12 Signs of a Rodent Infestation in Your NYC Home

1. Droppings

Droppings are the most reliable sign of active rodent infestation and the fastest way to determine which species you're dealing with. Location matters as much as the droppings themselves.

Mouse droppings are 1/4 inch long, pointed at both ends, and look like dark grains of rice. They're found along baseboards, behind appliances, inside cabinet bases, and in pantry corners — wherever mice travel and nest. Fresh droppings are dark and slightly shiny. Old droppings are gray, crumbly, and fall apart when touched.

Rat droppings are 3/4 inch capsule-shaped with blunt ends — noticeably larger. Norway rat droppings concentrate near floor level, in basements, and along wall-base runs. Roof rat droppings appear in elevated spaces: attic insulation, along ceiling joists, near roofline penetrations.

If you're finding droppings but not sure of the species, our inspection will confirm based on size, shape, and location.

2. Gnaw Marks

Rodents gnaw constantly — not just for food access but to wear down continuously growing incisors. Fresh gnaw marks show light-colored exposed wood with sharp edges. Old gnaw marks are darker and the edges are worn smooth.

Mice typically gnaw through food packaging — cardboard boxes, soft plastic bags, cereal boxes — and the wooden edges of cabinet interiors. Rats gnaw through harder materials: wood baseboards, soft metals like lead pipes, and rigid plastic containers. Gnaw marks on electrical wiring in attics or wall voids are a fire risk and should be treated as urgent.

The location of gnaw marks helps identify the entry point. Gnaw marks at floor level near walls indicate active travel routes. Gnaw marks at utility penetrations — where pipes enter through walls — indicate active entry points that need sealing.

3. Rub Marks

Rats have sebaceous oil in their fur that leaves greasy brown smear marks on surfaces they run repeatedly. These rub marks appear as dark brown streaks along baseboards, the sides of pipes, and any surface a rat runs against consistently.

Fresh rub marks are sticky and dark. Old rub marks are dry, smudged, and may have accumulated dirt and dust on top. The presence of rub marks confirms that the pathway is actively used, which helps focus exclusion work on the highest-priority access routes.

Mice leave similar but smaller marks. In heavily infested spaces you'll see these marks along every wall-floor junction.

4. Scratching Sounds

Nocturnal scratching in walls, ceilings, and floors is one of the most common complaints we receive — and one of the most reliable indicators of an active infestation.

The character of the sound helps identify the species. Mouse sounds in walls are light, rapid, and scratchy — often with faint high-pitched squeaking. Rat sounds are heavier and more deliberate — thuds and scraping rather than the light patter of mice. Roof rats in attics produce a running, skittering sound that moves across the ceiling. Norway rats in basements produce heavier scratching and digging sounds.

Sounds at consistent times — shortly after you turn the lights out, in the early hours of the morning — are more diagnostic than occasional isolated noises. Consistent sound patterns almost always indicate an established population, not a single wandering animal.

5. Musty Smells

Active rodent infestations produce a distinctive musty, ammonia-like odor from accumulated urine in nesting areas. This smell is often the first sign noticed in enclosed spaces — basement storage rooms, cabinet interiors, attics — before visible evidence is found.

The odor intensity correlates with infestation severity. A faint musty smell in a cabinet under the sink may indicate a small mouse presence. A strong pervasive ammonia odor in a basement or attic indicates a larger established population with significant urine accumulation in the nesting area.

If you notice this odor in a space you don't access regularly, investigate before disturbing anything. Disturbing nesting material without precautions carries disease risk, particularly if deer mice are present.

6. Nests and Shredded Material

Rodent nests are built from whatever soft material is available — insulation fibers, shredded newspaper, fabric scraps, plant material, or soft packaging. Nests appear as roughly spherical piles of shredded material in warm, dark, undisturbed spaces.

Common nesting locations in NYC buildings: inside cabinet bases, behind refrigerators and dishwashers, in wall-void access spaces at pipe penetrations, in attic insulation, in boxes of stored clothing or seasonal items in closets, and in unused appliances like old ovens or microwaves.

The presence of a nest confirms an established infestation rather than a transient intrusion. Nests with young pups inside indicate active breeding, which requires immediate treatment.

7. Direct Sightings

A mouse or rat seen during the day is a stronger signal than one seen at night. Rodents are primarily nocturnal, and daytime sightings indicate a population large enough that competition for food is pushing animals out of their normal nocturnal activity pattern.

For rats specifically: a rat running across the floor in daylight, or seen near garbage areas during business hours, indicates a substantial population, not an isolated individual. Daytime rat sightings in restaurants, bodegas, or residential buildings are an escalated situation that warrants urgent response.

For mice: seeing a mouse dash across the kitchen at 10pm is common in infested NYC apartments. Seeing mice during the day — especially multiple mice — indicates a larger population than typical.

8. Pet Behavior Changes

Cats and dogs often detect rodents before their owners do. A cat fixated on a specific section of baseboard, an appliance, or a wall corner — particularly a spot they've never paid attention to before — is often tracking a mouse in the wall void behind that surface. Dogs pawing at under-appliance gaps or barking at a specific cabinet may be responding to mouse activity inside.

This behavior is most useful when it appears suddenly in a space the pet normally ignores. Sudden interest in a specific wall corner, appliance gap, or basement area is worth investigating. Pull the appliance out, check behind it, and look for droppings.

9. Greasy Smudges on Walls

Along with rub marks from repeated rat travel routes, you may notice general greasy smudges or darkening along baseboards, behind appliances, or at the base of walls. These accumulate over time from repeated rodent contact and the transfer of oils and debris from their fur and feet.

In kitchens with suspected mouse activity, look at the wall behind the stove and refrigerator — both common mouse travel corridors — for smudging or darkening along the baseboard. Pull these appliances out if accessible.

10. Holes in Food Packaging

Chewed-through food packaging is often the first thing that triggers a call to a rodent control company. Mice particularly target dry goods stored at low heights: cereal boxes, pasta bags, rice bags, granola bars, and similar items. The gnaw hole is typically irregular, with torn edges.

In kitchens with mouse activity, check the lower shelves of pantries and the insides of lower cabinets first. Move everything away from the back of the shelf — mice cache food and sometimes move packaging to wall-adjacent corners near their entry gaps.

11. Tracks in Dust

Dusty surfaces in rarely accessed areas — attic floors, basement utility corridors, behind large appliances — can show rodent footprints. Mouse footprints are tiny (approximately 3/8 inch), with a four-toed front foot and five-toed rear foot pattern. Rat footprints are larger (3/4 to 1 inch) with the same general pattern.

A UV flashlight can reveal urine trails left by mice along travel routes — mice urinate continuously as they move, and the dried urine fluoresces visibly under UV. This technique is useful for confirming active travel routes when droppings and other signs are ambiguous.

12. Burrows Outside

Norway rat burrows outside the building are a direct sign that the exterior rodent pressure on your property is high. Burrows appear as 2-4 inch diameter holes in soil, typically alongside foundations, under stoops, along fence lines, in garden beds, or under pavement edges. Active burrows have clean, unobstructed entrances and loose fresh soil around them. Abandoned burrows have cobwebs at the entrance and compacted soil.

Multiple active burrows near a building's foundation indicate a large outdoor colony with constant interior infiltration pressure. These burrows require exterior treatment as part of any comprehensive control program — interior-only treatment with active outdoor burrow systems will always produce re-infestation.