Signs of mice in your home: the 8 indicators that mean you have a problem

The eight reliable signs

Fresh droppings: dark brown, soft, shiny. 3-6 mm long, granular, pointed at one end. Multiple locations means active colony.
Chewed weatherproofing or soft plastic: especially around exterior doors, basement window frames, and utility penetrations. Mice chew to maintain incisor length and to widen entry points.
Greasy 'rub marks' on baseboards or behind appliances: rodent fur deposits oils along consistent runways. Look in narrow gaps where the wall meets the floor.
Gnawed food packaging: cardboard cereal boxes, soft plastic bags. Mice prefer these over rigid containers; they don't chew through glass or thick plastic.
Faint ammonia smell: concentrated rodent urine has a distinct sharp odour that becomes obvious in enclosed spaces (under-sink cabinets, pantry corners).
Sounds at night: scratching, scurrying, or running between 9pm and 3am. Often inside walls or in attic.
Pet behaviour changes: dog or cat fixating on a specific wall, floor area, or appliance repeatedly. Cats especially detect mice by scent before homeowners notice anything.
Visible mouse activity: actually seeing a mouse means the population is significant. Mice avoid daylight and human presence; sightings happen when their normal hiding capacity is exceeded.

How to tell active from past activity

Sweep the area where you found droppings. Mark the date with painter's tape. Check 48 hours later. New droppings means active. No new droppings over a week could mean past activity (previous tenant or seasonal incursion that resolved). Confirmation matters because it changes urgency — active means call within a week; past means inspect for entry points but no immediate treatment.

Frequently asked questions

How long until signs appear after mice get in?+

Droppings show up within hours of mouse activity in a new area. Greasy rub marks take 1-2 weeks of repeated use to become visible. Sounds at night are usually the latest sign — they only become noticeable when population reaches a level that disturbs sleep.

Can I distinguish mouse signs from rat signs?+

Yes — by size. Mouse droppings 3-6 mm; rat droppings 12-20 mm depending on species. Mouse rub marks are narrower and lower than rat rub marks. Mouse gnaw marks are smaller, fine-textured; rat gnaw marks are visibly toothy.

If I see a mouse during the day, does that mean it's bad?+

Daytime sightings indicate either a heavy infestation pushing into daylight foraging, or a single stressed individual. Either way, document and treat — daytime sightings are not normal mouse behaviour and shouldn't be dismissed.

Where to look in a Metro Vancouver home

Not every room is equally likely. Metro Vancouver homes concentrate mouse activity in three zones: the kitchen (food access, pipe penetrations, warmth), the basement or crawlspace (primary entry points, storage disturbance), and the utility room or furnace room (warm, dark, rarely entered). In heritage East Vancouver and Burnaby homes, behind the stove and inside the toe-kick cavities are the highest-frequency single locations. In newer Richmond and Surrey homes with slab-on-grade construction, the entry pathway is usually through garage-to-interior door gaps and the utility room where the gas line enters.

How to

Home mouse-sign walk-through — Metro Vancouver

A systematic 20-minute walk-through that identifies active mouse sign without missing the zones homeowners typically skip.

1
Kitchen: check under, behind, and inside
Pull out the stove and refrigerator — droppings accumulate in the motor cavity of fridges and in the grease trough behind stoves. Open every base cabinet and look at the back panel where pipes enter. Check the toe-kick space along the base of cabinets. Look on top of the dishwasher kickplate.
2
Pantry and food storage
Look for gnawed cardboard packaging, powdery debris below shelves, and droppings clustered near food storage. House mice almost always chew soft plastic and cardboard before glass or rigid containers.
3
Basement utility room
Inspect around the hot-water heater, furnace, and electrical panel. Check the wall where the water service and gas line enter. Look for rub marks on baseboards and corners.
4
Crawlspace (if accessible)
Wear an N95 and gloves. Look for droppings, runway smudges on insulation vapour barrier, and any nesting material (shredded paper, insulation fibres, plant material).
5
Attic hatch (if accessible)
Open the hatch and shine a flashlight across the insulation surface. Look for runway tracks in blown insulation and droppings along the ceiling joist lines. Mouse droppings scattered widely across insulation are a different pattern from roof rat runway droppings.

The 48-hour paper test is a good field-expedient confirmation: tape a piece of paper over a suspected entry point inside a cabinet at night and check in the morning. Torn, moved, or nibbled paper is confirmation. You can also dust a thin layer of flour along a suspected runway between the wall and a major appliance — mouse footprints in the flour the next morning are conclusive. These are simple techniques that tech teams use in conjunction with more systematic inspection — and they're valid for homeowners as a first pass before deciding whether to book a professional.