The essentials in 30 seconds
The common silverfish (Lepisma saccharina) is about 1 to 2 cm long, teardrop-shaped, silver-grey, with long antennae and three thin tails. It lives in damp, dark places and feeds on starch, paper, glue, food crumbs and dust. To get rid of it: lower the humidity, clean and vacuum skirting boards and cupboards, seal cracks and gaps around pipes, and use sticky traps to see where they gather. Expect results within two to three weeks; if traps keep filling after that, look for a leak or hidden damp.
- Silverfish do not bite or sting, but they damage paper, books, photos and starched fabrics.
- Damp is the main cause: common silverfish struggle to survive in dry homes.
- Larger, greyer silverfish in dry rooms may be grey silverfish, which need a different approach.
What silverfish are and what they look like
They are primitive wingless insects that move with a wriggling, fish-like motion, hence the name. They are nocturnal and avoid light, which is why you see them when you switch on the bathroom light at night or move a box in the loft. They scrape at surfaces rather than chew, because their mouthparts are very weak.
| Insect | Appearance | Where it appears |
|---|---|---|
| Silverfish | Silver-grey, teardrop shape, three tails, 1–2 cm | Bathrooms, kitchens, cellars, cupboards, books |
| Grey silverfish (long-tailed silverfish) | Larger, 15–20 mm, blotchy grey scales, a fringe of bristles, antennae and tails longer than the body | Any room, including dry living rooms and bedrooms |
| Firebrat | Similar shape, mottled grey or brown | Very warm spots: near boilers, ovens and hot pipes |
| Woodlouse | Grey, armoured, often rolls into a ball | Patios, plant pots, under doors |
| Young cockroach | Brown, long legs and antennae, runs fast | Kitchens, behind appliances |
| Fact | Figure |
|---|---|
| Lifespan | About 3 years for silverfish, 2 for firebrats |
| Eggs | Clutches average about 50 eggs |
| Hatching | 19 to 32 days for silverfish; about 14 days for firebrats |
| Without food | Several months |
| Preferred conditions | 22 to 32 °C; above that they need relative humidity over 75 % |
| Firebrats | Prefer very warm spots, above 32 °C, and tolerate humidity as low as 30 % |
What causes silverfish and where they come from
- High humidity: bathrooms without a window, long showers without an extractor fan, laundry dried indoors.
- Leaks or condensation: behind bathroom units, under the sink, in cold corners where condensation forms.
- Cracks and gaps: loose skirting boards, open tile joints, gaps around pipes.
- Food: paper, cardboard, books, wallpaper paste, flour, cereals, pet food and dust.
- Cardboard boxes stored for a long time in lofts, cellars or wardrobes.
If they suddenly appear somewhere new, check for a leak or a patch of damp in the wall nearby.
| Where you see them | Likely cause | What to do |
|---|---|---|
| Bath, basin or shower tray at night | Damp bathroom; they wander in at night and struggle on the smooth sides | Extractor fan after every shower, seal tile joints and the bath edge |
| Under the kitchen sink | A slow drip or a damp cupboard base | Check the trap and hoses; dry and ventilate the cupboard |
| Among books, papers and boxes | Food source and hiding place | Move papers into sealed plastic boxes; vacuum shelves |
| Near the boiler or hot pipes | Firebrats | Seal gaps around pipes; keep the area clean and dusted |
| Dry living rooms and bedrooms, larger grey insects | Grey silverfish | Sticky traps to confirm, then professional advice |
| Cold external walls with mould | Condensation | See our guides to black mould and condensation |
How to get rid of silverfish: a two-week plan
-
01
Day 1: measure the humidity
A cheap hygrometer shows the relative humidity. Aim to keep rooms at around 50–60 %; constantly damp rooms suit silverfish.
-
02
Day 1: set sticky traps
Place them in corners and along walls where you see silverfish. Number them and note the catches every couple of days.
-
03
Days 1 to 3: ventilate and dehumidify
Open a window or run the extractor fan after showers, and use a dehumidifier in the dampest rooms.
