What Causes Silverfish? Signs, Risks and Prevention

What causes silverfish is usually a combination of suitable shelter, available food and, for common silverfish, persistently humid conditions. They often appear in bathrooms, kitchens, utility rooms, cellars and other quiet spaces where moisture collects and materials containing starch or cellulose are available.

Finding one silverfish does not automatically mean your home is dirty or seriously damp. However, repeated sightings can indicate excess humidity, a hidden leak or an established population living in cracks, wall voids or beneath flooring.

Identifying what is supporting the insects is more effective than simply killing the ones you see.

What are silverfish?

Silverfish are small, wingless insects with tapered bodies, silver-grey scales, long antennae and three bristles at the rear. Adults are commonly around 10 to 15 mm long, excluding their antennae and tail bristles.

They move quickly and usually retreat into cracks when disturbed. Their fish-like movement and reflective scales give them their common name.

Silverfish are generally active at night. During the day, they remain concealed in places such as:

• Gaps beneath skirting boards

• Cracks around pipes

• Floor and wall voids

• Cupboards

• Loose wallpaper

• Cardboard storage boxes

• Beneath baths and shower trays

• Behind kitchen units

• Cellars and basements

• Loft storage

They do not fly, bite or live on people or pets.

What causes silverfish in a home?

Silverfish do not appear spontaneously. Adult insects, young silverfish or eggs must first be introduced or gain access to the property. Once present, they can survive and breed if conditions are suitable.

The main contributing factors are moisture, shelter, food and time.

High humidity

Common silverfish favour humid environments. Bathrooms and utility rooms often provide moisture from bathing, drying clothes, condensation and limited ventilation.

A persistently humid microclimate can also develop behind units, beneath floors or inside a poorly ventilated cupboard even when the room itself feels dry.

Humidity is therefore a useful clue, but it should not be treated as proof of a major building defect.

Leaks and damp materials

A slow leak beneath a bath, behind a toilet or under a kitchen unit can create suitable conditions without producing an obvious pool of water.

Other possible sources include:

• Leaking waste pipes

• Defective seals around baths and showers

• Condensation on cold pipes

• Water entering around windows

• Damp plaster or timber

• Poorly ventilated cellars

• Wet materials after a flood

• Laundry drying indoors without enough ventilation

If silverfish repeatedly appear in one small area, inspect that location for a local moisture source.

Food materials

Silverfish can feed on materials containing starches, sugars and cellulose. Potential food sources in a property include:

• Paper and cardboard

• Wallpaper paste

• Book bindings

• Labels and photographs

• Some natural textiles

• Microscopic mould

• Food crumbs and residues

• Dust and organic debris

• Starchy adhesives

They can survive for extended periods with limited food, so ordinary cleaning alone may not eliminate an established population.

Dark, undisturbed shelter

Silverfish avoid light and disturbance. Cracks, stored boxes, floor voids and spaces behind fitted furniture provide protected harbourage.

A spare room full of cardboard boxes may therefore support activity even when it is not visibly damp. Bathrooms can provide humidity while nearby cupboards provide shelter and food.

Warm indoor temperatures

Stable indoor temperatures allow silverfish to remain active for more of the year. Warmth alone does not cause an infestation, but it can support development when food and moisture are also available.

Items brought into the property

Silverfish or their eggs may occasionally be introduced in:

• Cardboard packaging

• Stored books and papers

• Second-hand furniture

• Archive boxes

• Materials moved from damp storage

• Items transferred between flats or commercial premises

An introduced insect will not necessarily establish an infestation. Conditions within the new property must still support its survival and reproduction.

Why do silverfish appear in bathrooms?

Bathrooms provide several features silverfish favour: moisture, warmth, darkness and numerous gaps around services.

You may see one trapped in a bath or basin because the smooth surface prevents it from climbing out. This does not mean it came through the plughole. It may have fallen from a wall, pipe boxing or the edge of the fitting.

Common bathroom harbourages include:

• Gaps around pipe penetrations

• Spaces beneath a bath

• Loose flooring edges

• Cracks behind tiles

• Damaged sealant

• Ventilation ducts

• Cupboards containing paper products

• Voids behind plasterboard

Repeated sightings justify checking for leaks and ventilation problems, particularly when mould, peeling paint or persistent condensation is also present.

Improving ventilation may make conditions less favourable, but it will not immediately remove insects or eggs hidden inside the structure.

Why are silverfish in a bedroom or living room?

Silverfish are associated with bathrooms, but they are not restricted to wet rooms.

