Borers and fungal decay: telling them from termites
Australia's timber pest category has three members. Two of them get almost no attention, and one of those is entirely preventable.
Three pests, one inspection
A timber pest inspection to AS 4349.3 covers termites, wood-boring insects and fungal decay. Grouping them makes sense in practice: all three destroy structural timber, and all three favour the same damp, unventilated places. Biologically, though, they have nothing to do with each other. The response to each is different.
The three signatures
| Termites | Borers | Fungal decay | |
|---|---|---|---|
| Exit holes | None | Yes: clean and round | None |
| Inside the timber | Galleries lined and packed with mud | Tunnels with fine powdery frass | No tunnels at all |
| Texture | Hollow, surface intact | Sound apart from the tunnels | Soft, crumbling or cracking into cubes |
| Needs sustained moisture | Yes | Depends on species | Absolutely. It is the whole mechanism |
Mud and no holes means termites. Holes and powder, no mud means borers. Neither, but soft means decay.
Borers: the question is always active or old
Wood-boring beetles lay eggs on or in timber; the larvae tunnel inside, sometimes for years; the adults chew their way out. And those exit holes are what people notice. The powderpost group attacks the sapwood of certain hardwoods and produces a very fine, flour-like frass.
The critical distinction is whether the attack is current. Old flight holes in a hundred-year-old floor are extremely common and usually mean an infestation that finished decades ago. Indicators of an active attack are holes that look fresh and pale inside rather than dark and dusty, and clean frass appearing below the timber. Especially if it reappears after you have swept it away.
Borers are also mostly a sapwood problem, which is why they turn up in flooring, furniture and lining more than in structural members. And why they are usually a lesser problem than the noise they generate.
Fungal decay: not an insect at all
Decay is a fungus digesting the timber. It needs sustained moisture (timber kept dry does not rot, full stop) which makes it the most directly preventable of the three. Fix the water and you have fixed the cause; no product, no treatment.
Decayed timber loses strength well before it looks dramatic. It is typically soft, darker or oddly bleached, and either crumbles to a fibrous mass or cracks into a cube-like pattern across the grain. In a subfloor it turns up on bearer ends built into damp brickwork, on joists over poorly ventilated ground, and around anything that has been leaking.
Because the same conditions produce both, decay and termites are regularly found in the same subfloor. If you have one, look hard for the other. And either way the underlying question is the same: why is that timber wet?
Which of the three should worry you most
Termites, comfortably. They attack sound structural timber, they work concealed, and a colony can do serious damage in a period measured in months rather than decades. Borers are usually slower and usually in less critical timber. Decay is serious but announces its cause, and the cause is fixable.
What they share is the lesson: they all point at moisture and ventilation, and the inspection that finds one will find the others.
Frequently asked questions
How do I know if borer holes are old?
Old holes are dark and dusty inside; fresh ones look pale and clean. The stronger test is frass: sweep it away, and if a new pile appears below the timber, something is still emerging.
Can I treat fungal decay?
You fix the moisture, which stops the fungus, and then you deal with any timber that has lost strength. Treating the fungus while the timber stays wet does not solve anything.
Does a timber pest report cover all three?
Yes. AS 4349.3 covers termites, wood-boring insects and fungal decay, which is why the report is called a timber pest report rather than a termite report.
Sources
What this page explains is based on these official sources. If you check one and it does not match what you read here, send it to us and the article gets corrected.
- Department of Health, Victoria. Pest control — termites
- Standards Australia. Australian Standards (AS 3660 termite management, AS 4349.3 timber pest inspection)