Written by a Zeus Services Certified Technician
All Zeus Services technicians hold BPCA (British Pest Control Association) certifications and undergo continuous professional development. Our advice is based on real-world experience treating thousands of properties across London.
Why Identifying Mice Early Matters
A single female mouse can produce up to 60 offspring per year. What starts as one or two mice in October can become a full infestation by December. The earlier you identify the problem, the less damage is done — to your property, your food supplies, and your peace of mind.
The 8 Most Reliable Signs of Mice
Droppings
Mouse droppings are 3–6mm long, dark brown or black, and pointed at both ends — similar in shape to a grain of rice. You will typically find them along skirting boards, behind appliances, inside cupboards, and in loft insulation. Fresh droppings are soft and dark; older droppings become dry, grey and crumble easily. Finding a high volume in one area indicates a nesting site nearby.
Scratching Sounds at Night
Mice are primarily nocturnal. If you hear light scratching, scurrying or gnawing sounds in the walls, ceiling or under floorboards between 10pm and 4am, this is one of the strongest indicators of an active infestation. The sounds are typically rapid and irregular — distinguishable from settling pipe sounds which are slower and more rhythmic.
Gnaw Marks
Mice constantly gnaw to keep their incisor teeth worn down. Look for gnaw marks on food packaging, wooden skirting boards, cable insulation, furniture legs, and even soft concrete. Fresh gnaw marks are pale and light-coloured; older marks turn yellow-brown. Gnawed electrical cables are a serious fire risk and one of the most important reasons to act quickly.
Ammonia Smell
Mouse urine has a strong, sharp ammonia odour that becomes more noticeable as an infestation grows. In enclosed spaces — kitchen cupboards, airing cupboards, under-sink areas, loft spaces — the smell can be quite pronounced. If you notice an unexplained ammonia-like smell that does not have an obvious source, treat it as a serious warning sign.
Grease Marks (Smear Marks)
Mice follow the same routes repeatedly, typically running along walls and skirting boards. Their fur carries natural grease and dirt which transfers to surfaces over time, leaving dark, greasy smear marks. These are often visible at entry points, along pipe runs, and at the edges of floorboards. Smear marks indicate an established, regular route — meaning mice have been present for some time.
Nesting Material
Mice build nests from soft materials they shred and collect — insulation, cardboard, fabric, paper, and plant material. Nests are typically found in quiet, dark, undisturbed areas: inside wall cavities, behind refrigerators and washing machines, in loft insulation, and in rarely-opened storage boxes. A nest is a definitive sign of an established infestation rather than a single stray mouse.
Footprints and Tail Drag Marks
In dusty areas — lofts, basements, behind large appliances — you may be able to see mouse footprints (four-toed front feet, five-toed back feet) and a thin continuous line from the tail. A practical test: dust a patch of flour or talcum powder near a suspected entry point overnight. Mouse tracks in the morning confirm active movement.
Visible Mice (Day or Night)
Seeing a mouse during daylight hours often indicates a large infestation — mice are naturally cautious and primarily nocturnal, so daytime sightings usually mean competition for space and resources has forced some mice to become more active during the day. A single nighttime sighting does not always mean a large infestation, but should still be investigated immediately.
What to Do if You Suspect Mice
Do not attempt to seal entry points before the infestation is eliminated — you risk trapping mice inside the property where they will cause more damage and die, creating further odour problems.
Professional treatment involves three stages: eliminating the current population with professional-grade rodenticide bait stations, proofing all identified entry points using stainless steel mesh, expanding foam and mortar, and a follow-up visit to confirm complete elimination.
Zeus Services offers same-day appointments across all London boroughs. All rodent proofing work is backed by our industry-leading 2-Year Warranty — the longest in London.