How do I tell whether I have mice or rats?

The identification matters far more than it sounds. Mice explore constantly and leave evidence everywhere, so a small population looks alarming. Rats are cautious, travel established routes and leave less obvious evidence, so by the time it is obvious there are usually more than you think. The two need different traps, different bait and a different level of response.

Safety

What you'll need

• A torch
• Disposable gloves
• A dusting of plain flour or talc, to read tracks (optional)

Step by step

1. Measure a dropping.This is the most reliable single test. Mouse: 3-6mm, thin, pointed at the ends, dark, and scattered — a mouse produces dozens a day as it moves. Rat: 12-19mm, thick, blunt or rounded ends, usually deposited in groups at feeding or resting points.
2. Note where the droppings are.Mice leave them everywhere, including on worktops, in drawers and inside packets. Rats leave them along runs and in concentrated latrine areas, often behind or under something.
3. Look for smear marks.Rats travel the same route repeatedly and their greasy fur leaves dark shiny marks along skirtings, at the base of walls, over pipes and at the edges of a hole. Heavy smearing indicates rats and an established run, not a passing visitor.
4. Look at the size of the holes.A mouse gets through roughly 6mm — about the width of a pencil. A rat needs about 25mm and will enlarge a smaller hole by gnawing. A gnawed hole the size of a fifty pence piece is a rat hole.
5. Listen, and note the time and the weight.Light, fast scurrying and high scratching, mostly at night, in a cavity or loft: mice. Heavier movement, thumps, and gnawing you can hear through a wall: rats or squirrels. Daytime scampering with heavy landings in a loft is usually squirrels.
6. Check the gnawing.Mice nibble small ragged holes in packets and skirting. Rats gnaw hard and purposefully, and will take on wood, plastic pipe, lead and cable. Chewed cable is a fire risk and moves the job up the urgency list immediately.
7. Use a tracking dust to confirm.A light dusting of plain flour or talc across a suspected run overnight shows footprints and a tail drag. It tells you both what it is and exactly where it travels, which is where traps have to go.
8. Note the smell.Mice leave a distinctive stale, ammoniac, musky smell in an enclosed cupboard. A strong rat presence smells stronger and more sour. A sudden intense smell of decay usually means something has died in a cavity.
9. Check for a nest.Shredded paper, insulation, fabric and packaging, in an undisturbed corner: behind an appliance, in a loft, under floorboards or in the back of a cupboard. Finding it localises everything else.
10. Decide the response from the answer.Mice: seal the entries, remove food, trap along runs. Rats indoors, rats in numbers, or any sign of gnawed cable or a burrow near a drain: get a professional in, and report a suspected defective drain to your water company or the council.

Tips

• One clear dropping identification saves buying the wrong traps twice. Mouse traps do not reliably kill rats and set the animal up to become trap-shy.
• Squirrels are commonly mistaken for rats in a loft. Squirrel droppings are similar in size to rat but rounder, and squirrels are noisy in daylight and silent at night.
• If you find rat burrows in the garden near a manhole or an inspection chamber, a broken drain is a very common cause and is often the water company's responsibility to investigate.

Common mistakes

• Assuming any large dropping is a rat — Squirrels, hedgehogs and even a neighbour's cat produce droppings people misread. Size, shape, location and the pattern of noise together give a reliable answer where one alone does not.
• Clearing up the evidence before identifying it — Droppings, smears and gnaw marks are the diagnostic information. Photograph and measure before cleaning, or you have to wait for it to reappear.

If it doesn't work

Questions people ask