Scratching Noises in Your Walls: Mouse, Rat or Squirrel?

It is 1 a.m., the house is quiet, and something is scratching inside the wall behind the headboard. Or it is 7 a.m., the coffee is brewing, and something is running across the kitchen ceiling. In October, on the South Shore and in Montreal, noises in the walls mean mice far more often than anything else. But not always. Rats, squirrels, birds and bats all make noise inside a house, and each one calls for a different fix.

Every animal has a signature: the hour it moves, the weight of the sound, the part of the house it comes from. This guide shows you how to tell them apart by ear, how to confirm with the clues you find the next morning, which ones are urgent, and what to do (and not do) tonight.

How do you tell if the noises in the walls are mice, rats or squirrels?

Three questions settle most cases. What time do you hear it? Is it light or heavy? Is it scratching, chewing, running or flapping?

Mice: light scratching and scurrying, strictly after dark

A house mouse weighs 15 to 25 grams, and it sounds like it. You hear a short, dry scratch, like a fingernail on cardboard, then a burst of tiny quick footsteps that stop dead. A mouse chewing wood or drywall makes a faint rasping, like a pencil dragged across a ruler, in bursts of a few seconds.

Timing is your best clue. Mice come out at dusk and go back to the nest at dawn, with two peaks: the hour after the lights go off and the hour before sunrise. If you hear it at 11 p.m. and again at 5 a.m., but never at 2 in the afternoon, think mouse.

Rats: heavy gnawing, thumps and slower movement

The Norway rat, the species found in Montreal and on the South Shore, weighs 250 to 500 grams, ten to twenty times a mouse. You can hear the difference. Instead of scurrying, you get distinct, slower footsteps and the occasional thump when the animal drops off a joist. The gnawing is deeper and more persistent, and a rat working on a beam or an ABS drain pipe does not sound anything like a mouse.

Rats are nocturnal too, but they stay low. The sound comes from the basement, the crawl space, under the ground floor or behind the washer. In Montreal plexes, rats come up from the back alleys and old sewer connections, and the noise almost always starts in the basement or the rear wall of the ground floor.

Squirrels: running, rolling and daytime noise in the attic

Grey squirrels work the day shift. They leave the nest at sunrise, head out again in the late afternoon and settle in before dark. If the noise above the ceiling starts at 6:30 a.m., starts again around 4 p.m., and the night is silent, you almost certainly have a squirrel and not a mouse.

The sound is different too. A squirrel runs, it does not scurry. You hear a fast gallop from one end of the attic to the other. It rolls nuts, acorns and chunks of insulation, which sounds like a marble on the floor above your head. In the fall it stockpiles food and builds a winter nest, and a litter is born in late winter, which is why calls peak from October to November and again from February to March. Heavy running in the attic at night, on the other hand, is more likely a raccoon.

Birds and bats: flapping, fluttering and chirping

A bird stuck in a dryer duct, a bathroom vent or a hollow wall produces a panicked flapping, mostly in the morning, often with chirping. Starlings and sparrows nest in the spring in vents without screens and behind soffits that have pulled away from the house.

A bat colony in the attic produces dry scratching and faint high-pitched squeaks at sunset, when the bats leave, and at dawn, when they return. The surest clue is not the sound but the guano: small black pellets piled below the exit point, often on a windowsill or a balcony.

Where is the noise coming from: the walls, the attic or the basement?

The location tells you nearly as much as the sound.

In the walls. The walls belong to mice. They travel up and down the cavities along pipes and wires and come into rooms through the gaps around plumbing, under the sink and behind the stove. A squirrel sometimes drops into a wall cavity from the attic and cannot climb back out. The noise is then frantic, constant and always in the same spot, and you need to act fast.

In the attic. Daytime means squirrel. Night with a light sound means mouse, which climbs brick and downspouts with no trouble. Night with a heavy sound means raccoon. In Montreal's flat-roofed plexes the attic is shallow, sometimes under 60 cm, and the noise seems to come from everywhere at once. In the 1950s and 1960s bungalows of Greenfield Park, Saint-Hubert and old Brossard, wooden soffits and unscreened roof vents are the classic squirrel entrance, and the joint between the roof and the wall is the classic mouse entrance.

In the basement. The basement and crawl space are rat territory, especially near the floor drain and the walls facing the alley or the compost bin. A noise in the basement wall at sill-plate level (the wood resting on the foundation) often marks the exact spot where the animal gets in.

