Signs of Rats in Your House: What Ontario Inspectors Actually Look For

Quick answer: The reliable signs of rats are droppings 12–18 mm long and capsule-shaped (mouse droppings are 3–6 mm and pointed), gnaw marks with tooth grooves 3–4 mm wide, dark greasy smear marks along baseboards and joists where rats run the same route nightly, heavy dragging sounds rather than light scratching, and — the check almost no homeowner does — burrow holes 50–100 mm across in soil along the foundation, under decks, beside garages and behind sheds. Mice exploit gaps; rats make openings. Rat-sized droppings or burrows mean the entry point is structural and has to be found and sealed, not just trapped. Call Sani IQ at (705) 302-1887.

Why You’re Noticing This in October

Rat activity inside Ontario homes is strongly seasonal, and the trigger is the first run of cold nights. Through the summer, Norway rats — the species behind almost all Ontario house infestations — live outdoors perfectly well: burrows in soft soil along foundations, under decks and sheds, in compost, beside garbage storage, along overgrown ravine edges. They do not need your basement. Once overnight temperatures drop and the outdoor food supply thins, those colonies start probing the building for warm, dry harborage with food access. That is why the evidence appears suddenly: the colony did not grow overnight, it moved.

The second factor is construction. Digging, sewer work, demolition and new builds displace established colonies, and the animals relocate into older adjacent neighbourhoods — a legitimate explanation for a problem that was not there last year. We see the pattern consistently in the older housing stock of Etobicoke, where mature trees, aging sewer laterals and decades-old foundations give rats both routes and cover.

Rat Evidence vs. Mouse Evidence

Most homeowners who think they have rats have mice, and a smaller number who think they have mice have rats. The distinction matters because the two problems have different solutions.

Droppings — the most dependable single indicator. Norway rat droppings are 12–18 mm long, thick and blunt-ended, roughly the size of a large grain of brown rice. Mouse droppings are 3–6 mm, thin and pointed at both ends. There is no overlap. Rats deposit in concentrated latrine areas; mice scatter droppings along every route they travel.

Gnaw marks. Rat incisors leave paired grooves 3–4 mm wide with visible chisel marks, and rats gnaw through materials mice cannot manage: wood framing, soft mortar, aluminum flashing, plastic drain pipe. Mouse gnawing is fine, shallow and confined to soft materials and existing edges.

Smear marks — specific to rats, and most homeowners have never heard of them. Rats run the same route nightly keeping body contact with a wall, and over weeks oil and dirt from their fur build into a dark greasy band along baseboards, joists and pipe runs. A flashlight at a low angle reveals it. Mice leave faint dust-and-urine trails instead.

Sound. Mice sound like light scratching high in a wall cavity. Rats sound heavier — thumping, dragging, gnawing audible from another room. People call rat noise alarming and mouse noise annoying, and the instinct is usually right.

Our rodent library section covers the common Ontario rodents side by side.

The Exterior Check Homeowners Never Do

Nearly every homeowner inspects the kitchen, the basement and under the sink. Almost nobody walks the perimeter looking down — and that is where a rat problem is diagnosed. Do this with a flashlight, slowly, all the way around the house:

Burrow holes. Norway rats dig. An active burrow entrance is 50–100 mm across — golf ball to tennis ball — roughly circular, with the soil at the mouth smooth and compacted from traffic, and clear of leaves and cobwebs. Look along the foundation wall, under decks and porches, at the base of garage slabs and sheds, beside compost and garbage storage, under dense ground cover and along fence lines.

The soil line and every penetration in it. Gaps, settlement cracks and eroded channels where the ground meets the foundation; gas lines, hose bibs, electrical conduit, AC line sets, dryer vents and floor drains; broken crawlspace vent screens, unprotected brick weep holes, missing vent dampers. A gap a rat can get its head into is a gap it can widen.

Garage doors. The corner gap where the weather seal curls up at the bottom of the frame is one of the most common rat entries in Ontario suburbs, and easy to miss — it only shows with the door closed and a light outside. We find it constantly in Innisfil and across Simcoe County, where detached garages back onto fields and ravine corridors.

Roof and tree lines. Norway rats climb better than people expect: overhanging branches, downspouts and vines give access to soffit gaps, roof-vent boots and the chimney chase.

Why Rats Are a Structural Story and Mice Are a Gap Story

A mouse needs about 6 mm — a pencil’s width. Mouse control is largely about sealing a long list of small existing openings: utility gaps, weep holes, poorly fitted trim, pipe chases. The building does not need to be wrong for mice to get in; it just needs to be a building.

A rat needs about 20 mm, which most houses do not offer by accident — so rats create their entry. They gnaw a gap wider, dig under a footing, enlarge a rotted sill, exploit a broken sewer lateral or an unsealed floor drain. A rat entry point is therefore often a sign of a building defect: failed mortar, rotted wood at grade, settlement, a damaged vent, a breached drain line. Fixing the rodent problem and fixing the building problem are the same job.

