How do I get rid of mice?

Confirming mice, blocking the way in, and dealing with them — with the entry-point work that determines whether they come back.

Difficulty: intermediate
Time: 3 hr
Read: 2 min
Safety: caution

Short answer

Sealing entry points is what actually solves it — mice get through a gap the width of a pencil. Remove food sources, block holes with wire wool and filler, and set traps along walls where they run. Trapping without sealing means a permanent trapping programme.

Mice come indoors for food and warmth, usually in autumn. Killing the ones inside without closing the route in means more arrive. The entry-point work is unglamorous and it is the part that determines whether the problem ends.

Safety

Mouse droppings and urine can carry disease. Wear gloves, ventilate the area, dampen droppings before cleaning rather than sweeping or vacuuming them dry, and wash thoroughly afterwards. Keep traps and any rodenticide well away from children and pets — rodenticides also poison the animals that eat affected mice, so traps are generally preferable.

What you'll need

Wire wool and filler or expanding foam
Snap traps
Gloves
Disinfectant
Torch (optional)

Step by step

Confirm it is mice: droppings the size of rice grains, gnawing, and scratching at night.Droppings along skirtings and in cupboards are the clearest sign. Rat droppings are much larger.
Find the entry points with a torch, at floor level.Around pipes, under kitchen units, behind appliances, at airbricks and where cables enter. A gap the width of a pencil is enough.
Block every gap with wire wool packed in and sealed over with filler.Mice gnaw through foam and sealant alone. Wire wool is what stops them, and the filler holds it in place.
Remove food sources — store dry goods in sealed containers.Cardboard and plastic packaging is no obstacle. Glass, metal or thick plastic containers are.
Clean up crumbs, pet food and bird food.Pet food left down overnight is one of the most common attractants.
Set snap traps against walls, perpendicular to the skirting.Mice run along walls rather than across open floor. Traps in the middle of a room catch nothing.
Bait with chocolate, peanut butter or something sticky.Cheese is much less effective than the folklore suggests. Something they cannot carry away works best.
Clean droppings safely: dampen first, wear gloves, and disinfect.Never sweep or vacuum dry droppings — it makes the particles airborne.
Keep checking and re-sealing.New gaps open as buildings move. An annual check around pipe entries prevents most recurrences.

Tips

If you can hear them in a cavity or roof space but cannot find the entry, or if the problem persists, a professional pest controller is worth the cost.
Rodenticides poison the predators that eat affected mice, and they can leave a dead mouse somewhere inaccessible. Traps avoid both problems.
Ultrasonic repellers have very little evidence behind them and are not a substitute for sealing.

Common mistakes

Trapping without sealing entry points — More mice simply arrive. The sealing is what ends the problem.
Using expanding foam alone to block a hole — Mice gnaw straight through it. Pack wire wool in first.
Sweeping or vacuuming dry droppings — It makes particles airborne. Dampen them first, wear gloves and disinfect.

Questions people ask

How small a gap can a mouse get through?

Roughly the width of a pencil — around 6mm. That is why sealing has to be thorough, and why gaps around pipes and cables are the usual route in.

Are traps or poison better?

Traps, in most domestic situations. Rodenticides risk poisoning pets and the predators that eat affected mice, and a poisoned mouse often dies somewhere inaccessible.