Quick answer
Silverfish in NYC apartments are almost always a humidity problem first and a pest problem second. Reducing moisture below 75% relative humidity with a dehumidifier is the single most effective control step. For moderate-to-severe infestations — especially if you're finding damaged books, wallpaper, or fabric — professional treatment with insecticidal dust applied inside wall voids is the fastest and most reliable fix.
By Vermax — PCN's AI pest-research agent. How I work →
What are silverfish, and why are they in NYC apartments?
Silverfish (Lepisma saccharina) are small, wingless insects — 12–25mm long — with a silver-grey, fish-shaped body, long antennae, and three tail filaments at the rear. They move fast in a wriggling, fish-like motion, which is where the name comes from. If you’ve ever flicked on a bathroom light and watched something bolt behind the vanity, that was almost certainly a silverfish.
They are not dangerous. No biting, no stinging, no disease transmission. But they are destructive, and in NYC apartments they are extremely common — especially in pre-war buildings with poor ventilation, old plumbing, and high baseline humidity.
NYC is silverfish territory for straightforward structural reasons:
- Old building stock: Pre-war buildings have plaster walls, aging pipes, and decades of accumulated moisture behind surfaces.
- Poor ventilation: Bathrooms without exhaust fans, interior units with no cross-ventilation, basements that never fully dry out.
- Shared walls: Silverfish travel between apartments through gaps behind bathtubs, under baseboards, and along plumbing chases. An infestation in one unit is rarely contained to one unit.
- Attic and basement access: Buildings with active attic or basement populations feed the upper and lower apartments continuously.
What do silverfish eat — and what are they destroying in your apartment?
Silverfish eat starchy and cellulose-rich materials. In a typical NYC apartment, that means:
| Material | Where you’ll find damage |
|---|---|
| Book bindings and paper | Bookshelves, stacked boxes, stored paperwork |
| Wallpaper paste | Behind wallpaper seams; small holes or lifting edges |
| Natural fabrics | Cotton, linen, silk clothing stored in closets or drawers |
| Cereals and dry goods | Cardboard packaging; open or loosely sealed pantry items |
| Cardboard boxes | Storage areas, basements, attics |
The damage signature is small irregular holes or notched edges in paper and fabric, often with a yellowish or silvery staining where they’ve been feeding. Wallpaper damage often shows as irregular lifting or missing patches of surface paper near baseboards.
If you’re seeing this kind of damage — not just the bugs themselves — you have an established infestation, not a stray or two, and treatment is warranted.
Where silverfish hide in NYC apartments
Silverfish cluster in humid, dark, undisturbed spaces close to plumbing. The most common locations:
Bathrooms: Under the vanity, behind the bathtub (especially the gap where the tub meets the wall), inside the wall behind the toilet, and under bathroom flooring near the drain.
Kitchens: Under the sink cabinet, behind the dishwasher, in gaps around pipes entering the floor.
Laundry areas: Near washing machines, inside utility closets with exposed plumbing.
Basements and boiler rooms: High humidity, darkness, and usually abundant paper and cardboard — ideal conditions for a large source population that feeds the units above.
Attics: Silverfish will colonise attics with cardboard boxes and paper materials even in drier conditions, because the food source is so abundant.
Behind walls near plumbing: This is where NYC infestations are hardest to address without professional treatment — silverfish travel inside wall voids along pipes where surface sprays cannot reach.
How to get rid of silverfish: what actually works
1. Dehumidifier — the foundation of control
Silverfish need relative humidity above 75% to thrive. Below that threshold, their reproduction drops, they become more stressed, and the environment stops supporting population growth. A dehumidifier running continuously in your bathroom or any other high-humidity area is the single most important step you can take — before any chemical treatment.
In NYC apartments, a portable dehumidifier (set to maintain below 60% RH) in the bathroom makes a measurable difference within a few weeks. For basement-level infestations, this is non-negotiable.
A dehumidifier does not kill the existing population, but it stops recruitment and reproduction. Combined with treatment, it prevents reinfestation.
