About this guide
This guide covers the key signs of a rat infestation in UK properties — droppings, gnaw marks, burrows, grease smear marks, sounds, and footprints — explains how to interpret what you find, and describes when professional treatment is needed. The page supports Apex Pest Control Ltd's rat control service by helping property owners identify an infestation accurately before choosing a professional pest control provider.
Brown rats (Rattus norvegicus) are cautious, largely nocturnal animals that tend to avoid exposure. By the time rats are seen in daylight, a population is usually already well-established. Knowing the signs of rat activity — most of which are detectable long before the rats themselves are visible — enables early identification and intervention before numbers increase and damage accumulates.
Droppings
Brown rat droppings are the most reliable early indicator of activity. They are dark brown to black, capsule-shaped, and typically 12–18 mm long — approximately the size and shape of a large olive stone. Droppings are deposited at high density along travel routes, near food sources, and in harbourage areas. A single brown rat produces up to 40 droppings per night.
Fresh droppings are dark, soft, and moist. Older droppings dry, harden, and lighten in colour. Finding fresh droppings alongside older ones confirms ongoing activity. The quantity of droppings gives a rough indication of population size — dozens of droppings suggest an established infestation, not a single visitor.
Do not confuse brown rat droppings with mouse droppings. Mouse droppings are much smaller (3–6 mm), spindle-shaped with pointed ends, and typically found in greater quantities relative to population size. Squirrel droppings are barrel-shaped and approximately 8 mm.
A single brown rat deposits up to 40 droppings per night along its regular travel routes, making fresh droppings the most reliable early sign of an active infestation.
— BPCA Pest Technician Reference Manual, 2023
Gnaw marks
Rats must gnaw continuously to wear down their permanently growing incisor teeth. Gnaw marks are found on wood, plastic, lead pipe, soft masonry, electrical cable insulation, food packaging, and structural timbers. Brown rat incisors leave parallel grooves approximately 4 mm wide. Fresh gnaw marks are pale and light-coloured; older marks darken as the wood oxidises. Active gnawing on electrical cables is a significant fire risk — it is estimated that approximately 25% of electrical fires of unknown cause may be attributable to rodent gnawing.
Characteristic locations for gnaw marks: the base of external doors, corners of kitchen cabinet plinths, around pipe penetrations through walls, airbrick surrounds, and the edges of floor joists in subfloor spaces.
Gnaw damage to electrical cables by rats is a genuine fire risk. If you find gnaw marks on cables in loft spaces, subfloor voids, or behind appliances, treat this as an urgent safety matter — have the wiring inspected by an electrician before using the affected circuit, and arrange rodent control promptly.
Smear marks
Rats travel the same routes repeatedly and press against walls, beams, and other surfaces as they move. The oils and dirt in their fur leave dark greasy smear marks along these habitual pathways — known as rat runs. Smear marks are found along skirting boards, wall junctions, the base of beams, around pipe penetrations, and at the entry points of burrows. They are one of the most reliable signs of an established population using a fixed travel route.
Fresh smear marks are greasy and dark. Older marks dry and may crack. On a smooth wall surface, smear marks form a continuous line; on rough surfaces such as brickwork, they appear as a series of dark patches.
Burrows and nests
Brown rat burrows are typically 6–9 cm in diameter — roughly the width of a cricket ball. They are most commonly found in soft soil along the base of fences, walls, compost heaps, beneath decking, in embankments, and under concrete slabs. Active burrows have smooth, worn entrances with fresh soil displacement and sometimes cached food material nearby. Collapsed or cobwebbed entrances indicate disused burrows.
Indoors, rats nest in loft insulation, cavity wall spaces, beneath floorboards, and inside wall voids. Nest material includes shredded insulation, fabric, paper, and plant matter. The presence of a nest indicates the rats are breeding on site, which significantly increases the urgency of treatment.
Sounds and other signs
Sounds: Scratching and scrabbling sounds in walls, ceilings, and loft spaces — most commonly heard at night when rats are most active — are a strong indicator of activity within the building structure. The sounds are heavier than those produced by mice and tend to follow fixed pathways.
Footprints: In dusty loft spaces, cellars, garages, or shed floors, rat footprints may be visible. The hind foot of an adult brown rat leaves a print approximately 25–35 mm long with four visible toes and a central pad. Tail drag marks may also be visible in fine dust or mud.
Food damage: Characteristic nibbling of stored food, gnawed through packaging, and scattered food debris beneath storage shelving. Rats are omnivores and will consume grains, cereals, fruit, meat scraps, and pet food with equal readiness.
Pet behaviour: Dogs and cats often detect rat presence before humans do. Persistent scratching at walls, unusual interest in specific floor areas, or agitated behaviour near a particular wall or cupboard can indicate hidden activity.
When signs indicate a professional is needed
Any sign of active rat infestation in a domestic or commercial property warrants professional assessment. Consumer bait and traps can manage a minor mouse problem but are rarely sufficient for an established rat infestation — particularly where there are signs of burrowing, nesting within the structure, or gnaw damage to cables or pipework.
On commercial properties, particularly food premises, any confirmed sign of rat activity requires immediate action under food safety and public health obligations.
Frequently Asked Questions
What do brown rat droppings look like?
Brown rat droppings are dark brown to black, capsule-shaped, and 12–18 mm long — approximately the size of an olive stone. Fresh droppings are soft and moist; older ones harden and lighten. A single brown rat produces up to 40 droppings per night, so an active infestation leaves large quantities along habitual travel routes.
How do I tell the difference between rat and mouse droppings?
Brown rat droppings are 12–18 mm long and capsule-shaped. Mouse droppings are much smaller (3–6 mm), spindle-shaped with pointed ends, and typically found in larger quantities relative to population size. If droppings are smaller than a grain of rice, they are likely mouse droppings; if olive-stone sized, they are from a brown rat.
What do rat smear marks look like and where are they found?
Smear marks are dark, greasy streaks left by rat fur along habitual travel routes — walls, skirting boards, beam edges, pipe runs, and burrow entrances. They are one of the most reliable indicators of an established rat population using fixed pathways. Fresh marks are greasy; older ones dry and may crack.
Are scratching noises in walls always rats?
Not necessarily — squirrels, mice, and birds can also produce scratching sounds in wall cavities and loft spaces. Rat sounds are typically heavier and follow fixed pathways. Context matters: if you also find capsule-shaped droppings, gnaw marks, or smear marks, the cause is more likely rats. A pest control survey will confirm the species.
What size is a rat burrow entrance?
Brown rat burrow entrances are typically 6–9 cm in diameter — roughly the width of a cricket ball. Active burrows have smooth, worn entrances with fresh soil displacement. They are most commonly found at the base of walls, fences, compost heaps, beneath decking, and in garden embankments.
Can I have rats without seeing them?
Yes. Brown rats are largely nocturnal and cautious — they actively avoid exposure during daylight hours. Most infestations are identified through secondary signs (droppings, gnaw marks, smear marks, sounds) long before rats are seen directly. Daylight sightings usually indicate a well-established, overcrowded population.
How quickly does a rat infestation grow?
Brown rats reach sexual maturity at approximately 5 weeks and have a gestation period of 21–23 days, producing litters of 6–11 pups. Under favourable conditions, a pair of rats can produce several litters per year. A small initial incursion can become a significant infestation within a few months if left untreated.