Silverfish in London Homes: Why They Thrive and How to Clear Them

Silverfish are one of the most common — and most ignored — pests in London. They don't bite, they don't spread disease, and they rarely cause a panic. But in damp Victorian and Edwardian properties, particularly those with cellars, basements or poorly ventilated bathrooms, they can establish large, long-lived populations that quietly damage books, wallpaper, clothing and even plaster.

The good news is they're one of the easiest pests to control once you understand what they need: moisture, darkness and starchy food. Remove the moisture and you remove the problem.

What silverfish actually look like

Adult silverfish (Lepisma saccharina) are 10–12 mm long, silvery-grey, and move with a distinctive fish-like wiggle. They have two long antennae and three tail-like appendages at the rear. Younger specimens are smaller and paler.

They are nocturnal and extremely fast when disturbed — the flash of movement you see out the corner of your eye in a bathroom at night. They prefer temperatures between 22–27°C but can survive colder conditions if the humidity is high enough.

Where they live in a typical London property

Silverfish are strongly attracted to moisture and darkness. In London's older housing stock they are found in very predictable spots.

• Bathrooms — behind the bath panel, under sinks, inside vanity units, around extractor fans that don't vent properly.
• Basements and cellars — particularly those with stone walls, poor drainage, or rising damp.
• Kitchens — under the sink, behind dishwashers, inside larders with condensation issues.
• Lofts — where a leaking roof or failed tank creates humid conditions.
• Behind bookshelves and inside cardboard boxes — the glue in bindings and the starch in paper are a food source.

The damage most people don't notice

Silverfish don't cause structural damage, but the cumulative effect on personal belongings can be surprisingly costly.

• Books and photographs — they eat the sizing and starch in paper, leaving notched edges, yellow stains and pages that fall out.
• Clothing — natural fibres like cotton, linen, silk and wool are all on the menu. Damage usually appears as irregular holes or thinning.
• Wallpaper — they feed on the paste, leaving peeled edges and small scrapes across the surface.
• Plaster and filler — in very damp conditions they will nibble on dried plaster and filler compounds.

The only long-term fix: reduce humidity

Chemical treatments for silverfish are secondary. The primary control is environmental — drop the humidity below 50% relative humidity and silverfish cannot survive or breed.

• Fix leaking pipes, dripping taps and failed grout — even small continuous leaks create enough moisture.
• Improve ventilation — run extractor fans for 15 minutes after every shower or bath; upgrade to a humidity-triggered model if yours is manual.
• Use a dehumidifier in basements and cellars during autumn and winter — aim for 45–50% RH.
• Move stored items off cold external walls where condensation forms.
• Increase airflow behind furniture — even 5 cm of clearance makes a difference.

When to call a pest controller

If you've fixed the moisture issue and still see silverfish after 4–6 weeks, a professional can apply a residual insecticide to harbourages and advise on any hidden damp problems you've missed. Typical London pricing for a silverfish treatment is £90–£180 for a 2–3 bedroom property, often combined with a wider insect survey.

Frequently asked questions

Are silverfish harmful to humans?

No. They don't bite, sting, carry disease, or trigger allergies in most people. The damage is limited to belongings — books, clothing, and wallpaper.

Will they go away on their own in winter?

Not in a heated London property. Central heating keeps them active year-round. In unheated outbuildings they may slow down, but they don't die off.

Do silverfish traps work?

Sticky traps catch some adults and help monitor numbers, but they don't address the underlying moisture issue or the eggs hidden in cracks. Use them as a diagnostic tool, not a fix.