Mice in the House This Autumn: The Signs to Look For and What to Do First

This is a collaborative post

Mice start moving into houses from late September, once the nights turn cold and food in hedgerows and fields becomes harder to find. In rural Dorset the usual visitor is the wood mouse. It lives outdoors for most of the year and only heads indoors when the temperature drops. House mice are more common in towns. Either kind can fit through a gap of around 6mm, roughly the width of a pencil, so even a well-kept home can let one in.

A single mouse is easy to deal with. A few weeks later, after a litter or two, it is a much bigger job, so it pays to act on the first signs.

The signs to look for

Droppings. These are usually the first thing people notice. Mouse droppings are small, dark and rod-shaped, about 3 to 6mm long, and turn up along skirting boards, at the back of kitchen cupboards and behind the cooker or fridge. Larger droppings with blunter ends may point to a rat instead, which needs a different approach. If you are unsure, PestBuddy's guide to telling mice from rats explains the differences.

Noises at night. Mice are most active after dark. Light scratching or scurrying inside walls, above ceilings or under floorboards, especially late in the evening, is a common early sign.

Gnaw marks. Look for small, neat holes in cereal boxes and packets, and for chewed edges on skirting boards, cables or the corners of cupboard doors.

Nests. Mice build nests from shredded paper, fabric and loft insulation in quiet, warm places. Airing cupboards, lofts and the space behind kitchen units are worth checking.

Smell. A stale, slightly ammonia-like smell in an enclosed space can mean there are several mice nearby.

What to do first

1. Take away food and water

Mice settle where food is easy to reach. Keep dry food in sealed glass, metal or hard plastic containers. Wipe up crumbs at the end of the day, and avoid leaving pet food down overnight. Bird seed and chicken feed should be stored in a metal bin with a tight lid. Spilt seed under garden feeders also draws mice towards the house.

2. Find and close the gaps

Walk around the outside of the house and check where pipes and cables enter the walls. Look at the bottom of doors, at damaged air bricks, and at the gap where the garage meets the house. Inside, check behind the boiler and under the kitchen sink.

Small holes can be packed with wire wool and then sealed with filler or a suitable sealant. Expanding foam on its own is not enough, as mice chew straight through it. A brush strip along the bottom of external doors closes another common route. Proofing matters more than anything else on this list, because any mice you remove will simply be replaced if the way in stays open.

3. Set traps in the right places

Once the gaps are closed, deal with any mice already inside. Mice tend to run along walls, so place traps flat against the skirting where you have found droppings, with the trigger end facing the wall. Several traps set a short distance apart work better than one. A small amount of peanut butter or chocolate spread makes a good bait, and it is harder to steal than cheese.

If you have children or pets, choose enclosed traps, or place standard traps inside a lidded box with an entrance hole, so that only a mouse can reach the trigger. Kits that supply the traps and boxes together, such as the mouse trap and box kit from PestBuddy, make this simpler. Live-catch traps are another option. They should be checked at least once a day, since a trapped mouse will become distressed, and the mouse should be released well away from the house.

Rodenticide baits are a later option, used only if proofing and trapping have not solved the problem. They must go in tamper-resistant bait stations, out of reach of children, pets and wildlife. Use biocides safely. Always read the label and product information before use.

4. Check, clean and keep watching

Check traps every day. Wear disposable gloves to handle a caught mouse: place it in a plastic bag, seal it, and put that inside a second bag before it goes in the outside bin.

Droppings should be sprayed with disinfectant and wiped up. Sweeping or vacuuming them dry is best avoided, since this can lift dust into the air. Afterwards, wash your hands thoroughly.

Keep the traps in place until a full week has passed with no new droppings and no catches. Then check the same spots again in a month, as a second mouse often follows the first.

When to call a professional

DIY methods work well for a small problem caught early. Call in a qualified pest controller, ideally a member of the British Pest Control Association (BPCA), if:

• there are signs of mice in several rooms or on more than one floor

• mice keep coming back after you have proofed the house and trapped for several weeks

• someone in the house is elderly, very young or unwell

• the signs suggest rats in the house, not mice

October and November are the busiest months for mice moving indoors. An hour spent checking for gaps now is far easier than dealing with a settled family of mice in the middle of winter.