Timber Borers: Holes, Frass and How They Differ From Termites

A small round hole in a floorboard, a neat cone of pale dust beneath it, and an immediate assumption that termites have arrived. It is one of the most common misdiagnoses in timber pest work, and the difference matters: borers and termites need different treatments, different urgency and different insurance conversations.

This guide explains which borers actually matter in a home, what the evidence looks like, and how to decide whether you are looking at an active problem or an old one.

The four borers you are likely to hear about

• Lyctus, or powderpost beetle. Attacks the sapwood of starch-rich hardwoods such as oak, ash, walnut, meranti and some eucalypts. Adults are slender and brown, and they do re-infest seasoned timber, which is what makes this species significant. Exit holes are around 1.5 to 2 millimetres and the frass is fine and flour-like.
• Anobium, or furniture beetle. Attacks softwoods and older furniture, joinery and framing, but needs higher moisture content to thrive. Exit holes are similar in size and the frass is slightly gritty. The life cycle is slow, often a year or more.
• Longicorn borer. Attacks freshly felled or unseasoned timber. Larvae are large and galleries are wide; holes are oval and noticeably bigger. It generally does not re-infest dry structural timber in a house.
• Ambrosia or pinhole beetles. Attack green timber and leave small dark-stained holes. They do not re-infest dry, seasoned wood.

There is one more worth knowing about. The European house borer is a serious pest of pine framing and roof timbers, established in parts of Western Australia and subject to national surveillance. It is not established in this region, but any unusual borer activity in pine framing is worth reporting rather than dismissing.

What the evidence looks like

• Small round or oval exit holes, one to three millimetres across, in floorboards, joists, bearers, architraves or furniture.
• Frass — fine powder, or slightly gritty pellets — directly beneath the holes or caught in a nearby cobweb. Fresh frass is the key sign of activity.
• Hollow-sounding timber when tapped, with crumbling edges around old holes.
• Dead beetles on windowsills in spring and summer, particularly near timber floors or furniture.
• Tunnels and galleries visible in a cross-section of broken timber, filled with dust rather than soil.
• Weakened surface fibres around the holes, so the timber feels rough or friable.

A useful test: sweep the frass away, mark the area and check again in a few weeks. New powder means active larvae. No new powder over a season usually means the infestation is historic.

How borers differ from termites

This is the distinction that decides everything.

• Frass. Borers push powdery frass out of the timber. Termites digest the timber and leave no powder; they build mud tubes and galleries lined with soil and faecal material.
• Where the damage is. Borers work near the surface and exit outward. Termites hollow timber from the inside, often leaving a thin skin of paint or timber with nothing behind it.
• Moisture and contact. Subterranean termites usually need ground contact or a moisture bridge. Borers need moisture in the timber itself but not soil contact.
• The insect. Borers are beetles with hard wing cases. Termites are soft-bodied, pale and ant-like, and are almost never seen in the open.
• Treatment. Termites require colony elimination, baiting or a chemical or physical barrier. Borers require species identification, moisture correction and sometimes surface or injected treatment, or replacement of affected timber.

If you are unsure, do not treat. An inspection that identifies the insect costs far less than a barrier applied to a borer problem, or the reverse.

Why moisture is the real driver

Both Lyctus and Anobium need moisture in the timber, and most significant borer activity in a house traces back to a damp environment.

• Blocked or buried subfloor vents, which leave the underfloor humid and still.
• A leaking shower, tap or waste pipe wetting floor timbers.
• Gutters overflowing onto fascia and eaves.
• Soil or landscaping built up above the damp course.
• A concrete path or deck holding moisture against the wall.
• A subfloor with no cross-flow ventilation after an extension or renovation.

Correcting moisture does not kill existing larvae, but it removes the conditions that let an infestation persist and spread. It is also cheaper than repeated treatment.

Which timber is at risk

• Hardwood floorboards, parquetry and joinery. Risk depends on species and how much sapwood is present. Lyctus needs starch, and the heartwood of most durable hardwoods is not susceptible.
• Softwood framing, bearers and joists. Vulnerable to Anobium where moisture is high, particularly in older homes with poor subfloor ventilation.
• Furniture, antiques and imported pieces. A common entry route for powderpost and furniture beetle, and worth inspecting before purchase.
• Timber offcuts and stored material under the house or in a shed, which can act as a reservoir.

What treatment involves

Treatment is decided by species, timber type and whether the timber is structural.

• Identification first. Exit hole size, frass texture and timber type usually identify the species. This determines whether treatment is needed at all.
• Activity assessment. Fresh frass, light-coloured wood inside the holes and recent exit holes indicate active larvae. Old, dusty holes with no frass often need monitoring rather than treatment.
• Surface residual treatment for accessible decorative timber, floorboards and joinery, applied to the timber surface and around holes and edges.
• Borate treatment for structural timber in subfloors and roof voids, where penetration into the timber is needed.
• Injection into galleries in some situations, particularly joinery and furniture where the item is worth conserving.
• Replacement where structural timber has lost section, where the infestation is advanced, or where the timber is not economic to treat.
• Moisture correction, without which treatment rarely holds.
• A follow-up inspection at around 12 months, because borer life cycles run a year or longer and new exit holes are the proof of success or failure.

