Mice or rats — how to tell
The species matters, because a mouse-sized gap and a rat-sized gap aren't the same repair, and the fix that stops one won't stop the other.
Mice
- Size / weight
- 12 to 25 grams
- Entry gap
- About 6 to 7 mm — roughly a dime standing on edge
- Droppings
- Small, 3 to 6 mm, rod-shaped with pointed ends
- Signs to look for
- Baseboards, behind the stove or fridge, kitchen drawers, back of lower cabinets. Faint ammonia smell in closed cabinets from urine trails. Shredded paper, insulation, or fabric nesting material.
Rats
- Size / weight
- Norway rat — the species in the GTA, including Whitby
- Entry gap
- About the diameter of a quarter, bigger than a mouse gap but still easy to miss
- Droppings
- Larger, around 20 mm, capsule-shaped with blunt ends
- Signs to look for
- Dark, oily smear marks (runways) along baseboards and wall junctions at floor level. Burrows at grade under slabs, compost bins, and foundations. Gnaw marks through wood, plastic pipe, and over time soft metal or concrete block.
If you see a mouse in daylight, that usually means the population has grown large enough that some animals have been pushed out of the preferred hiding spots. If what's chewing through your garage drywall or deck lattice seems too aggressive to be a mouse, it probably is.
Why fall is the season that matters in Durham
Mouse activity in the GTA — Whitby included — climbs from late September into November, as outdoor temperatures drop and mice look for a warm place to spend the winter. A mouse you notice in October has usually already been coming through the same gap for weeks; the sighting is rarely the beginning of the problem. Rats follow a similar late-autumn pattern, moving in from yard and garden burrows as the ground cools, with a second smaller push in early spring when outdoor food sources start up again.
Whitby's geography adds pressure on top of the calendar. The Lake Ontario shoreline, the Lynde Shores conservation lands, and the Lynde, Pringle, and Corbett creek valleys cut green corridors straight into residential streets, and established subdivisions like Williamsburg and Rolling Acres have the mature landscaping, older sheds, and settled grade that give rats cover and travel routes close to houses. The older housing stock around downtown Whitby and Brooklin carries its own risk — heritage and early-1900s homes tend to have more gaps around old chimneys, uncapped vents, and settled foundations, which gives mice, rats, and squirrels easier entry than a newer build.
One mouse is almost never one mouse. A female produces 5 to 10 litters a year, 3 to 12 young per litter — a small founding population can turn into dozens within a few months in a warm house with food available. Rats breed even faster: 5 to 6 litters a year, up to 12 young each, sexually mature in 3 to 4 months. Waiting to see if "it's just the one" almost always means dealing with a bigger job in December than you would have in September.
What a treatment visit covers
Inspection first
We trace droppings, grease marks, and gnaw evidence to find where mice or rats are active inside, then work backward to the entry points — plumbing and wiring penetrations, foundation cracks, poorly fitted doors, gaps in an attached garage wall. For rats, we also look for burrow sites and runways outside, since bait placement and exclusion depend on knowing where the animals actually travel.
Trapping or baiting
For mice, snap traps set along confirmed runways and near nesting sites bring an active population down, checked and reset on follow-up visits. For rats, we address the outside population and the interior entry points at the same time — sealing without dealing with an existing population traps animals inside, and eliminating the population without sealing lets the next wave back in.
Sealing the entry points
Every identified gap — pipe penetrations, wiring gaps, foundation cracks, garage and door threshold gaps — gets sealed with steel wool backed by proper fill, hardware cloth, or metal flashing depending on the location. For mice the standard is unforgiving: a 6 to 7 mm gap is enough, so this step is not optional.
Confirming it worked
We check trap and bait activity across follow-up visits until things go cold — no captures for several consecutive days — before calling the interior population resolved.
Prevention, going into winter
- Seal obvious gaps around utility penetrations, garage door seals, and foundation cracks before the fall push starts, not after you've already heard something in the wall.
- Keep firewood, mulch, and dense shrubs pulled back a foot or two from the foundation — that gap removes cover rats use to approach the house unseen.
- Store pet food, birdseed, and garbage in sealed containers rather than bags; both mice and rats are drawn in by an easy food source before they ever look for shelter.
- If you've had mice or rats more than one winter in the same house, the entry point almost certainly was never fully sealed the first time — trapping alone without sealing turns into an annual repeat rather than a fix.
Whitby service
We work out of East York and run scheduled Durham Region routes into Whitby — Brooklin, Port Whitby, Williamsburg, Pringle Creek, Rolling Acres, and downtown Whitby included. Whitby is about a 45 to 55 minute drive from our base, so it's normally booked as a scheduled appointment rather than a same-hour call. Wildlife and rodent jobs start at $395, with the final price depending on the number of entry points and the sealing work needed — you get that number after the inspection, not before.
See our full Whitby pest control coverage, or the mouse control and rat control service pages for the full treatment scope.