Spider Killer Powders

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

Worth asking before you treat. A glass and a piece of card will move most house spiders outside in a few seconds, and released well away from the wall they rarely walk straight back in - our guide to keeping spiders out of your home starts there. A powder earns its place in dry gaps and edges you cannot keep revisiting - loft eaves, garage skirtings, behind fixed furniture - rather than as a first response to seeing one in the bath.

Into the gaps and along the edges spiders travel: skirting joints, corners, around window and door frames, air brick surrounds, and in lofts, cellars and garages. Apply a fine, barely visible layer rather than a thick deposit, which is more likely to be walked out of place.

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 area has been dampened or disturbed. A powder is not used up as it works - it stops working once it is no longer dry and in place.

Remove it rather than dusting around it. A single sac can hold up to a few hundred eggs and they usually hatch within two to three weeks. Vacuum it up with the web, then empty the vacuum straight into an outside bin rather than leaving the bag or canister indoors. Sacs get missed in ceiling corners, behind and under furniture, inside window reveals, and in the undisturbed parts of lofts, cellars and garages - the same places a powder is most useful afterwards.

A powder holds in dry gaps and edges and keeps working while dry, which suits lofts, garages and behind furniture. A spray gives faster knockdown and suits frames and corners you can treat directly. Sticky traps catch what is walking and show you the routes. For most homes, traps plus proofing does more than any of them alone.

If the sightings are in autumn, that is seasonal - mature males wander looking for females for a few weeks and no treatment changes it much. If it is year-round, spiders are staying because there is prey, so reducing flies and other insects indoors does more than treating the spiders. Also check the powder is dry and actually on the routes they walk rather than in the middle of a floor.

Proofing and prey. Seal gaps around frames, air bricks, vents and pipe entries, fit brush strips to doors, clear webs as they appear, and cut back planting touching the walls. Then reduce the insects they are feeding on. Our guide to getting rid of spiders yourself works through it.

Rarely necessary for spiders. Consider it if activity is heavy and persistent year-round in a commercial or food setting, if you cannot find or reach where they are getting in, or if someone has had an unusual reaction to a bite. Look for a qualified pest controller with BPCA membership.