-
04
Days 2 to 4: fix leaks
Check traps under sinks, flexible hoses, the base of the toilet and shower seals. A constant drip keeps the area damp.
-
05
Days 3 to 5: vacuum thoroughly
Skirting boards, inside wardrobes, shelves and behind furniture. Empty the bag or canister outside.
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06
Days 3 to 5: clear paper and cardboard
Store documents and books in sealed plastic boxes, keep dry food in airtight tubs and clear out old boxes.
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07
Week 2: seal cracks
Fill open joints, gaps behind skirting boards and around pipes with silicone or filler.
-
08
Days 14 to 21: compare the traps
Catches should be falling. If traps still fill up, there is an untreated source of damp or hiding place nearby.
Grey silverfish: the larger species in dry rooms
The grey silverfish (Ctenolepisma longicaudata), also called the long-tailed silverfish, is a larger species recently found in the UK and common in many European countries. Its damage is similar to that of the common silverfish, but it can breed and cause damage at lower humidity, so it turns up in heated, dry rooms where drying the air alone has less effect.
- Confirm it with sticky traps: grey silverfish are bigger, greyer and bristlier than the common species.
- Keep the basics going: vacuuming, sealing gaps and storing paper in plastic boxes still help.
- Ask a pest control professional for an inspection if catches stay high after two or three weeks.
What silverfish damage
Silverfish do not bite and are not known to spread disease. They scrape and eat paper, photos, book bindings, labels, wallpaper and starched fabrics such as cotton and linen, leaving irregular holes, thinned patches and yellowish marks. They particularly like coatings of starch or gelatine, so old photos, flock wallpaper and wallpaper paste are favourites.
How to protect books and documents:
- Keep them in rooms with steady, moderate humidity, away from external walls.
- Store papers, photos and keepsakes in sealed plastic boxes rather than cardboard.
- Dust shelves and vacuum behind books a couple of times a year.
- Check stored boxes in the loft or cellar every few months.
When to call a pest control company
- They appear in several rooms even after you have reduced the damp.
- Books, documents or valuable collections are being damaged.
- You suspect grey silverfish in dry rooms.
- You suspect structural damp (rising damp, leaks) that needs a diagnosis.
- You live in a block of flats and they come from shared ducts or risers.
Silverfish: frequently asked questions
Do silverfish bite?
No. Their mouthparts are too weak: they scrape at paper and fabric instead. They do not sting either.
Are silverfish harmful?
They are harmless to people and pets. They can damage paper, books and starched fabrics, and they point to high humidity.
What causes silverfish?
Damp, darkness and food: paper, glue, starch, crumbs and dust. Unventilated bathrooms, leaks and stored cardboard boxes are the usual triggers.
Where do silverfish come from?
They live in cracks, behind skirting boards and in boxes, and often arrive in stored cardboard, books or furniture. They multiply where the room stays damp.
What kills silverfish?
Drying the room is the main fix. Sticky traps catch them, and silica gel or diatomaceous earth dusts work in dry voids.
Why are they in my bath or sink?
Bathrooms are the dampest room in the house. Silverfish wander in at night looking for moisture and struggle to climb back up the smooth sides.
What are grey silverfish?
A larger, greyer species, recently found in the UK, that can breed at lower humidity than the common silverfish. If you find them in dry rooms, get a professional inspection.
Does a silverfish mean I have cockroaches?
No. They are different insects, although both like damp, hidden corners.
Sources
Official and heritage guidance, checked on 26 October 2026.
- University of California IPM · Silverfish and firebrats ↗Identification, lifespan, eggs, temperature and humidity needs, damage, dusts, baits and management.
- English Heritage · Silverfish and grey silverfish, pest fact file 8 ↗Sizes, signs of damage, the role of damp and grey silverfish breeding at lower humidity.
- US EPA · Dos and don'ts of pest control ↗Safe use of insecticides at home.
- WHO · Guidelines for indoor air quality: dampness and mould ↗Health effects of damp indoors.
Still seeing them after airing the room?
Measure the humidity for a week and note which rooms they appear in before you ask for help.