First the danger, mice are more of a problem in buildings because they live indoors. They are more liable to cause fires by gnawing cables and they can damage insulation in animal housing causing costly heat loss and expensive replacement.

Mice carry diseases such as salmonella and they can transmit a type of Leptospirosis, but not Weil’s disease. Their continual dribble of urine contaminates food and feedstuffs. They are a particular problem in poultry units and pig housing and a very real pest in grain stores, warehouses, shops, hospitals, and domestic premises.

Being so small they are very easily carried, unnoticed, in egg boxes, food packaging, laundry baskets, etc. Entering a new location through gaps as small as 6mm, mice build nests which are hard to find, populating an area with new colonies quickly with devastating effect. Because mice can reach sexual maturity 42 days after birth, population grow much faster than those of rats, which take about twice the time to reach maturity.

The difficulty of preventing access, coupled with the rapid population growth and natural dispersal of mice, means that a large building may contain a number of colonies, each of which must be treated as a separate infestation and control needs to be tackled systematically.

Mus domesticus

Common names: House mouse

Adult Weight: 15 grams

Length (head + body): 60-90mm

Length (tail): 80-100mm, usually longer than the head & body

Fur & colour: Brownish grey. Lighter shades occur.

Ears & hearing: Large with some hairs. Excellent sense of hearing.

Eyes & sight: Small, poor sight, colour blind

Snout, smell and taste: Pointed, excellent sense of smell & taste

Droppings: Scattered, rod shaped, 3-6mm long

Habits & habitat: Sometimes burrows. Lives indoors & outdoors but is almost unknown in sewers. Nest generally within stored materials but may burrow. Climbs. Eratic in habit. Inquisitive towards new objects. Range 1.5 – 5 metres.

Feeding habits: Nibbles. Prefers cereals. Consumes 3grams per day. Unlike rats, can survive with very little water & often obtains sufficient water in food without the need to drink.

Life cycle: Span 9-12 months

Sexual maturity: 7 weeks. Litter size 5-6 offspring.

Maximum reproduction rate: 8 litters per year

A female mouse and her offspring can theoretically produce 15,000 mice per year.

A mouse produces 30,000 droppings and 1 litre of urine per year.

Rats and mice can spread salmonella through their droppings.

For every 1kg of food eaten by rats and mice a further 3kg has been contaminated.

Rats require a separate source of drinking water, mice can survive on the moisture in food.

A mouse will fit through a gap the width of a pencil (10mm to 15mm)