If you rent, the noise may be coming from the unit next door. Mice move between apartments through plumbing chases and shared walls. Notify the landlord in writing, because in most cases it is their responsibility to have the building treated.

Which clues should you combine with the sound to confirm the animal?

The sound gives you a theory. The morning clues confirm it.

• Droppings. This is the deciding clue. Mouse: black rice grains, 3 to 6 mm, pointed at both ends, by the dozen. Rat: blunt capsules, 12 to 20 mm, fewer of them. Squirrel: cylindrical pellets of 8 to 12 mm, often piled in one spot in the attic. Our guide to the 10 signs of mice in your house explains how to tell fresh droppings from old ones.
• Grease marks. A grey or brown smear along a baseboard, a pipe or a joist is the repeated passage of a rodent with oily fur. Thin and at floor level: mouse. Wider, darker and 5 to 10 cm off the floor: rat.
• Entry holes. A mouse fits through 6 mm, the width of a pencil. A clean hole of 2 cm or less with fine tooth marks is a mouse. A rat leaves holes of 5 cm and up with wood chips around them. A squirrel chews a 7 to 10 cm hole through a soffit, fascia or roof vent and shreds the wood around it. Our guide on how mice get into your house walks through every weak point from the foundation to the roofline.
• Nesting material. Mouse: a loose ball of insulation, paper and fabric about 10 to 15 cm across, tucked into a closed corner. Squirrel: a ball-sized heap of leaves, twigs and torn insulation in the attic. Bird: twigs and dry grass packed into a vent or duct.
• Smell. Ammonia in a cabinet or a closed corner: mice or rats that have been established for weeks. A strong musky smell in the attic: squirrel or raccoon. A rotten smell: a dead animal in the wall, often after a do-it-yourself poisoning.

Hearing noise at night and just found droppings in the cabinet? Extermination BETA is based in Brossard and offers same-day response in Longueuil, Saint-Hubert, Saint-Lambert, Greenfield Park, La Prairie, Chambly, Montreal and across Greater Montreal. The first inspection is free. Call 438-253-3000 or use the contact page, and describe the noise, the time of day and what you found.

Which animal is the most urgent, and why?

No noise in the walls fixes itself, but the urgency depends on the animal.

Mice: urgent because of speed. A female has a litter every month from about six weeks of age. A faint scratch in October is a full family by December. Mice chew wire insulation too, but they do far less structural damage than the next two.

Rats: urgent because of damage. A rat gnaws framing lumber, ABS drain pipes, electrical wiring and even crumbling mortar. Bare wires behind a wall are a genuine fire risk, and a rat in the house is an animal that travels between your cabinets and a sewer.

Squirrels: urgent because of wiring and insulation. A squirrel chews wires the way it chews branches, and it tears out insulation to build its nest. It enlarges its entry hole every time it passes through. It is also wildlife, not a structural rodent like a mouse. In most cases you do not poison it: rodenticides sold for mice and rats are not registered for squirrels, so using them that way is not legal, and a dead squirrel in the attic smells for weeks. The job is done by exclusion instead: a one-way door is fitted over the entry hole, the animal leaves to feed and cannot get back in, then the hole is sealed. In Quebec, capturing and relocating wildlife is governed by its own rules, and this kind of work is often handled by a wildlife specialist. If you suspect a squirrel or a raccoon, call and describe the situation. We will tell you straight whether it is a job for us or for a wildlife specialist.

Bats: exclude, never kill. Several bat species are in decline in Quebec. In most cases the only accepted approach is exclusion, done outside the period when the pups cannot fly yet (roughly June to mid-August). No poison, and never seal the opening with the colony inside.

What should you do tonight when you hear noises in the walls?

You do not have to solve it tonight, but you should start gathering information and remove the food.

1. Log the time and the type of noise. After three or four nights the pattern is clear: nocturnal and light, mouse; nocturnal and heavy, rat or raccoon; daytime, squirrel or bird. That log saves the technician time.
2. Pin down the location. Put your ear to the wall, move along it, and mark the spot with painter's tape. A noise that is always in the same place, especially a frantic one, may mean a trapped animal.
3. Lock up the food. Cereal, flour, rice, pasta, nuts and pet food go into hard containers with lids. Take the bag of kibble out of the garage. With no easy food, mice and rats turn to the traps.
4. Run the flour test. A thin layer of flour or cornstarch along 30 cm of the suspect wall. In the morning the tracks tell you the size of the animal: a few millimetres with a tail drag, mouse; paw prints around 2 cm, rat.
5. Set two or three snap traps for mice along the baseboards, trigger end to the wall, with peanut butter. Traps that are sprung but empty, or bait that vanishes with no catch, mean something bigger than a mouse.
6. Look at the roof tomorrow. A hole in the soffit, an open roof vent, insulation hanging out: that is a squirrel's signature.

