaps where the siding meets the foundation
- Unsealed crawl space vents
We use steel wool, copper mesh, and caulk to seal these gaps. Mice can't chew through steel or copper. Foam alone doesn't work — they'll chew right through it.
Step 5: Clean Up Food Sources
Mice are in your house for three reasons: shelter, warmth, and food. Take away the food, and they're more likely to leave (or get caught in traps).
What attracts mice:
- Pet food left out overnight
- Crumbs and food debris under appliances
- Unsealed pantry items (cereal, rice, pasta)
- Garbage left uncovered
- Compost bins without tight lids
Store dry goods in airtight containers. Sweep up crumbs daily. Take out the garbage every night.
Step 6: Monitor for Activity
After trapping and sealing, you need to monitor. Set traps in key areas for 7-10 days after the last catch. If no new mice are caught and you hear no new scratching, the problem is likely resolved. If activity continues, there's either a gap you missed or a larger infestation that needs professional treatment.
When to Call a Professional
DIY works for small, early-stage infestations. But if any of the following apply, you need professional rodent control:
- You're catching multiple mice per day for more than a week
- You've sealed obvious entry points but mice keep coming back
- You're hearing scratching in multiple rooms
- You smell decomposition in the walls but can't locate the source
- You live in a condo or townhouse and suspect the infestation is shared across units
In Toronto's multi-unit buildings, mouse problems are rarely isolated to one unit. If you're in a Brampton townhouse complex or a Mississauga condo building and you've got mice, your neighbors probably do too. That requires coordinated treatment — sealing shared entry points, treating common areas, and monitoring across units.
We handle that kind of infestation regularly. We know where to look, how to seal entry points in older Toronto construction, and how to clear an infestation fast.
How Long Does It Take to Get Rid of Mice?
For a typical single-family home in Toronto with a small to moderate infestation: 7-14 days.
That includes:
- Initial inspection and treatment (traps set, entry points sealed)
- Follow-up visits to check traps and monitor activity
- Final sealing and cleanup
For larger infestations or multi-unit buildings: 3-4 weeks.
The timeline depends on how many mice you have, how many entry points need sealing, and whether there are ongoing sources of re-infestation (like shared walls in condos or gaps in communal areas).
What Happens If You Ignore It
Mice breed fast. A single female mouse can have 5-10 litters per year, with 5-6 babies per litter. That means a small problem in October can become a severe infestation by January.
The longer you wait, the worse it gets:
- More droppings = more health risk (mice carry Hantavirus, Salmonella, and other pathogens)
- More gnawing = more damage to wiring, insulation, and structural materials
- More nesting = harder to eliminate the population
And here's the thing nobody tells you: mice don't just stay in your walls. Once they're comfortable, they'll move into your kitchen, your bedroom, your kids' rooms. We've pulled nests out of couches, dressers, and the backs of ovens. It gets bad fast.
The Toronto-Specific Problem
Toronto's ravine system — one of the largest urban ravine networks in the world — creates natural mouse corridors. Homes backing onto ravines in neighborhoods like the Beaches, Don Mills, and Etobicoke see higher rodent activity, especially in fall when food sources in the ravines dry up.
Older homes near these ravines have two strikes against them: aging construction with easy entry points, and proximity to large outdoor mouse populations. If you're in one of these areas, you're dealing with a constant pressure problem. Sealing entry points is critical, and annual inspections are a good idea.
Get Help Fast
If you're hearing mice in your walls, don't wait. The problem won't fix itself, and it will get worse.
We offer same-day rodent control service across Toronto, Brampton, Mississauga, Vaughan, and the rest of the GTA. We'll inspect, trap, seal, and get rid of the mice — usually within two weeks.
You don't have to live with scratching in the walls. Call us, and we'll handle it.
Serving: Toronto, Brampton, Mississauga, Vaughan, Scarborough, and the Greater Toronto Area.