Mice Are Coming: How to Keep Them Out of Your Ontario Home Before Fall

Key Takeaway: Mice can enter through openings as small as 1/4 inch, so preparing your home before fall is one of the best ways to reduce the chance of a mouse infestation. Inspect your home's exterior, seal potential entry points, remove food sources and watch for early signs of activity.

Mice season is coming. As summer starts to wind down and temperatures gradually become cooler, Ontario homeowners should start checking their homes for the small gaps and openings mice can use to get inside.

You may not see a mouse yet, but that doesn't mean one isn't looking for a way in.

Mice are excellent at finding warm, sheltered spaces with easy access to food. A mouse can squeeze through an opening as small as 6 mm (about 1/4 inch), making seemingly minor gaps around doors, pipes, vents and foundations potential entry points.

For homeowners across Brampton, Mississauga, Oakville, Milton, Hamilton and other parts of Southern Ontario, late summer is a good time to prepare before mouse activity becomes a problem.

Why Do Mice Come Inside Homes in the Fall?

Mice don't necessarily wait until winter to enter a home.

As outdoor temperatures begin to drop, mice start looking for places that provide warmth, shelter, food and water. Your house can provide all four.

Once mice find an opening into a home, they may move into areas such as:

• Basements

• Garages

• Wall voids

• Attics

• Crawl spaces

• Kitchens

• Storage areas

A home doesn't have to be old or poorly maintained to have a mouse problem. Even newer homes can develop small gaps around utility lines, doors, vents, siding and other areas.

That's why mouse prevention before fall is often easier than dealing with an infestation after mice have already established themselves inside.

How Small of a Hole Can a Mouse Fit Through?

This is one of the biggest reasons mice can be difficult to keep out.

A mouse can enter through an opening of approximately 1/4 inch (6 mm). Ontario government guidance recommends inspecting buildings regularly for possible rodent entry points and notes that cracks around doors, utility connections, vents and other openings can provide access.

If you can see a small gap around the exterior of your home, don't automatically assume it's too small for a mouse.

Common Mouse Entry Points to Check

Before fall arrives, inspect:

• Gaps around garage doors

• Spaces underneath exterior doors

• Cracks around the foundation

• Openings around plumbing and utility lines

• Dryer and bathroom vents

• Gaps around windows

• Areas where siding meets the foundation

• Roof and soffit openings

• Damaged screens or vent covers

• Openings around pipes and cables

Pay particular attention to areas where different building materials meet.

7 Ways to Keep Mice Out of Your Ontario Home Before Fall

1. Inspect the Outside of Your Home

Walk around your property and look carefully at the foundation, exterior walls, doors, windows, roofline and garage.

Look for:

• Cracks

• Holes

• Gaps

• Damaged screens

• Loose siding

• Spaces around pipes

• Gaps underneath doors

You don't need to find a large hole. Remember, mice can use very small openings to get inside.

2. Seal Potential Entry Points

Once you identify openings, seal them using appropriate materials that rodents cannot easily chew through.

Ontario guidance recommends materials such as coarse steel wool, hardware cloth or sheet metal for filling or covering rodent entry points.

Pay particular attention to areas around:

• Pipes

• Utility lines

• Vents

• Doors

• Foundation cracks

• Garage entrances

Simply covering a hole with a material that mice can chew through may not solve the problem.

3. Check Your Garage

Garages are an easy access point for mice.

Check the seal around your garage door and make sure it closes properly. Look for daylight underneath or along the sides of the door.

Also avoid leaving the garage door open for extended periods, particularly overnight.

Boxes, stored materials and clutter can also create sheltered areas where mice can hide.

4. Remove Food Sources

Mice don't need a large food supply to survive.

Keep food in sealed containers and clean up crumbs and spills quickly. Don't leave pet food sitting out overnight, and keep garbage and compost properly secured.

Outdoor food sources matter too.

Bird feeders, spilled bird seed, fallen fruit and unsecured garbage can attract rodents to your property. The City of Mississauga specifically warns that spilled bird seed can attract rats and mice.

Ontario also recommends securing garbage, cleaning up spilled food and removing fallen fruit and other potential food sources when trying to reduce small-animal activity around homes.

5. Keep Your Yard Clean

Your yard can provide mice with food and shelter before they ever enter your home.

Before fall, consider:

• Removing piles of leaves and debris

• Keeping firewood elevated and away from the house

• Cleaning up fallen fruit

• Trimming vegetation close to the home

• Removing unnecessary clutter

• Keeping garbage containers securely closed

Reducing food and shelter around the property can make your home less attractive to rodents.

6. Inspect Your Basement and Attic

Basements and attics can provide mice with quiet, protected spaces.

