What are mice in walls doing at night?

Mice are primarily nocturnal. The sounds you hear at night are mice actively foraging for food (traveling from wall voids into kitchen and pantry areas), gnawing on materials inside the wall to maintain their nests or expand access routes, and movement between nesting areas. Mice can travel 10 to 30 feet from their nest during a single foraging trip. The scratching and gnawing sounds typically intensify after midnight when building activity is lowest.

How do I get mice out of wall voids in my NYC apartment?

Professional treatment combining interior bait stations, trapping along travel routes, and exclusion of entry points is the most effective approach for wall void infestations in NYC apartments. DIY snap trap placement along baseboards helps but only captures mice during foraging — it does not address the nest inside the wall. Contact your building management if you are a tenant, as NYC landlords are legally required to address rodent infestations under the NYC Housing Maintenance Code.

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

With professional treatment, most wall void infestations show significant reduction within 7 to 14 days as trapping and bait takes effect. Complete elimination typically requires 3 to 6 weeks and at least 2 to 3 follow-up service visits. Infestations that have been active for months and involve large populations may take longer. Thorough exclusion of all entry points is the key factor determining whether the infestation stays resolved or recurs.

Can mice in walls cause damage in NYC apartments?

Yes. Mice gnaw constantly and will chew through electrical wiring (a significant fire hazard), insulation, structural wood, and pipes inside wall voids. Gnawed wiring is estimated to be a contributing factor in a meaningful percentage of residential fires annually. Mice also contaminate wall insulation with urine and droppings. The damage inside wall voids is often not visible until significant harm has already occurred, which is why early treatment is important.

Mice in Walls: How to Know and What to Do in NYC

Scratching and rustling inside walls at night usually means mice. Learn how to confirm mouse activity in wall voids, why NYC apartments are especially vulnerable, and what professional extermination involves.

The rustling, scratching, or gnawing sounds inside your walls at night are among the most common rodent complaints in New York City. Unlike a mouse running across the floor — visible and undeniable — mice in wall voids are easier to dismiss or misidentify. But the sounds are a reliable indicator of active mouse activity, and the longer it continues without treatment, the larger the infestation grows.

How to Confirm Mice Are in Your Walls

Wall sounds alone are not definitive — pipes, insects, and building settling can produce similar noises. Confirm mouse activity with secondary evidence:

Droppings: Mouse droppings are 1/8 to 1/4 inch long, dark brown to black, and pointed at both ends. Find them along wall edges, in cabinet corners, behind appliances, and wherever mice travel. Fresh droppings are dark and moist; older droppings are gray and crumble when touched.
Gnaw marks: Mice gnaw constantly to keep their incisors trimmed. Look for gnaw marks on wood trim, baseboards, food packaging, cardboard boxes, and cabinet corners. Fresh gnaw marks are light-colored; older ones are darker.
Grease marks: Mice travel the same paths repeatedly and leave grease smears from their fur along baseboards, pipes, and wall edges where they squeeze through gaps. Dark smudge marks along wall-floor junctions indicate regular mouse traffic.
Nesting material: Mice shred soft material for nesting — insulation, paper, fabric, and cardboard. Finding shredded material in drawers, inside appliances, or in storage areas indicates a nearby nest.

Why NYC Apartments Are Especially Vulnerable

New York City housing creates conditions uniquely favorable to mice inside wall voids. Pre-war apartment buildings in Manhattan, Brooklyn, and the Bronx feature extensive pipe chases, hollow walls with deteriorated plaster, and gaps around old steam radiator risers that provide access between floors and units. A single entry point at the building foundation can connect through wall voids to apartments on the third or fourth floor.

Modern construction is more airtight, but NYC building density means mice enter from adjacent structures, subway infrastructure, and the street — all connecting to the building envelope at multiple points. High-rise buildings present particular challenges because entry points at the roof level (HVAC equipment, parapet gaps) allow mice to move downward through wall voids.

Where Mice Enter Wall Voids

To get into walls, mice first enter the building through these typical access points:

Gaps where utility pipes (gas, water, electrical conduit) penetrate the foundation or exterior walls
Gaps at the junction of the building slab and exterior wall, especially where the slab has cracked or settled
Floor drain surrounds in basement and mechanical areas
Behind washing machine and dishwasher connections where drain lines exit through walls
Around abandoned pipe penetrations that were never properly sealed
Door and window frames where caulking has deteriorated in older buildings

Once inside, mice travel through wall voids via gaps around pipes, holes between apartments, and unsealed conduit penetrations. A single 1/4-inch gap is large enough for a young mouse to squeeze through.

What Professional Treatment Involves

Treating mice in wall voids requires a different approach than treating surface mouse activity. Simply placing snap traps along baseboards addresses mice that leave the wall for food but does not address the population inside the void.

Professional treatment for mice in walls typically involves:

Inspection and mapping: The technician identifies infestation scope, locates likely entry points, and determines which walls have the most activity.
Interior bait placements: Tamper-resistant bait stations placed at floor level adjacent to active wall segments. Where code allows, bait may be introduced into accessible wall voids through access points.
Trapping program: Snap traps placed along active travel routes reduce the population within 7 to 14 days. Behind refrigerators, under sinks, and along walls adjacent to known nesting sites are prioritized.
Exclusion: Sealing entry points is the single most important long-term step. Without exclusion, new mice will continue entering. Exclusion materials include copper mesh, steel wool, hardware cloth, and professional-grade sealants.
Follow-up: A single treatment rarely eliminates a wall void infestation. Follow-up visits at 1 to 2 week intervals to check traps, replenish bait, and assess progress are standard.

Can You Handle It Yourself?

DIY approaches can reduce surface mouse activity but typically cannot fully address a wall void infestation. Snap traps along baseboards capture foraging mice but do not reach the nest inside the wall. Ultrasonic repellers have no reliable evidence of effectiveness against established infestations. Over-the-counter rodenticide bait placed in wall voids without tamper-resistant stations creates risks for pets and can result in mice dying inaccessibly inside walls — causing odor, staining, and potential health issues.

Control Exterminating has treated rodent infestations in NYC wall voids since 1973. Call (212) 696-4164 to schedule an inspection.