Mice are good climbers. In Ontario they head indoors from September to November, and many reach the attic from outside by running up brick, siding or downspouts to the eaves, or up through the wall cavities from a basement entry point. Attic insulation is warm, quiet and easy to tunnel through, which is why an attic problem often feels impossible to finish: the mice are spread out under the insulation, away from the traps, and the way in is high up and hard to see.
Is it mice or squirrels in my attic?
Listen to when the noise happens. Mice are active at night, with light scratching and scurrying. Squirrels are active by day, loudest around sunrise and late afternoon, and sound heavier. Raccoons are much louder, usually at night, and leave torn shingles, vents or soffit panels you can see from the ground. The difference matters, because squirrels and raccoons are wildlife, not a pest-control job, and different rules apply.
| What you notice | Likely animal | Who handles it |
|---|---|---|
| Light scratching at night, droppings the size of a grain of rice, tunnels in the insulation | Mice | You, or a licensed exterminator |
| Heavier scratching at night, droppings 1 to 2 cm, gnawed wood | Rats | Licensed exterminator |
| Running and rolling sounds at dawn and dusk, chewed hole at a roof vent or fascia | Squirrels | Wildlife removal company (exclusion with a one-way door) |
| Loud thumping at night, torn soffit or vent, large droppings in one spot | Raccoons | Wildlife removal company |
| Chirping or scratching at dusk in summer, small dark droppings near a gable | Bats | Wildlife removal company; never handle bats |
Why are my traps not catching the mice in the attic?
Usually one of four things is going on. Each has a fix.
- The entry point is open. New mice keep arriving, so the catch never drops to zero. Sealing is the step that ends it.
- The traps are in the wrong place. Mice run along edges: the top plates of walls, along the rafters at the eaves, beside ductwork and along the attic hatch frame. A trap in the middle of open insulation is rarely crossed.
- There are too few traps. Health Canada suggests about one trap per metre along runways. In an attic that means a dozen or more along the edges, not two by the hatch.
- The mice are shy of new objects. Health Canada notes that leaving traps unset for three to four days before baiting them helps, and that used traps work better than new ones.
Bait with a pea-sized amount of something sticky, such as peanut butter, so the mouse has to work at the trigger. Snap traps and electronic traps are the most effective types. Check the traps every day; a dead mouse left in a hot attic smells within days.
How do mice get into the attic?
Mice need a gap about the size of a dime, according to Health Canada. Around the roofline, the usual openings are:
- Where the soffit meets the wall, or a soffit panel that has sagged or pulled out of its channel.
- Roof returns, the short sections where a lower roof meets a wall or another roof. The end caps there are often left open.
- Gable vents and roof vents without metal screening, and plastic vents a squirrel has already chewed open.
- The gap behind the eavestrough where the fascia board has rotted.
- Gaps around the plumbing stack, the chimney, cables and the air conditioner line set where they enter the house.
- Ivy or tree branches touching the roof, which give mice a ladder.
Look from the ground with binoculars on a sunny day, and from inside the attic with the lights off in daytime: daylight around the eaves shows you a gap. Seal with metal, not foam or caulk on its own. Health Canada recommends fine metal mesh over attic vents and soffits, and steel wool packed around pipes before caulking. Hardware cloth, metal flashing and copper mesh are what pros use at the roofline.
Should I seal the holes before or after trapping?
Seal the outside gaps first or at the same time as you start trapping, but not every opening at once if you suspect squirrels or raccoons, because you can trap an animal inside. For mice, sealing and trapping together is the standard approach: trapping alone lets new mice in, and sealing alone leaves the ones inside to move down into the walls and kitchen. Keep trapping until you have caught nothing for one to two weeks.
Do I need to replace attic insulation after mice?
Not always. A few droppings and short tunnels near the eaves can be cleaned in place. Replacement makes sense when droppings and urine are spread across a large area, when the insulation smells, or when it has been packed down so much that it no longer insulates. Removing contaminated insulation is a messy job done with a vacuum truck and protective equipment, and it is usually quoted separately from pest control.
When should I call an exterminator for mice in the attic?
Call a licensed exterminator if you are still catching mice after two to three weeks, if you hear activity in the walls as well as the attic, if you see signs of rats, or if you cannot reach the attic safely. In Ontario, applying pesticides as a paid service requires a structural exterminator licence from the Ministry of the Environment, Conservation and Parks. A good exterminator finds the entry points and tells you which ones to close, rather than only setting bait. If the noise points to squirrels or raccoons, call a wildlife removal company instead: Ontario requires live-captured wildlife to be released within 24 hours and within 1 kilometre of where it was caught, so exclusion, not relocation, is what solves it.
On Doyo, Rodent Control is $531, the full price with Doyo's fee included. It covers a licensed exterminator, entry points found and reported, traps and bait stations set, and one follow-up visit. Pest control pros on Doyo hold an Ontario Structural Exterminator licence, which Doyo checks before they are offered the work. Tell the Doyo agent the mice are in the attic, whether there is an attic hatch, and whether children or pets are in the home.