House Mouse

Mus musculus

Size65–95 mm body length

Colony Size1–500

Active Season:Active year-round indoors. Peak indoor movement occurs during first frost (September-October in most of Canada) as mice seek thermal refuge. This 'fall pressure' is the most common time for new infestations.

Small grey-brown rodent that thrives in human structures. Canada's most common indoor rodent pest.

Anatomy

Anatomical Details

Identification

ColourGrey-brown fur, lighter underside, nearly hairless tail

Size65–95 mm body length

Distinguishing Features

Large ears relative to head size
Pointed snout
Tail equal to or longer than body length
Uniform grey-brown tail (unlike the bi-colored tail of the Deer Mouse)
Small droppings (3-6mm) with pointed ends
Distinctive musty odour (acetamide) detectable in enclosed spaces

Biology

Lifecycle

Sexual maturity at 6 weeks. Gestation 19-21 days. 5-10 litters/year with 5-6 young each.

Diet

Omnivorous but prefer grains and seeds. 'Nibblers' by nature—visit 20-30 food sites per night, consuming only 0.1g per visit. This explains why baits sometimes fail when competing food sources are present. Need only 3ml water daily—can survive on food moisture alone.

Nesting

Build nests in micro-environments near heat sources—behind refrigerators, inside oven insulation, near water heaters. Nests are constructed from 'soft' human materials: shredded fiberglass insulation, yarn, paper, or fabric, formed into a ball about 10-15cm in diameter. Always within 3-10m of a food source.

Signs of Infestation

Droppings

Small dark pellets (3-6mm), pointed at ends. 50-80 per mouse per day.

Gnaw marks

Small tooth marks on food packaging, wood, wires, plastic.

Rub marks

Dark greasy smears along walls and baseboards from body oils.

Scratching sounds

Nocturnal activity in walls, ceilings, under floors.

Where They Nest

Kitchen cabinets and pantries
Behind appliances
Wall voids near heat sources
Cluttered storage areas
Garage and utility rooms

Common Nesting Sites

Nesting Site Details

Distribution in Canada

Found in all provinces wherever humans live. Primarily indoor pest.

Regional Prevalence

High

Moderate

Low

Rare/Absent

Active Season

Active year-round indoors. Peak indoor movement occurs during first frost (September-October in most of Canada) as mice seek thermal refuge. This 'fall pressure' is the most common time for new infestations.