Furniture, antiques and second-hand timber

A chest of drawers or a dining table with borer holes is a decision, not an emergency. Small, isolated pieces can often be treated and kept, particularly where the damage is old and confined. Pieces with active frass, soft edges or structural movement are usually not worth the risk of bringing home.

If you collect, buy from dealers who will confirm treatment history, inspect seams, undersides and drawer backs, and quarantine new pieces in a dry garage for a few weeks while you watch for fresh frass.

Borers and a pre-purchase inspection

A building and timber pest inspection under AS 4349.3 reports on termites, borers and wood decay. That is different from a termite-only inspection, and different again from a termite barrier quote.

If you are buying an older home with hardwood floors, a subfloor and a suspended timber frame, the timber pest report is where borer findings should appear. Read the section on borers specifically, and ask whether the inspector considered the activity current or historic.

What not to do

• Do not spray a general household insecticide onto timber and assume the job is done. It does not penetrate galleries.
• Do not seal or paint over exit holes before treatment, which traps the evidence and can trap larvae in the timber.
• Do not confuse borers with termites and buy a termite barrier you do not need, or ignore termites because you assumed borers.
• Do not ignore a borer infestation in a damp subfloor. Moisture plus active larvae is the combination that causes structural loss.

Reading a timber pest report

Reports vary in usefulness, and a few phrases are worth understanding.

• "Active" means the inspector found fresh frass, recent exit holes or live insects. It warrants treatment or replacement.
• "Inactive" or "historic" means old damage with no current evidence. Monitoring is usually the right response, not a rushed spray.
• "Borer damage noted, species not determined" is an incomplete finding. Ask which species, and what the recommendation is based on.
• "Areas not inspected" matters. Subfloors with limited access, boxed-in areas and concealed timbers are common gaps, and they are exactly where structural damage hides.
• Photographs should show the holes, the frass and the timber type. A written note without a photo is hard to act on months later.

If a report recommends treatment without identifying the species, the recommendation is guesswork. Identification is what separates a harmless historical hole from an active infestation in structural timber.

What borer activity looks like across a year

Borers work slowly, which makes a single inspection a snapshot rather than a verdict.

• Spring to early summer. Adults emerge, leaving fresh exit holes and frass. Dead beetles appear on windowsills. This is the easiest time to confirm activity.
• Summer. Mating and egg laying on suitable timber. Females seek out moisture and exposed sapwood.
• Autumn and winter. Larvae tunnel and feed, often with little visible sign from the outside. Frass may stop appearing altogether.

That is why a twelve-month follow-up matters. A treated area with no new frass through a full emergence season is a genuine result; a treated area checked two weeks later tells you nothing.

Borers, building reports and a sale

If you are selling, a borer finding in a building report usually prompts a buyer question rather than a deal-breaker. What helps is evidence: species identification, an assessment of whether the activity is current, and a treatment record if work has been done.

If you are buying, ask whether the report distinguishes borers from termites, whether the affected timber is structural, and whether the recommendation is treatment or replacement. Sellers sometimes hold a termite barrier certificate that says nothing about borers, and buyers sometimes assume it does.

For older homes with hardwood floors, a subfloor and a suspended frame, a timber pest inspection under AS 4349.3 is the document that answers these questions. A termite-only inspection will not.

What changes the price of a borer treatment

• The species involved, which decides whether treatment is necessary at all.
• Whether the affected timber is structural or decorative.
• Access to the subfloor, roof void and the affected floor area.
• Whether galleries need injection rather than surface treatment.
• Whether timber replacement is required, which brings carpentry into the quote.
• The follow-up inspection, which is part of confirming success rather than an optional extra.

Ask what the follow-up includes. A borer job without one is an application, not a result.

Borers and termite protection are different contracts

One of the most common misunderstandings in timber pest work is assuming a termite barrier protects the whole building against insects that eat wood. It does not.

• A termite barrier is designed and certified to deter or detect subterranean termites, under Australian Standard 3660.
• Borers live inside the timber itself and are unaffected by a barrier in the soil or a physical sheet under the slab.
• A borer treatment does nothing to prevent termites, and a termite certificate says nothing about borers.

Both matter, and both need to be addressed separately. If you have a termite barrier and a borer problem, you have a borer problem that the barrier was never intended to solve.

A word on treated and resistant timber

Borate-treated timber resists borer attack, and durable heartwood of resistant species is naturally less susceptible. Neither is a licence to ignore moisture, which drives both borer activity and decay.

Where replacement is part of a treatment, ask what species or treatment is being used and why. Replacing susceptible sapwood with the same product invites the same result.

How Accurate Pest Control can assist

We identify the borer species, assess whether the timber is structural, treat what is active and advise when replacement is the better answer.

• Timber borers — species, signs and treatment detail
• Termite inspections — the other timber pest, and why it is different
• Pre-purchase inspections — AS 4349.3 timber pest reports
• Get a free quote