They may appear in bedrooms, living rooms or home offices where there are:

• Books and paper

• Wallpaper and adhesives

• Cardboard storage

• Natural fabrics

• Undisturbed floor edges

• Damp external walls

• Condensation behind furniture

• Routes from an adjoining bathroom or pipe void

A bedroom sighting does not necessarily mean that the whole room is excessively damp. The insect may be travelling from a nearby void.

Grey silverfish can also tolerate drier conditions than common silverfish. This related species has become increasingly relevant in the UK and may be found away from obviously humid rooms.

Are silverfish a sign of damp?

Silverfish can be an indicator of humid or damp conditions, but they are not a diagnosis.

Common silverfish need damp conditions for successful egg laying and development. Regular sightings can therefore justify investigating:

• Hidden plumbing leaks

• Poor extractor performance

• Persistent condensation

• Defective seals

• Damp beneath flooring

• Water ingress

• Inadequate subfloor ventilation

However, a single insect may have wandered from another part of the building or arrived with stored items.

Grey silverfish complicate the picture because they can breed and cause damage at lower humidity than common silverfish. Correct identification matters before assuming that the property has a damp problem.

If the building has visible mould, staining, damaged plaster or a persistent musty smell, investigate the moisture issue on its own merits rather than relying on silverfish as the only evidence.

Are silverfish a sign of a dirty house?

No. Silverfish can occur in clean and well-maintained properties.

Clutter, dust and stored cardboard can provide more food and shelter, but poor hygiene is not the only cause. A hidden leak, structural void or humid bathroom can support silverfish in an otherwise spotless home.

Cleaning remains useful because it removes food debris, exposes harbourages and makes activity easier to monitor. It should form part of a wider plan rather than being presented as a judgement on the household.

Are silverfish harmful?

Silverfish are not known for biting people or transmitting disease in the way that some other pests can. Their main significance is the damage they may cause to vulnerable materials and the possibility that they indicate a moisture problem.

They may damage:

• Books and documents

• Wallpaper

• Photographs and labels

• Cardboard packaging

• Some textiles

• Stored collections

• Materials coated with starch, gelatine or organic adhesives

Damage can appear as surface grazing, irregular holes, thinning or yellow staining.

The risk is greater where important papers, archives, collections or delicate materials are stored for long periods. English Heritage notes that common silverfish can damage paper, books, prints, photographs, labels and wallpaper, particularly under humid conditions.

Silverfish are not necessarily responsible for every hole found in fabric or paper. Carpet beetles, moth larvae, booklice and other insects produce different patterns of damage. Identification should be based on the insect and the evidence, not the damage alone.

Does seeing one silverfish mean an infestation?

Not always.

One silverfish may be an isolated insect, particularly if it was found near an external door, packaging or items recently brought into the property.

An established problem is more likely when:

• Silverfish are seen repeatedly

• Insects of different sizes are present

• Sightings occur in several rooms

• Several insects scatter when an item is moved

• Paper or wallpaper shows compatible damage

• Shed scales or droppings are found

• Monitoring traps repeatedly catch insects

• Activity continues after moisture has been reduced

Silverfish hide well, so the number seen in the open may not reflect the total population. At the same time, it is unhelpful to assume that one sighting means hundreds are concealed in the walls.

Monitor the area and look for a pattern.

How to find where silverfish are coming from

Begin with the room where activity is most frequent.

Inspect:

• Pipe entries

• Skirting board gaps

• Loose wallpaper

• Cracks around flooring

• Spaces beneath sinks

• Bath and shower panels

• Cupboards containing paper

• Cardboard boxes

• Damp external walls

• Areas behind appliances

• Window reveals

• Ventilation grilles

Small insect-monitoring traps can help identify active routes. Position them along edges and near suspected harbourages rather than in the centre of a room.

Record where and when insects are found. This can reveal whether activity is concentrated around one leak or distributed through a shared structural void.

In flats and commercial buildings, silverfish may travel between units through service ducts, risers and wall voids. Treating one room without considering the wider route may provide only temporary improvement.

How to stop silverfish

Effective silverfish control combines environmental correction, physical management and targeted treatment where needed.

What causes silverfish to keep returning?

Silverfish are likely to return when the underlying moisture, harbourage or access route remains unchanged.

The following measures can make a property less suitable.

Reduce excess humidity

Use extractor fans during bathing and cooking, and allow them to run long enough to remove residual moisture. Open windows where safe and appropriate.

