Termites in wood: what the galleries inside actually tell you
The outside of a termite-damaged board rarely shows much. Open it up, or one already has been, and the galleries inside are where the real evidence lives.
The tap test tells you damage exists. It does not tell you why
A hollow sound or a screwdriver that sinks in with no resistance means something has been eating the timber. It does not say what, and treating every hollow board as identical wastes the one piece of evidence you actually have: the shape of the galleries inside it. Once a board is opened, whether by an inspector, a tradesperson mid-repair. Or damage that has already broken through, that internal structure is worth reading before it gets thrown out.
Mud-packed galleries running with the grain
Subterranean termites, the group behind most serious Australian structural damage, need a humid, sheltered environment and cannot tolerate open air for long. Their galleries inside timber usually carry a thin lining of soil-coloured material. It is a mix of mud, saliva and faecal matter that keeps the workings sealed off from the dry air of the room.
The tunnels tend to follow the softer spring-growth layers along the grain. That is why a badly affected board can look almost hollow along its length while the surface stays intact.
Finding that mud lining inside a broken timber is a strong pointer to the subterranean genera (Coptotermes, Schedorhinotermes, Nasutitermes). It is also why cutting a route back to that gallery can lead, eventually, to a concealed nest under a slab, in a stump or inside a nearby tree.
Clean galleries, and pellets that are not on the floor
Drywood termites work differently, and it shows in the wood. Because the whole colony lives inside the timber and never needs ground contact, there is no mud to carry in and no reason to line the tunnels.
What you find instead are smooth, clean-walled galleries that cross the grain as often as they run with it, together with small kick holes where pellets have been pushed out. What frass rules out covers those pellets in detail. The point that belongs here is that clean, ungritty galleries with no soil lining are the opposite signature to a subterranean find, not a milder version of it.
Frass, sawdust or nothing: three different insects
A tunnel packed with fine, powdery frass that spills out on contact usually points away from termites altogether and towards a wood borer. And the two most common offenders behave differently again: a powderpost beetle's frass runs out like flour, while a furniture beetle's is grittier, with visible pellets mixed through it. Neither leaves mud. A gallery with no frass at all and no lining, in timber that is also visibly wet or fungal-stained, is more often decay than any insect.
| What you find inside the wood | Points to |
|---|---|
| Mud-coloured lining, tunnels following the grain | Subterranean termites |
| Clean, smooth tunnels crossing the grain, kick holes | Drywood termites |
| Fine, flour-like frass with no mud | Powderpost beetle |
| Gritty frass with visible pellets, no mud | Furniture beetle |
| Soft, stained timber, no galleries or frass at all | Fungal decay, not an insect |
This narrows the group. It does not identify the species
Everything above is a pointer, and a useful one, but it stops short of a determination. Species identification is made from a soldier under magnification, not from the pattern of a gallery, and getting the genus wrong changes which treatment strategy actually makes sense. What the galleries do let you do is describe what you found accurately to whoever inspects it, which is worth more than a guess.
If the timber is already broken open, resist the urge to keep breaking it apart to see how far the damage runs. Photograph it, leave it as it is, and book an inspection to AS 4349.3. Breaking open more galleries, or the boards themselves, risks losing insects that would have helped the identification. If the colony is still active nearby, it also gives the termites reason to seal off and re-enter somewhere you are not watching.
What none of this replaces
A cross-section of one board is one data point on one piece of timber. It says nothing about how far the colony has spread through the rest of the building, whether a barrier is still doing its job. Or whether the nest is metres away or on the neighbouring block. Only a licensed technician working through the whole structure, not one board, answers that.
Frequently asked questions
How can I tell if it is termites just from the damaged wood?
The pattern inside the timber is a real clue. A mud-coloured lining running with the grain points to subterranean termites, while clean, smooth tunnels crossing the grain with no mud point to drywood termites. Neither confirms a species; that is done from a soldier under magnification.
Why does mud inside the wood matter so much?
Subterranean termites need a humid, sheltered environment and cannot survive long in open air, so they line their galleries with a mud-like mix to seal the workings off. Finding that lining is one of the clearest pointers to the subterranean group, which is also the group responsible for most Australian structural damage.
Is sawdust coming out of a hole always termites?
No. Termites do not typically leave loose sawdust or frass outside the timber, since subterranean species stay sealed inside their mud-lined galleries. Fine, flour-like material spilling from a hole more often points to a wood borer such as a powderpost or furniture beetle.
Should I keep breaking the wood open to see how far it goes?
No. Beyond the first check, further breaking risks destroying the evidence an inspector needs and, if a termite colony is still active, disturbing it in a way that makes it abandon the route and re-enter somewhere concealed. Photograph what you have found, leave it, and book an inspection.
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)