Woodlice 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 - which matters with woodlice, since the places they gather are damp by definition.

Into dry cracks and gaps on the routes in: along skirting, at door thresholds, around air bricks, where pipes enter walls, and behind appliances. Apply a fine, barely visible layer. Avoid applying it in visibly wet areas, where it stops working almost immediately - treat the dry approach rather than the damp patch itself.

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 on the individual product.

After vacuuming, after cleaning, and any time the treated area has been dampened. Powders are not used up as they work - they stop working once they are no longer dry and in place.

Two different pictures. If the powder is damp or has been walked through, it has stopped working and the location is wrong for a powder - move it to a dry approach, or use a spray instead. If the powder is dry and undisturbed but woodlice keep appearing, they are coming in by a route you have not treated: check air brick surrounds, the base of external doors, and cracked render.

Often not. Woodlice do not bite, damage sound timber or carry disease - they need damp and feed on decaying plant matter. A few near a door usually means a gap and some moisture rather than an infestation, and sealing and drying does more than treating. For a cluster already indoors, vacuuming them up and emptying the vacuum outside is quicker than any treatment. Treat where numbers are persistent, or where they are getting well inside.

Woodlice come indoors for shelter as outdoor conditions turn cold and wet, so autumn and winter is when most people notice them, and heavy rain pushes a wave in at any time. It is the weather rather than a failed treatment, and numbers usually fall away again in spring.

Closing the routes in and taking away the damp. Seal gaps at door thresholds, air bricks and pipe entries, improve ventilation in cellars and utility rooms, and move compost, leaf litter, log piles and pots away from the base of the wall outside. Check the gutters and downpipes as well - a blocked gutter or leaking downpipe soaks the wall beneath it, and that wet strip at the base of the wall is where woodlice gather before coming in. Read our guide to getting rid of woodlice yourself for the full picture.

If woodlice keep appearing in numbers well inside the house rather than near doors and air bricks, the underlying problem is damp rather than pests, and a damp or timber specialist will usually be more use than a pest controller. If you do want pest control as well, look for a qualified pest controller with BPCA membership.