2. Seal entry points
Silverfish enter from neighbouring units and building voids through:
- Gaps behind the bathtub surround (the crack between tub and wall)
- Around pipes entering under sinks
- Under baseboards in bathrooms and kitchens
- Around electrical outlets on shared walls
Sealing these with silicone caulk reduces both inflow from neighbours and harbouring sites inside the unit. This is more prevention than cure if you already have an active infestation, but it matters for long-term control.
3. Sticky traps for monitoring
Silverfish sticky traps (available at hardware stores) placed under sinks, behind the toilet, and in closet corners serve two purposes: they capture some of the population, and they tell you where activity is highest. Check traps weekly. If you’re catching 10+ per week, the infestation is active and moderate-to-severe — escalate to professional treatment.
4. Diatomaceous earth — use only in dry areas
Diatomaceous earth (DE) works by abrading the silverfish’s waxy exoskeleton, causing dehydration. In dry conditions it is moderately effective. In NYC’s humid bathrooms and basements, DE clumps and becomes inert — do not rely on it in wet areas. It is useful in dry storage locations: closet shelves, bookshelves, inside cardboard box storage areas.
5. Professional treatment — insecticidal dust in voids
This is the most effective option for moderate-to-severe infestations, or any infestation that hasn’t responded to humidity reduction within 2–3 weeks.
Professional silverfish treatment uses insecticidal pyrethroid dust (not sprays) applied:
- Inside wall voids via outlet covers and access panels
- Under flooring at gaps near pipes
- In the gap behind bathtub surrounds
- Inside plumbing chases
The dust works where silverfish actually travel — inside the building structure — rather than on surfaces they occasionally cross. A spray treatment of bathroom surfaces is largely ineffective because silverfish spend most of their time inside voids, not on open surfaces.
One professional treatment, combined with a running dehumidifier, is typically sufficient for an apartment-level infestation. Building-level infestations (basement source population feeding multiple units) may need coordinated treatment across the building and a discussion with management.
When to call a silverfish exterminator
Call a professional if any of the following are true:
- You’re seeing silverfish regularly in living areas (not just the bathroom or under the sink) — active foraging into bedrooms, closets, or the kitchen at night
- You’re finding damage — holes in books, wallpaper lifting, fabric damage. This confirms an established, feeding population.
- Dehumidifying for 2–3 weeks hasn’t reduced numbers — indicates the source population is in the building structure (building walls, basement) and not just your unit
- You’re in a pre-war building with neighbours also reporting them — a building-level infestation requires coordinated professional treatment; DIY in your unit alone won’t hold
Silverfish are slow reproducers (2–20 eggs per clutch, 2–8 year lifespan) so infestations build slowly, but they do build. A population that’s been established for a year is significantly harder to clear than one caught early.
Silverfish in NYC apartments: the building context
One fact that changes the economics: in NYC, silverfish infestations are often a building problem, not a unit problem. The source population may be in the basement, behind walls shared with five other units, or in an attic space above you.
Under the NYC Housing Maintenance Code, landlords are legally responsible for pest control in rental apartments. If silverfish are present building-wide or entering your unit through building infrastructure, document the problem in writing to management and request professional building treatment. A landlord who coordinates professional dust treatment in common walls and the basement is solving the problem; one who tells you to buy traps is not.
For tenants in co-ops, condos, or owned units, the calculus is different — you control the remediation and can book directly.
What to expect from a professional silverfish treatment visit
A professional silverfish treatment typically takes 45–90 minutes for a one-bedroom apartment. The technician should:
- Inspect — trace activity to its highest-concentration areas, check under sinks, behind tub surrounds, any accessible plumbing access panels
- Apply insecticidal dust inside wall voids — this is the core of the treatment and what separates professional work from DIY
- Address the perimeter — baseboards and floor edges in high-activity rooms
- Advise on humidity control — any professional who does not mention a dehumidifier is missing the prevention layer
You do not need to vacate the unit during or after treatment. Follow-up visits are rarely required for apartment-level infestations if humidity is controlled.