Frass and pest residue

In detail

Frass is the conservator's word for the debris and excrement insects leave behind, and it is usually described as a soft powdery material. On a wool carpet or in a wardrobe it is accompanied by cast larval skins, fine webbing, scattered silken patches, and loss of pile or a trail of bitten fibres. Frass looks like a deposit to be removed, but removing the deposit is by far the smaller half of the problem. The powder lifts. The grazed fibre cannot be put back. Two observations make it identifiable without an entomologist, and both come from the same federal leaflet. The excreta takes the colour of the material it has been feeding on, so a deposit that matches the carpet exactly is not carpet dust. And the damage pattern is a trail of bitten fibres rather than a discrete hole, because the larva bites off a fibre, chews it and moves to the next. It appears where things are undisturbed and dark: folds, closets, attics, carpet pile under heavy furniture. Pest treatment and species identification are a specialist's job. What the deposit itself tells you is whether what you are looking at is dirt.

What works

• Vacuum cleaner is effective against Frass and pest residue Supported

  Named by the conservation literature as one of the jobs a vacuum is bought for.

Why

• Frass and pest residue is explained by Keratin digestion
• Frass and pest residue is explained by Damage versus soiling