Mouse or rat in the house: signs, prevention, solutions
Published on October 16, 2026
5 mins reading time
Mice and rats only need a small opening to get into a home. Once settled in, they can contaminate food, cause damage and reproduce quickly. Here’s how to identify their presence, keep them away and know when to call an exterminator.
Key takeaways
- Mice and rats can cause property damage and health problems.
- A mouse can squeeze through an opening as small as 6mm.
- Droppings, noises in the walls and gnawed packaging are among the first signs of an infestation, which can be limited by acting quickly.
How to tell if there are rodents in a house?
Signs of mice or rats are generally easy to spot: droppings, scratching noises, gnawed packaging, teeth marks, a urine odour or dead rodents.
How to tell whether it’s a rat or a mouse?
To tell a rat from a mouse, look mainly at their size, droppings and tracks. Noise can also offer a clue, but it can’t identify the species with certainty.
Mice often nest in walls, cupboards, ceilings or insulation. They generally move quickly and lightly.
Rats are heavier and can be noisier. They prefer basements, crawl spaces, the areas around foundations and drainage systems.
Comparison table: Mouse vs. Rat
Identification criteria | Mouse (Mus musculus) | Sewer rat or brown rat (Rattus norvegicus/rattus) |
|---|---|---|
Size (including tail) | 12 to 20cm | 30 to 45cm |
Appearence | Large ears, long tail, brown fur with a grey belly (house mouse) or brownish-grey fur with a white belly (deer mouse) | Stocky body |
Droppings (size of mouse or rat droppings) | Size of a grain of rice | Size of an olive pit |
Opening required | Can squeeze through a 6mm hole (the size of a pencil) | Needs an opening of 12mm or more |
Preferred habitat | Dry indoor spaces: walls, ceilings, cupboards | Basements, drains, foundations, burrows |
Common damage | Food packaging, electrical wires, insulation | PVC pipes, structure, foundations |
Why do rodents move into a house?
Mice and rats move into homes because they find food, water and shelter.
As cold weather approaches, they look for a warm place to take refuge. Since they don’t hibernate, they stay active all year.Accessible food sources, such as food, garbage and crumbs, can also attract them.
Are mice and rats pests?
In nature, mice and rats play a role. In a home, however, their presence can be a problem.
Beneficial
- Used in scientific research
- Kept as pets
- Food source for other species
Pests
- Contaminate buildings with their saliva, urine and droppings
- Contaminate food
- Gnaw on certain materials or items: wires, building materials, books, cardboard, plastic and woodwork
- Can transmit diseases (salmonellosis), bacteria and parasites
- Can bite or attack
How to keep mice and rats from getting in?
To keep rats and mice out, you first need to block the entry points into the home.
- Repair broken sewer pipes or add a backwater valve to the pipes connected to basement plumbing fixtures.
- Install metal door sweeps under doors and caulk around windows.
- Seal cracks in the foundation and other openings.
- Repair damaged pipes or drains.
- Store dry food in airtight containers.
- Clean up crumbs and food residue promptly.
How to keep rodents out of the yard?
- Mow tall grass along the edge of your property.
- Avoid letting clutter build up near the house.
- Use tightly closed outdoor garbage cans.
- Store firewood away from the foundation.
- Eliminate sources of standing water.
- On the first cold days of fall, keep doors firmly closed.
How to get rid of rats or mice?
Spring traps are generally the most effective way to get rid of rats or mice.
- Place traps along walls.
- Use scented bait, like peanut butter, bacon grease mixed with oatmeal, raisins or gumdrops.
- Check traps every day.
- Keep monitoring for several weeks. Reset traps 2 to 3 weeks after the last catches to trap rodents that have reached maturity.
Electric traps and live traps are also available.
Is it legal to use rat poison?
Yes. Since rats and mice are considered pests, it is permitted to exterminate them. You can use food poisoned with anticoagulant rodenticide, so that rodents die and dry out afterwards in their lair.
Warning: Rodenticides pose risks to children, pets and wildlife. They must always be used in accordance with the manufacturer’s instructions and applicable regulations.
When to call an exterminator?
Contact a professional exterminator when:
- Catches are increasing
- You see several rodents
- The rat or mouse infestation keeps coming back despite your efforts
- You suspect there are rats in the drains or under the slab
- You can’t find the entry points
How much does an exterminator cost?
The cost of a mouse or rat exterminator depends on several factors:
- Type of rodent
- Extent of the infestation
- Number of visits required
- Treatments used
- Size of the building
Tip: Get several quotes.
How to find a dead mouse in a wall?
A strong, persistent odour can indicate a dead rodent in a wall.
To find the source:
- Locate where the odour is strongest.
- Inspect areas where signs of activity have already been seen.
- Check attics, basements and crawl spaces when possible.
If the carcass remains inaccessible or if the odour persists, professional help may be needed.
Does home insurance cover rodent damage?
Generally, home insurance doesn’t cover damage caused by mice, rats and other vermin under basic policies.
Check your policy to confirm the exclusions and coverage that apply to your situation.
Frequently Asked Questions – Mice and rats
Mice are often found in walls, cupboards, ceilings or insulation. Rats prefer basements, crawl spaces, foundations and drainage systems.
Mouse droppings are the size of a grain of rice. Rat droppings are more the size of an olive pit.
Peppermint can bother mice, notably because of its strong smell, but it isn’t a reliable way to keep them away.
Yes, a mouse can squeeze through a 6mm hole, about the size of a pencil.
It can certainly live long enough to reproduce several times. A litter can have up to about ten young.
To learn more about mice and rats
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