Mice in the house: signs, risks and how to control them

The house mouse is one of the most common pests in British homes and businesses. It is present all year, but the calls rise sharply in autumn, when food outdoors runs short and mice start looking for somewhere warm. Here is how to recognise them, why they matter, and what it takes to deal with them.

01Why mice come indoors in autumn

In summer, most mice live outside. There is food in hedgerows, gardens and fields, cover from vegetation and no need for central heating. As the weather cools, the vegetation dies back and food becomes scarce. Mice do not hibernate, so they look for shelter and something to eat, and houses, garages and commercial buildings offer both.

A hungry mouse takes more risks, and that is usually what brings it into the kitchen. Once inside, it can live comfortably in wall cavities, under floors, behind kitchen units and in the loft, coming out at night to feed.

02What a house mouse looks like

The house mouse (Mus musculus) is small, with a body of about 7 to 9.5cm and a tail of roughly the same length. Its fur is brownish grey, a little paler underneath, and it has large ears and small eyes. Wood mice, which also come indoors, are a warmer sandy brown with bigger eyes and ears and a lighter belly. Our British mice identification guide covers the differences.

03Signs of mice

• Droppings. Dark and rod-shaped, about 3 to 6mm long, often under sinks, in drawers and cupboards, and along the edges of rooms.
• Gnawing. Small, neat holes in food packaging, and chewing on skirting boards, plastic and cables.
• Noise. Light scratching and scurrying in walls, ceilings and under floors, mostly at night.
• Nests. Shredded paper, fabric or insulation gathered into a tidy ball in a hidden corner.
• Smell. A stale, musky smell from mouse urine, strongest in enclosed spaces such as cupboards.
• Tracks and smears. Footprints and tail marks in dust, and faint dark marks along regular runs.
• Pets. Cats and dogs fixing on a particular cupboard, appliance or patch of skirting.

Much larger droppings, heavier movement or gnawing on timber and pipework suggest rats rather than mice. Our guide on telling rats from mice explains what to look for.

04Why mice need dealing with

• Contamination. Mice urinate as they move and leave droppings wherever they feed. They can carry bacteria such as salmonella and listeria and transfer them to worktops, cupboards and stored food.
• Allergies. Mouse droppings, urine and shed skin can trigger allergies and make asthma worse, and the allergens can linger after the mice have gone.
• Damage. Mice gnaw constantly to keep their incisors worn down. Chewed electrical cables are a fire risk, and stored belongings, insulation and food packaging all suffer.
• Parasites. Mice can bring fleas and mites into the house with them.

05How fast mice breed

A female house mouse can have five to ten litters a year. Pregnancy lasts about three weeks, she can mate again soon after giving birth, and the young are able to breed themselves from around six weeks old. That is why a mouse problem that is ignored for a month or two is usually a bigger one by the time anyone acts.

06What you can do

• Remove the food. Store dry food in sealed glass, metal or rigid plastic containers, clear crumbs and spills, and pick up pet food overnight.
• Reduce the clutter. Piles of cardboard, paper and fabric in garages, lofts and cupboards make ideal nesting sites.
• Trap rather than poison. For one or two mice, snap traps set against walls along their runs work well. Poison in a house risks mice dying out of reach, and it is a hazard to children and pets if it is not placed with care.
• Clean up safely. Wear gloves, dampen droppings with disinfectant before wiping them up, and never sweep or vacuum them dry. Our clean-up guide covers this step by step.

Keeping them out for good is about proofing. Our guide to keeping mice out of your home covers where they get in and how to close the gaps.

07What professional control involves

We start with a survey: where the mice are active, where they are nesting, how many there are and, most importantly, how they are getting in. Treatment is planned around what we find, using traps, bait in secure tamper-resistant stations, or both, placed where children and pets cannot reach them. Once activity stops, we proof the entry points so the next mouse cannot follow the same route, and check back to make sure the problem has gone.