How to tell rats from mice in a loft

Written by Avon Pest ControlPublished 13 August 2026Reading time: 3 minutes

Rats and mice are both common in Midlands lofts, and unless you actually see one, telling them apart from the signs alone takes more than a guess. Here is what genuinely tells them apart, what a photo or a phone call can and can't confirm, and what to do next.

Start with size — but don't stop there

A fully grown rat is a different animal to a mouse: a rat's body typically runs 20–27cm, not counting the tail, against 6–9cm for a house mouse. The complication is a young rat, which can be close to mouse-sized for its first few weeks. Size alone, especially from a fleeting glimpse in poor light, is not conclusive on its own.

Droppings are a strong clue, not a certain one

Droppings are genuinely useful: rat droppings are roughly 12–20mm, capsule-shaped with blunt ends; mouse droppings are much smaller, around 3–6mm, and more rod-shaped with pointed ends. It's a strong indicator rather than a guaranteed test — a juvenile rat's droppings can be mistaken for an adult mouse's — which is why we confirm on site rather than from a description alone where it matters.

Droppings can carry bacteria and viruses, including those linked to Weil's disease and hantavirus. Don't sweep or vacuum them dry, and avoid close inspection. If you need to clear a small amount before we arrive, dampen the area first and wear gloves.

What the noise tells you

Rats and mice are both mainly active at night, so scratching or movement overhead after dark points to one or the other rather than to a grey squirrel — which, despite being a common suspect for loft noise, is active during the day. Rat movement tends to be heavier and slower; mice are lighter and quicker, often in short bursts.

Gnaw marks and behaviour

Rats gnaw to get through structural material — timber, pipework, even soft metals — leaving larger, deeper marks. Mice gnaw more at surface level, on packaging and stored fabric. Mice also investigate anything new in their space quickly, which is part of why they're often trapped within days; rats are naturally cautious of unfamiliar objects and can avoid a trap for a week or more before taking it.

If it turns out to be a grey squirrel

Grey squirrels are a non-native invasive species in the UK, and under the Wildlife and Countryside Act 1981 you cannot legally release one back into the wild once it has been trapped — it must be humanely dispatched or handed to a vet. That Act is the source for this specific legal point; it is not a general guide to identifying rats or mice, which is why we haven't leaned on it for the rest of this article.

What closing the gap doesn't do on its own

Proofing the entry point is essential, but sealing it before dealing with what's already inside can trap the animals in the building rather than keep them out. Control and proofing are sequenced deliberately — clear first, then close the route — not treated as the same step.

When to call rather than guess

None of this replaces a proper survey. Droppings, gnaw marks and noise all point in a direction, but confirming what you actually have — and more importantly, where it's getting in — is what a technician does on site. If you're not sure what you're looking at, a photo usually settles it faster than trying to match it against a list.

Rats and mice are treated differently, so once you know which one you're dealing with: rat control and mouse control each have their own page covering signs, process and proofing.