How do I know if it is mice inside the walls or just the building settling?

Building settling produces random creaking or popping sounds, usually when temperature changes. Mice produce rhythmic scratching, gnawing (a rapid rasping sound), and sometimes soft squeaking — almost always between midnight and 4 am when the building is quiet. If you hear it on multiple consecutive nights in the same spot, it is almost certainly mice.

Can mice live inside walls indefinitely without coming out?

No. Mice need food and water daily. They use wall cavities as safe travel corridors and nesting spots, but they must leave to forage. This is why traps placed at the points where they exit the wall — along baseboards, behind appliances, inside cabinets — are effective. A mouse that cannot reach food will leave or die within two to four days.

Is it safe to seal up a gap if mice might still be inside the wall?

It depends on timing. If you seal an entry point during an active infestation without first clearing the mice, you risk trapping them inside. A trapped mouse will die and decompose, causing a serious odour problem for weeks. The correct sequence is: trap first until catch rate drops to zero over several consecutive days, then seal. A professional will sometimes use one-way exclusion devices that let mice exit but not re-enter.

My landlord keeps sending pest control but the mice keep coming back. What are my rights in NYC?

Under NYC Housing Maintenance Code Section 27-2018, landlords are required to keep apartments free of pests. If treatment is not working, you can file a complaint with NYC 311 (HPD will inspect), withhold rent via an HP action in Housing Court, or apply for a rent reduction. Document every communication with your landlord and every pest control visit in writing. Recurring infestations in a shared building usually mean the source — basement, neighbouring unit, or shared chase — has not been addressed.

How long does it take to get rid of mice in walls?

A mild infestation caught early — one or two mice using a wall run — can be resolved in one to two weeks with consistent trapping and sealing. A moderate to heavy infestation in a pre-war building with open chase access typically takes two to four professional visits over three to six weeks. Full resolution requires both trapping out the existing population and exclusion work to prevent reinvasion; skipping either step means the problem returns within months.

Mice in Walls: How to Get Rid of Them in NYC | Bed Bugs Exterminator Bronx

If you live in a New York City apartment, brownstone, or co-op and you are hearing scratching sounds inside your walls at night, you already know something is wrong. That sound — a rapid, light rasping or the dull thud of something moving through a cavity — is almost always house mice (Mus musculus), and in NYC they are extraordinarily common. Understanding why mice end up inside walls, how to confirm it, and what it actually takes to get rid of them will save you months of frustration.

Why NYC Walls Are a Mouse Highway

Mice do not choose to live inside walls because it is cosy. They use wall cavities, pipe chases, and floor-ceiling voids as protected travel corridors between a safe nest and a food source. In NYC, the built environment makes this almost inevitable.

Pre-war brownstones and co-op buildings — anything built before the 1950s — were constructed before modern pest exclusion standards existed. Pipe chases running from the basement to the roof are often open, or closed with materials that have long since deteriorated. Shared walls between apartments mean a mouse entering on the ground floor can reach the fifth floor without ever stepping into an open room. Settled foundations crack. Gas line penetrations leave gaps. The average pre-war Manhattan or Brooklyn apartment has dozens of unintentional openings into the wall system that are invisible unless you are specifically looking for them.

New construction is not immune either. Utility conduits, HVAC plenums, and elevator shafts create similar internal connectivity. Add the density of the city — rubbish collection, restaurant supply deliveries, street-level food waste — and there is constant pressure from the outside pushing mice toward any gap they can find.

How to Know if Mice Are Actually in Your Walls

The clearest sign is sound: scratching, gnawing, or soft scurrying, almost always between midnight and 4 am. Mice are neophobic — cautious of new objects — so they are most active when the building is at its quietest.

Secondary signs to look for:

Droppings near the base of walls, inside kitchen cabinets, behind the stove, or under the sink. Fresh droppings are dark and moist; older ones dry to a dull grey.
Grease rub marks along baseboards and around pipe penetrations, left by the oils in a mouse’s fur as it travels the same route repeatedly.
Gnaw marks on soft materials near wall penetrations — the edge of a cabinet, the caulk around a pipe collar, the corner of a food package stored too close to a gap.
Odour — a faint musky smell in an enclosed space (under a sink, inside a cabinet) that you cannot explain. A stronger ammonia smell indicates a larger or longer-established population.

If you have sounds but no other signs, you may be dealing with one or two scouts. If you have droppings in multiple locations plus sounds, the infestation is already established.

DIY vs Professional Treatment

DIY is appropriate for a very early, isolated incursion — one or two mice, one entry point, one affected room. Set multiple snap traps at the active points (perpendicular to walls, inside cabinets, never in open floor space), bait with peanut butter, and check daily. If you catch mice consistently for three to four days and then the trapping stops, and sounds cease, you may have resolved it.

DIY is not appropriate — and will waste your time — if:

Sounds come from multiple walls or rooms
You find droppings in the kitchen and a bedroom or bathroom
You live in a multi-unit building and neighbouring units have also reported mice
You have been trapping for two weeks and the population has not declined

In those cases, the source of pressure is almost certainly the shared building system — a wall chase, the basement, a neighbouring unit — and trapping inside your apartment is treating a symptom, not the cause.

What Professional Exclusion Inside Walls Involves

A competent NYC exterminator will not just bait and leave. The standard professional approach involves:

Inspection of every pipe penetration, utility entry point, baseboard gap, and appliance cavity
Interior trapping with snap traps placed at identified run points, returned to weekly
Exclusion work — sealing every confirmed or suspected gap with gnaw-resistant materials (copper mesh, metal plates, hydraulic cement, not foam alone)
Chase assessment — identifying whether the building’s internal pipe chases are open and, if so, working with building management to address them

In a multi-unit building, your exterminator should communicate with building management. A landlord-engaged exterminator may be inspecting only your unit; push for a building-wide assessment if the problem is recurring.

When to Call a Pro

Call a licensed NYC exterminator immediately if:

You hear sounds in more than one wall location
You find evidence in rooms other than the kitchen
DIY trapping has not reduced activity after one week
You smell decomposition inside a wall (a sealed mouse, or a mouse that died from a trap you cannot access)

Under NYC law, residential landlords are responsible for pest-free conditions. Document everything — your reports to the super, the building’s treatment visits, and any ongoing evidence — in case you need to escalate to HPD via 311.

Mice in walls are a structural problem as much as a pest problem. Trapping alone buys time; exclusion ends it.

Mice in Walls: How to Get Rid of Them in NYC