A dehumidifier may help manage humidity, but it should not be used to disguise an unresolved leak or building defect.

Repair leaks

Inspect seals, traps, waste pipes and supply connections. Pay attention to staining, swollen materials and musty smells beneath units.

Repairing the source is more important than repeatedly drying the visible surface.

Manage condensation

Heat and ventilate rooms appropriately. Avoid placing large furniture tightly against cold external walls where condensation can form unseen.

Persistent condensation may require broader building or ventilation advice.

Remove unnecessary harbourage

Reduce long-term cardboard storage, particularly in bathrooms, cellars and against outside walls. Store important documents in clean, dry containers.

Vacuum cracks and edges carefully to remove debris, shed scales and possible food material. Dispose of the vacuum contents outside.

Seal appropriate gaps

After checking for leaks and confirming that services do not require access, seal avoidable cracks around skirting boards, pipes and fitted units.

Sealing can reduce movement, but it will not resolve insects already established inside a void.

Protect vulnerable materials

Move books, papers, photographs and textiles away from damp walls and floors. Important collections may need specialist environmental and conservation advice.

Do home remedies get rid of silverfish?

Many suggested remedies rely on strong smells or substances that dry insects out. They may affect individual silverfish, but they rarely resolve eggs and insects hidden within wall or floor voids.

Common limitations include:

• The product does not reach the harbourage

• The underlying damp remains

• The treatment is removed during cleaning

• Dusts are applied where children or pets can contact them

• Repellents move insects without eliminating them

• The wrong pest has been identified

Avoid mixing household chemicals or applying unapproved substances as pesticides.

If using a product sold for insect control, confirm that silverfish and the intended location are covered by the label. Follow all application, ventilation and exclusion instructions.

When is professional silverfish control needed?

Professional help is reasonable when:

• Sightings continue despite reducing humidity

• Silverfish appear in several rooms

• A large number is found

• Important papers, books or textiles are at risk

• Activity occurs in a commercial property

• You cannot locate the source

• The infestation may extend between flats or units

• The affected area is inaccessible

• Previous treatments have failed

• You are unsure whether the insect is a common or grey silverfish

A professional inspection should identify the insect, locate the main activity and consider environmental conditions before recommending treatment.

GEM Services provides professional silverfish control for homes and businesses across Kent. Our fully insured team is based in Ashford and offers fast, discreet appointments, with same-day availability where possible.

Treatment may include targeted application to cracks, voids and harbourages together with practical advice on moisture, storage and proofing. We explain what is appropriate for the property and provide honest advice without pressure.

If you are unsure whether you have silverfish, carpet beetles or moths, compare the available evidence with our carpet beetle control and moth control information.

Call 07400 372204 or request a callback.

Frequently asked questions

What causes silverfish to suddenly appear?

A sudden increase in sightings may follow warm, humid weather, a leak, building work or disturbance of an established harbourage. It can also occur when several young insects reach a more visible stage.

Why do I have silverfish when my house is dry?

Humidity may be higher inside a hidden void than in the room. Alternatively, the insect may be a grey silverfish, which can tolerate drier conditions, or it may have travelled from elsewhere.

Do silverfish come through drains?

Silverfish may be found in sinks and baths because they fall in and cannot climb the smooth sides. Their presence does not prove they travelled through the drain.

Can silverfish climb walls?

Yes. They can move across many textured surfaces and may travel along walls, pipework and structural gaps. Smooth baths and basins can trap them.

Do silverfish bite?

Silverfish are not known for biting people. Their primary impact is damage to paper, wallpaper and other starchy materials.

Will silverfish go away if the room is dried out?

Reducing humidity can make conditions less suitable and disrupt breeding, but existing insects may survive for some time or move to another harbourage. Other control measures may still be necessary.

Are silverfish dangerous to pets?

Silverfish are not generally considered a direct threat to cats or dogs. Keep pets away from monitoring traps and insect-control products, and follow every product label.

Can silverfish damage clothes?

They may damage some fabrics, particularly materials containing starch, food residues or certain natural fibres. Clothes moths and carpet beetles are more common causes of significant textile damage, so correct identification is important.

How long do silverfish live?

Their development and lifespan depend on temperature, humidity and nutrition. An indoor population can persist for a long time when conditions remain favourable, which is why correcting the environment matters.

Should I be worried about one silverfish?

One sighting is a reason to inspect and monitor, not panic. Repeated sightings, different-sized insects or compatible damage provide stronger evidence of an established infestation.