Fresh deposits matter more than old residue
A small clean pile appearing below a flight hole is more useful than dust trapped on a beam for years. Mark or clean a small area and see whether new material appears.
Not all frass looks like flour
Different beetles leave different debris. Some is very fine; some contains distinct pellets. Correct species identification should use the hole shape, timber type, frass and adult insect where available.
Building vibration can release old material
Floor work, hammering or even repeated movement can shake historic frass out of old galleries. One fresh-looking pile therefore needs to be considered with other evidence.
Photograph it before cleaning
A close photograph with a scale, together with a wider view of the timber, can be useful if the material is later assessed by a specialist.
Useful technical sources
- Historic England — Timber Treatments and Pest Control
- Historic England — Timber Decay in Buildings and its Treatment
These links provide background guidance. A particular building still needs its own inspection.