What is that silver bug in my house?

How to identify a silverfish

Silverfish are flat, carrot-shaped insects with no wings, two long feelers at the front and three tail bristles at the back. They move in a fast, wriggling way, which is where the name comes from.

The common silverfish is about 10 to 12 mm long and silvery-blue. The grey silverfish (long-tailed silverfish, *Ctenolepisma longicaudatum*) is a little larger, uniformly grey, with longer feelers and tail bristles. It was first recorded in Britain in 2014 in Reading, and a published study counted 49 UK cases by early 2021, including the first in Scotland. It is now widespread in homes.

Lookalikes

• Booklice are 1 to 2 mm, pale and soft, and live on mould. See our booklice page.
• Carpet beetle larvae can look like silverfish: the Natural History Museum says two-spot carpet beetle larvae are torpedo-shaped. They are hairy and slower. See carpet beetles.
• Earwig nymphs are pale but have tiny pincers rather than three tail bristles.

Why they are in your home, and are they harmful?

Common silverfish like warm, damp, dark places. BPCA notes they forage at night in bathrooms, kitchens and pantries, and by day hide behind skirting boards, wallpaper and bath panels. They cannot easily climb smooth surfaces, so one trapped in the bath or sink is typical.

The grey silverfish is different. Research says it tolerates low humidity, survives long periods without food, and lives only in buildings, often in dry living areas, upstairs and among cardboard and paper.

Silverfish do not bite, sting or spread disease. They eat starchy material, so they can nibble book bindings, wallpaper paste, photographs and some fabrics. Damage is usually minor.

How to get rid of them

For common silverfish, fix the damp. Ventilate bathrooms, repair leaks, and use a dehumidifier in persistently damp rooms. Seal gaps around pipes and skirting, and vacuum cracks.

Cut down their food: store paper, photographs and spare linen in sealed plastic boxes rather than cardboard, and clear piles of old paper. Sticky traps help you see where they travel.

Grey silverfish are harder. Research found that ordinary silverfish treatments often fail against them, and that baits containing indoxacarb gave a strong reduction in a field test. Check the label of any product you buy and use it as directed.

When a professional is worth it

Common silverfish in a damp bathroom rarely need one: dry the room out and they fade. A professional is worth considering if you have grey silverfish across several rooms, if they are damaging items you value, or if you run a home archive or collection. Ask what they will treat with and for a follow-up visit, because one treatment seldom clears a bait-led problem.