Lyctus brunneus
Powderpost Beetle
Lyctus brunneus — a hardwood specialist that reduces the sapwood of oak, ash and walnut to powder as fine as flour. Often found in newer hardwood flooring and recently imported or seasoned timber.
- Very fine, flour-like frass — the key identifier
- Small 1–2mm round exit holes in hardwood sapwood
- Common in new hardwood floors and imported timber
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What it is
The hardwood beetle that makes flour
The powderpost beetle (Lyctus brunneus) gets its name from the spectacularly fine bore dust it produces — powder so soft and floury that it gives the species away long before you spot a beetle. It is a small reddish-brown insect, around 5mm long, and unlike most of the woodworm British homeowners worry about, it has very particular tastes: it attacks only the sapwood of certain hardwoods.
Those hardwoods are the wide-pored, starch-rich species — oak, ash, walnut, elm and many tropical timbers. The female lays her eggs into the open pores of the sapwood, and the larvae feed on the starch stored there, eventually tunnelling the wood into a mass of fine powder behind a sound-looking surface. Because it depends on starch that is highest in young, recently converted timber, the powderpost beetle is most often a pest of newer hardwood rather than ancient structural oak.
How to identify it
Four signs of powderpost beetle
The holes look like ordinary woodworm, so identification comes down to the powder and the timber. Rub the dust between your fingers — if it feels like flour, think powderpost.
Very fine, flour-like frass
The clearest sign. Powderpost frass is as soft as talc or plain flour — it sifts through your fingers without any grittiness, quite unlike the sandy bore dust of furniture beetle.
Small round holes, 1–2mm
Neat, round exit holes the same size as the common furniture beetle's. On their own the holes are easy to confuse — it is the powder that distinguishes this species.
Hardwoods only
Lyctus attacks the sapwood of wide-pored hardwoods such as oak, ash, walnut, elm and tropical timbers. It never touches softwood, so its presence in a pine joist effectively rules it out.
Newer or imported timber
Often found in recently installed hardwood flooring, furniture and joinery, or in freshly seasoned and imported stock — rather than in centuries-old structural oak.
Where you will find it
New floors, joinery and imported timber
The powderpost beetle behaves very differently from the woodworm most people picture in an old loft. It is a pest of relatively young hardwood, so the classic places to find it are recently fitted oak or ash flooring, new hardwood furniture, joinery, panelling and stair parts — and timber that has recently been imported or freshly seasoned.
The reason is the beetle's life cycle. Eggs are frequently laid while timber is still in the timber yard, the workshop or in transit, before it is ever installed in a home. The larvae then develop quietly inside the wood, and the first you know of it is fine powder appearing months — sometimes a year or two — after a new floor was laid or a piece of furniture arrived. That delayed emergence is why a brand-new hardwood floor can, frustratingly, start producing dust.
It is worth keeping a sense of proportion. The powderpost beetle attacks sapwood only, and as hardwood matures and its starch content falls, it becomes far less susceptible. The damage is real and should be treated, but it is usually confined to the sapwood portions of newer hardwood rather than threatening the structural heartwood of a building.
Life cycle
How the Powderpost Beetle develops
Eggs laid in cracks
Larvae tunnel (3-4 yrs)
Pupation near surface
Adult exits leaving holes
Treatment & prevention
How to treat it — and keep it out
Treating powderpost beetle starts with confirming it. The fine flour-like frass is a strong clue, but a professional survey establishes the species for certain, checks whether the attack is still active, and identifies which timbers are affected. Getting this right matters, because the treatment and the timber involved are different from a typical softwood woodworm job.
For active infestations in accessible hardwood, the standard approach is a surface application of insecticidal spray — a water-based product that kills emerging adults and treats the surface of the sapwood. Where flooring, furniture or joinery is heavily damaged, replacing the affected sapwood-rich sections can be the cleaner long-term answer than repeated treatment. Our full woodworm treatment service covers both, with a written quote and guarantee.
Prevention: seasoning and moisture control
Because the powderpost beetle depends on starch-rich, damp sapwood, prevention is genuinely effective. Three measures make the biggest difference:
- Proper seasoning. Use well-seasoned, kiln-dried hardwood from reputable suppliers; properly dried timber carries far less of the moisture and starch the beetle needs.
- Moisture control. Keep indoor humidity and timber moisture content low with good ventilation and heating — dry hardwood is a poor host for Lyctus.
- Seal exposed surfaces. Varnishing, sealing or finishing bare hardwood closes the open pores the female needs to lay her eggs in.
For background on safe, approved treatment products, the HSE — biocides & pesticide safety is the official reference, and the Property Care Association sets the standards we work to.
Related guides & services
Insecticidal Spray Treatment
Water-based permethrin spray — the standard professional treatment for active beetle in accessible timber.
Learn more →Woodworm Treatment
Surveyed, guaranteed eradication of wood-boring beetle for homes and commercial property.
Learn more →Common Furniture Beetle
The UK's most common woodworm — the species powderpost beetle is most often mistaken for.
Learn more →Signs of Woodworm
Exit holes, frass and weak timber — how to read the clues and tell active from historic.
Learn more →Frequently asked questions
How is the powderpost beetle different from common woodworm?
Why does it turn up in new hardwood floors and furniture?
How do you treat powderpost beetle?
Can I prevent it?
Fine powder in your hardwood? Let's check it.
If a new oak floor or piece of furniture is shedding flour-like dust, book a free survey. We will confirm the species, treat active infestation and advise on prevention — with a 30-year guarantee on treated timber.
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