Scratching in the Walls at Night - Could It Be Mice?

Why Mice Are in the Wall at All

A cavity wall has a continuous vertical void running the height of the building, and a stud wall has one between every pair of studs. Both are warm, dark, protected and connected to the floor void below and the ceiling void above.

Insulation makes it better rather than worse from a mouse’s point of view: soft, warm nesting material in a space nothing else enters. A cavity is not somewhere mice pass through. It is somewhere they live.

What Mouse Noise Sounds Like

Light, fast and intermittent. A rapid scratching or rustling, a few seconds at a time, starting after the house goes quiet and heaviest in the first few hours of darkness. It often seems to move along the wall as you listen.

Rats are heavier — a drag or a thump, and audible gnawing. Squirrels are daytime and heavier still. Birds are first thing in the morning, scrabbling and cheeping, and usually at the eaves rather than mid-wall.

The Non-Animal Explanations Worth Ruling Out

Water pipes in a stud wall tick and knock as they heat and cool, on the heating timer rather than the clock. Timber studs and joists creak with temperature change, often at the same time each evening.

The test is correlation. Noise that follows the heating coming on or the temperature dropping is not an animal. Noise that follows sunset and stops when you bang the wall is.

How to Narrow Down Where

Listen against the wall at different heights with a glass or just an ear. Mice using a cavity run vertically as well as horizontally, so the noise may be nowhere near where they are getting in and out.

Then look for the evidence at the ends of the run: droppings in the airing cupboard, behind the kitchen units, in the understairs cupboard, or at the top of the wall in a bedroom wardrobe. Where the droppings are is where the wall opens into the house.

Why You Cannot Fix It From the Room

Putting bait in the room does very little, because the mice are not in the room — they are in the wall and coming out at specific points. Treatment goes to those points and along the runs.

And do not seal the wall while they are in it. A mouse sealed into a cavity dies in the cavity, and you will smell it for a fortnight. Treatment first — £190 for a flat, £240 for a house, follow-up included — then proofing.