What should you not do?

The most common mistakes are also the most expensive ones.

• Do not put poison in the walls or the attic. This is mistake number one. A poisoned animal dies where it hides, in a wall cavity or under the insulation, and the smell of decomposition lasts two to four weeks. For a squirrel or a bat it is also, in most cases, against the rules. A professional uses locked, anchored bait stations placed where the rodents can be recovered.
• Do not seal the hole with the animal inside. Closing the entry tonight locks the family in with you. Mice and rats chew a new route, often into a living space. A squirrel shut in will shred whatever it can to get out, and a mother cut off from her young can tear through a soffit to reach them. Get them out first, seal after.
• Do not bang on the walls to scare it off. It works for ten minutes and moves the problem to another cavity. The same goes for ultrasonic repellers and mothballs: no lasting effect.

When should you call an exterminator?

Call if any of these apply to you.

• The noise has gone on for more than a week, or you hear it on more than one floor.
• The traps catch a mouse a night for several days, which means the nest is producing faster than you are catching.
• The sound is heavy, or you have found droppings longer than 10 mm.
• The noise comes from the attic during the day: there is exclusion work to do and wiring to check.
• There is a rotten smell: the animal has to be located and removed.

What a professional brings first is identification. In one visit, a technician who hears your description, looks at the droppings and walks the foundation and the roofline knows whether it is a mouse, a rat or wildlife, and places the equipment where the animals actually travel. Extermination BETA's rodent control service follows that sequence for mice and rats: inspection, species identification, locked bait stations and traps out of reach of children and pets, follow-up, and a list of what to seal. The technicians are certified and hold the Quebec CD pesticide permit.

On cost, in Quebec you generally pay 250 $ to 700 $ for a basic mouse treatment, including the inspection, the equipment and a follow-up visit. For rats, expect more like 300 $ to 900 $. Sealing entry points is billed on top, often 200 $ to 1,000 $ depending on the number of openings. Squirrel exclusion by a wildlife control company generally runs from 300 $ to well over 1,000 $ depending on roof height and the repairs needed. A plex in Montreal does not cost the same as a bungalow in Chambly, so call for an exact quote.

Frequently asked questions

Do mice make noise during the day?

Rarely. A mouse active in daylight in an occupied house usually means the population is large or the nest was just disturbed. If the noise is regular at 7 a.m. and 4 p.m. and the night is quiet, it is a squirrel or a bird, not a mouse.

What is a noise in a single wall, always in the same spot?

Two possibilities. Either it is the entry point or the nest, and the animal comes back to it every night. Or it is a trapped animal, especially if the noise is continuous, frantic and goes on for hours. A squirrel or a bird that falls into a wall cavity cannot climb back up. In that case call quickly: a small opening can be cut at the bottom of the wall to let it out alive.

How long does a dead animal in a wall smell?

For a mouse, one to three weeks depending on temperature and airflow. For a rat or a squirrel, often three to five weeks, and the smell is much stronger. Air fresheners mask it without fixing it. The animal has to be located, removed, and the spot disinfected.

The noise stopped a few days ago. Is it over?

Probably not. Mice change routes when you move things around or set traps, and two or three quiet days in October usually mean the animal found a better corner of the same house. Keep the flour test going for another week before you conclude anything.

Hearing scratching in the walls? Find the animal before it settles in

Noises in the walls in October do not wait for spring. A mouse becomes a family, a rat widens its passage, a squirrel tears out insulation and chews wiring. Log the times tonight, put down the flour and a couple of traps, and look at the roof tomorrow morning. If you are not sure what you have, we will sort it out.

Extermination BETA serves Brossard, Longueuil, Saint-Hubert, Saint-Lambert, Greenfield Park, La Prairie, Chambly, Montreal and Greater Montreal, with same-day response and a real 24/7 emergency line. Call 438-253-3000 or reach us through the contact page. The first inspection is free, you get 15 percent off your first service, and if it turns out to be a squirrel or a bat, we will tell you straight and point you in the right direction.