Most guides to telling these two apart work on noise and droppings. There is a third line of evidence that is often decisive and rarely mentioned, which is what the space smells like.
Why rats smell and squirrels largely do not
It comes down to how each animal uses the space. Rats urinate more or less continuously as they move — it is how they mark and navigate their runs — so an established population saturates the material it lives in. That produces the characteristic ammoniacal, musty, slightly sweet smell that people describe as unmistakable once they have met it.
Squirrels do not do that. They use a roof space as a nest site rather than a territory to be marked, they are in and out through the day, and their droppings are drier and more scattered. A loft with squirrels in it usually smells of nothing much at all.
What each smells like
- Rats. Ammonia over a stale, musty base. Strongest in warm still weather, and noticeably worse near the loft hatch when it is opened
- Mice. Similar in character but lighter and sweeter, and easier to miss
- Squirrels. Generally nothing. Sometimes a faint earthy or animal smell close to a nest, and no ammonia
- Birds. A dusty, feathery smell, and in summer sometimes an insect-infested one from an old nest
- Something dead. Distinct from all of the above, strongest for a week or two and then fading, and worth acting on whatever caused it
A strong ammonia smell from a roof space is a rodent finding, not a squirrel one. If the noise says squirrel and the smell says rats, the sensible conclusion is that both may be present rather than that one of the two tests is wrong.
How to test it fairly
Smell fatigues quickly, so the first few seconds after the hatch opens are the only ones worth trusting. Come to it fresh, from outdoors if possible, open the hatch and pay attention immediately. Warm weather makes everything more obvious; a cold loft in January gives very little away.
It is also worth asking somebody else to do it without being told what to expect. Smell is highly suggestible, and a second opinion with no prompt is worth more than a careful sniff by someone who already has a theory.
What the smell does not tell you
It does not date anything. A roof space that held rats two years ago can still smell of them, because the material holds it. And its absence proves very little in a cold, well-ventilated loft in winter. Treat it as one line of evidence alongside the timing of the noise, which remains the strongest single test.
Questions
There is a smell but no noise. What does that mean?
Possibly a past problem, possibly something dead. Both are worth investigating, and neither resolves itself.
Can a squirrel nest smell?
Faintly and locally, of nesting material rather than ammonia. It is not the smell people describe from a rat-infested loft.
Does the smell come down into the house?
It can, through a hatch, through downlighter openings and along service runs, which is often how people first notice it.
Squirrel Control Cambridge
Squirrel control in Cambridge is £280 fixed cost. Proofing work, where it is needed afterwards, is £180. Call 01502 630 122 and tell us what you have heard or seen.
For squirrel control in Cambridge, call 01502 630 122, or read the Cambridge squirrel control page.