Silverfish Killer Powders

Most work by physical action rather than by poisoning. They only work while dry, so a powder that gets damp, is walked in, or is vacuumed up stops working - keep treated areas dry and undisturbed and reapply after cleaning.

Into the gaps rather than across open floor: skirting joints, behind and under the bath and basin, around pipework where it enters a wall, inside airing cupboards, and along cracks in dark, damp corners. Apply a fine, barely visible layer - a thick deposit is more likely to be walked out of place than a light one.

Used correctly, food-grade diatomaceous earth can be suitable for homes with pets and children. Apply sparingly into cracks and crevices out of reach, avoid raising dust while applying, and keep it dry and undisturbed. Follow the label directions on the individual product.

After vacuuming, after cleaning, and any time the area has been dampened or disturbed. Powders are not used up as they work - they stop working once they are no longer dry and in place, so reapplying is about restoring the layer rather than topping up a dose.

Two different pictures. If the powder is dry and undisturbed but sightings continue, it is probably not deep enough into the harbourage - silverfish shelter in wall voids, under baths and behind tiles, so work it further into the gaps rather than spreading it more widely. If the treated area is a damp bathroom, the powder may not be staying dry enough to do anything, in which case a spray suits that room better.

A powder holds in cracks and crevices and keeps working as long as it stays dry, which suits airing cupboards, voids and dry gaps. A spray suits damp rooms where a powder will not stay dry, and gives faster knockdown on what you can see. In a bathroom, a spray usually does more.

Possibly, and it matters here more than most places. The common silverfish needs consistently humid conditions. Grey silverfish, sometimes called paperfish, tolerate much drier air, live longer and are spreading in UK buildings - which is the one situation where a powder in dry cracks suits them better than it suits common silverfish, since they will happily live in the dry gaps you are treating. If you have dried the room out and they are still there months later, this is the likely reason.

Silverfish need humidity, so they persist wherever they can find it. Fixing the leak, running the extractor, ventilating, and dealing with damp in cellars or behind cold walls does more than any treatment. Clearing out old paper and cardboard removes the food source. Our guide to getting rid of silverfish yourself covers it in full.

If numbers are still climbing after a full treatment cycle and you have already dealt with the damp, if they have spread through several rooms, or if they are getting into stored books, documents or archive material you cannot afford to lose. Look for a qualified pest controller with BPCA membership.