Silverfish vs grey silverfish: how to tell the difference

Silverfish and grey silverfish look similar enough to be confused constantly — but they behave very differently, and knowing which one you have tells you how urgent the problem is.

The quick test

Why the difference matters

Common silverfish are mostly a nuisance and a signal that you have a humidity problem. Fix the damp and their numbers usually fall on their own.

Grey silverfish are a genuine pest. They digest cellulose, so they feed on paper, cardboard, book bindings and wallpaper — and they can damage documents, photographs and stored belongings. They breed faster, live longer, and spread through a building rather than staying in one damp room.

Where each one comes from

• Common silverfish are usually already in the building, drawn out by moisture
• Grey silverfish almost always arrive from outside — carried in inside cardboard boxes, packaging, furniture or moving crates

This is why new-build homes and recently renovated flats see them so often — and why the problem has nothing whatsoever to do with how clean your home is.

The good news: the same traps work on both

Both species climb the rough outer wall of a pitfall trap, drop into a catch cup holding an oil-based attractant, and cannot get out. No chemicals, safe with children and pets — and the catch cup tells you which species you are dealing with. Check the size and tail length of what you find.

Frequently asked questions