It also means trapping alone almost never ends a rat infestation. Remove the animals inside and the colony outside sends more through the same opening within days. Exclusion is the control measure; trapping is cleanup.

That is why we treat rat work differently from mouse work. Our rodent programs in Scarborough and Etobicoke — where older housing stock and mature infrastructure generate the heaviest rodent pressure — start with entry forensics and burrow mapping, not bait placement.

What a Professional Inspection Actually Produces

A rat inspection done properly is an evidence exercise, not a sales call. Expect:

• Burrow mapping. Every active burrow located, counted and marked — which is also how we estimate colony size. Two active burrows and a dozen are very different problems.
• Entry forensics. Tracing the route from exterior evidence to interior: which opening, which void, which path through the structure. Dust, smear marks, dropping density and gnaw freshness read like a trail.
• Freshness assessment. Old droppings are grey and crumble; fresh ones are dark and shiny. That separates an active infestation from historical evidence — which matters if you are buying a house.
• A written exclusion list: which openings to close, in what material, in what priority order.
• Monitoring plan. Tamper-resistant stations placed per Ontario label requirements and documented, with pet and child safety addressed explicitly.

Our technicians are employed by Sani IQ, licensed and background-checked — never subcontracted. Sani IQ is BBB Accredited, carries $5 million in liability coverage, is licensed under the Ontario Pesticides Act and registered with the Ministry of the Environment, Conservation and Parks.

The Bylaw Side: Who Is Responsible

Municipal property-standards rules in Ontario put rodent control on the property owner, which surprises people. Toronto’s property standards rodent-control requirements oblige owners to keep premises free of rodents and eliminate harborage and food sources; Toronto Public Health covers the public-health side. Most GTA, York, Durham and Simcoe municipalities have equivalent provisions.

Practically: a homeowner owns the remediation, and an unaddressed complaint can become an order. For a landlord, a rodent-free unit is your obligation, not the tenant’s, and documented professional service is your evidence you met it. A tenant should report it in writing and keep the record — you are not expected to fund structural exclusion.

On health risk: rats spread pathogens through droppings, urine and contaminated food-contact surfaces, so cleanup needs gloves and ventilation, and dried droppings should never be swept or dry-vacuumed. The U.S. Centers for Disease Control’s rodent guidance is a sound non-commercial reference.

One-Time Treatment or Year-Round Protection?

With active rat evidence right now, a one-time service is the entry point — it stops the immediate problem, removes the animals inside, and gives you the exclusion list. But the colony that sent rats into your house lives outside it, and will still be there next October. In a neighbourhood with established pressure — older sewers, nearby construction, ravine corridors, lane-way garbage storage — a single treatment resets the clock rather than stopping it.

That is why Year-Round Protection is the path we recommend for rodents specifically. Seasonal inspections catch a new burrow while it is still a burrow and not a family in your soffit; exterior monitoring intercepts the autumn push before it becomes an interior problem; and the returning technician already knows your building’s weak points. Against one infestation’s real costs — gnawed wiring, contaminated insulation, destroyed stored goods, and repairing whatever opening they made — a year of protection is usually the cheaper side of the comparison.

Review the options on our plans and pricing page, or take the free quote quiz and we will tell you which level matches your property. Every service starts with a professional inspection, credited in full when you book the treatment. Call (705) 302-1887.

Frequently Asked Questions

What is the first sign of rats in a house? Usually droppings or sound. Capsule-shaped droppings 12–18 mm long are definitive. Heavy night-time movement overhead — dragging and thumping rather than light scratching — is the other common first signal.

Do I have rats or mice? Measure a dropping. 12–18 mm, blunt-ended: rats. 3–6 mm, pointed: mice. Then check for greasy smear marks along baseboards and joists, which rats leave and mice do not, and walk the exterior looking for 50–100 mm burrow holes.

Can you have rats and not see them? Does one rat mean an infestation? Not seeing them is the normal case — Norway rats are nocturnal and avoid people. A rat seen in daylight suggests a large population or a displaced animal. And one confirmed rat inside almost always means an established colony outside, because rats are social burrowing animals that rarely travel solo. Inspect the perimeter rather than treating it as isolated.

How did rats get in if my house is sealed? They very often made the opening. Rats gnaw through wood, soft mortar, plastic pipe and thin metal, and dig under footings, slabs and decks. Common routes: a gnawed garage-door corner seal, a damaged crawlspace vent, an unsealed floor drain or sewer lateral defect, gaps beside utility penetrations at grade.

How long does it take to get rid of rats? Weeks, not days. Removing the animals inside is quick; what determines whether they come back is exclusion plus exterior management of the burrow system.

Should I just use bait from the hardware store? It is the approach most likely to leave you with a dead rat inside a wall cavity and an unresolved entry point, and over-the-counter rodenticide carries genuine secondary-poisoning risk to pets and wildlife. Professional programs use tamper-resistant stations placed to Ontario label requirements and treat exclusion as the actual control.