How do I get rid of silverfish?

Silverfish are one of the few household pests that are almost entirely a symptom rather than a problem. They cannot survive in a dry room, so a persistent infestation is telling you something about the building rather than about the cleaning.

Safety

Step by step

1. Confirm what you are dealing with.Small, wingless, silver-grey, teardrop-shaped, with three tail filaments and a fish-like wriggling movement. Fast, and they run from light. Firebrats look similar but prefer heat rather than damp.
2. Treat it as a damp problem.They need relative humidity above roughly 75% and die below it. Nothing you spray will hold if the room stays damp, and nothing needs spraying if it dries out.
3. Find where the moisture comes from.Bathrooms and kitchens without adequate extraction, a leaking pipe under a sink, a cold external wall, an unventilated cupboard, or a suspended floor with blocked air bricks. That is the actual repair.
4. Ventilate properly.Run extractor fans for twenty minutes after showering and cooking, open windows wide and briefly rather than on the latch, and keep trickle vents open. This alone resolves many cases.
5. Use a dehumidifier where airing is not enough.A cellar, a bathroom with no window, or a persistently damp room. Getting the humidity below about 50% makes the environment uninhabitable for them.
6. Remove what they eat.Starches and cellulose — cardboard boxes, old newspapers, paper bags, wallpaper paste, book bindings, and stored natural fabrics. Cardboard storage in a damp cupboard is both food and shelter.
7. Move stored paper into plastic.Anything kept in a loft, cellar or under the stairs. Sealed plastic boxes remove both the food source and the harbourage, and protect what is inside.
8. Seal the gaps they live in.Cracks around skirting, gaps behind bath panels, holes where pipes enter, and the space behind kitchen units. Filler or sealant removes the daytime hiding places.
9. Use sticky traps to map them.Placed against skirting and in corners, they tell you where the activity actually is, which is usually not where you saw one. That points at the moisture source.
10. Use diatomaceous earth in voids.A fine mineral dust that damages their exoskeleton. Puffed into cracks, under bath panels and behind units — not spread across surfaces, and not where it will be inhaled. It only works dry.
11. Do not rely on sprays.A contact spray kills what it touches and does nothing about the population living in the wall void. It is the least effective response and it is the one most people reach for first.
12. Expect it to take weeks.They are long-lived and slow-breeding, so numbers fall gradually rather than suddenly. Judge it over a month, and by whether the humidity has actually changed.
13. Get advice if there is no obvious damp.A large persistent population in a room that seems dry suggests moisture somewhere you cannot see — a slow leak, a failed damp course, or a cold void. That is worth investigating properly.

Tips

• A cheap hygrometer in the affected room is more useful than any treatment. It tells you whether you have actually changed the conditions.
• They are attracted to the bath and basin because they cannot climb the smooth sides — one in the bath means they are in the room, not that they came up the drain.
• Books and photographs stored in a damp room are what they will damage. Move those first, before doing anything else.

Common mistakes

• Spraying insecticide and doing nothing about the damp — The environment that supports them is unchanged, so the population rebuilds from the voids within weeks. Humidity is the control, not the spray.
• Assuming it means the house is dirty — They live on starch and cellulose in damp conditions, not on food debris. A spotless damp bathroom supports them perfectly well.

If it doesn't work

Questions people ask