Silverfish
Common silverfish are about 10 to 12 mm long, carrot-shaped and covered in silvery scales, with long antennae and three tail bristles. They move with a wriggling, fish-like motion. They need humidity, so they live in bathrooms, kitchens, basements and under sinks, coming out at night.
Grey silverfish (paper fish)
The grey silverfish, Ctenolepisma longicaudatum, is larger, up to around 18 mm, greyer and hairier. Unlike common silverfish, it can survive in drier conditions and is found throughout homes, including bedrooms and living rooms. It has spread quickly in the UK in recent years and is common in new-build flats, where it is thought to arrive in building materials and cardboard packaging.
Do they cause damage?
Silverfish feed on starch, sugars, mould, paper, glue, book bindings, wallpaper paste and dust. They can damage books, documents, photos and wallpaper, but they do not bite, sting or spread disease.
How to reduce silverfish
- Reduce humidity: use extractor fans, open windows after bathing, fix leaks and dry wet areas
- Seal gaps along skirting boards, around pipes and at the edges of bath panels and tiles
- Vacuum regularly, including along skirting and in corners
- Store books, papers and photos in sealed plastic boxes rather than cardboard
- Get rid of old cardboard boxes, which grey silverfish love
Professional treatment
For grey silverfish or persistent infestations, a professional treatment combining bait and residual insecticide in cracks, skirting and voids works over several weeks. See silverfish control.
Questions and answers
Are silverfish a sign of damp?
Common silverfish usually indicate high humidity. Grey silverfish can live in drier homes.
Can silverfish come up through drains?
Not usually. They hide in cracks and gaps near pipes and under baths rather than coming up the drain.
Why do I have silverfish in a new flat?
Grey silverfish often arrive in building materials and packaging during construction or a move.
Related pages
This page is general information, last reviewed on 19 October 2026. It is not a substitute for an on-site inspection.