Look for signs such as:

• Small dark droppings

• Gnaw marks

• Shredded paper or insulation

• Nesting material

• Scratching sounds

• Unusual odours

• Food packaging with small chew marks

If you find evidence of mice, don't assume that removing the visible signs means the problem is gone.

There may be additional mice or an entry point that still needs to be addressed.

7. Don't Wait Until You See a Mouse

One of the biggest mistakes homeowners make is waiting until they see mice regularly before taking action.

A single mouse sighting can be a reason to inspect the property, especially if you also notice droppings, scratching sounds or signs of chewing.

If mice have already entered your home, simply setting out a trap may not address how they are getting inside.

A proper mouse control approach should identify the source of the activity, locate potential entry points and determine how extensive the problem is.

For more ways to protect your home from seasonal pests, see our guide to Preventing Common Household Pests in Ontario.

What Are the Signs of Mice in Your Home?

You may not always see a mouse.

Mice are often more active at night, so homeowners may notice evidence of activity before seeing the animal itself.

Common signs include:

Mouse Droppings

Mouse droppings are typically small, dark and rice-shaped. Ontario guidance notes that mouse droppings are generally rice-sized, while rat droppings are larger and bean-sized.

Scratching Sounds

Hearing scratching or movement inside walls, ceilings or other enclosed spaces can indicate rodent activity.

Chewed Materials

Mice can gnaw on food packaging and other materials while searching for food or creating nesting areas.

Nesting Material

Mice may use paper, fabric, insulation and other soft materials to create nests.

Unusual Odours

A persistent musty or unpleasant odour in an enclosed area can sometimes accompany rodent activity.

If you're unsure whether you're dealing with mice or rats, read our guide:

Mice vs Rats: How to Tell the Difference in Your Ontario Home

Do Newer Ontario Homes Get Mice?

Yes.

A newer home can still develop openings that mice can use to enter.

Construction gaps, utility penetrations, garage doors, vents and other exterior openings can provide potential access if they aren't properly sealed or if materials deteriorate over time.

The age of your home isn't the only factor.

Mice are opportunistic. If a property provides food, shelter and an accessible entry point, it can become attractive regardless of when the home was built.

When Should You Call a Professional for Mouse Control?

If you have noticed repeated mouse activity, droppings, scratching sounds or signs of nesting, professional mouse control may be appropriate.

Professional pest control can help determine:

• Where mice are entering

• Where they are nesting

• How extensive the activity may be

• What conditions are attracting them

• Which areas need to be sealed or addressed

• What treatment or monitoring approach is appropriate

Trying to address a mouse problem without identifying the source can sometimes result in temporary improvement followed by another occurrence.

Frequently Asked Questions About Mice in Ontario

When do mice start entering homes in Ontario?

Mice can enter homes at any time of year, but homeowners often become more concerned about mouse activity as temperatures begin to cool. Late summer is a good time to inspect your home and seal potential entry points before fall.

How small of a hole can a mouse fit through?

A mouse can squeeze through an opening as small as 6 mm (about 1/4 inch). Small gaps around doors, foundations, vents, pipes and utility lines can provide potential entry points.

How can I keep mice out of my house before fall?

Start by inspecting the exterior of your home for cracks and gaps. Seal potential entry points, repair damaged door and vent seals, keep food in sealed containers, secure garbage and remove clutter or other sheltered areas around the property.

What are the first signs of mice in a home?

Common signs include small dark droppings, scratching sounds, gnaw marks, nesting material and signs of chewing around food packaging. You may notice these signs before you actually see a mouse.

Can mice get into newer homes?

Yes. Newer homes can still have small openings around doors, vents, pipes, utility connections and other areas that mice may use to enter. The age of a home does not necessarily prevent mouse activity.

Should I be worried if I only saw one mouse?

One mouse sighting is a good reason to inspect your home for additional signs and possible entry points. Mice can be difficult to notice, so finding droppings, nesting material or repeated signs of activity may indicate that more investigation is needed.

How do I know if I have mice or rats?

Mice and rats have different sizes, droppings and behaviours. If you're unsure which rodent you're dealing with, read our guide Mice vs Rats: How to Tell the Difference in Your Ontario Home.

Get Your Home Ready for Mouse Season

You don't have to wait for temperatures to drop before preparing your home.

Late summer is a good time to inspect your property, seal potential entry points, secure food sources and look for early signs of rodent activity.

A few small gaps can be enough for mice to get inside, so prevention starts with the exterior of your home.

If you've already noticed mice or signs of rodent activity, First Choice Pest Control Inc. can inspect the property and help determine the best approach for your situation.

Don't wait until mouse activity becomes a bigger problem.

Contact First Choice Pest Control Inc. for professional mouse control in Ontario.