Woodworm vs Wet Rot: What Is the Difference?

Wet rot and woodworm can both make timber feel soft, look dark and behave structurally unsound — but they are different problems that need different solutions. Treating one when you have the other wastes money and time while the real issue continues unchecked.

What is wet rot?

Wet rot is caused by several species of fungi — most commonly Coniophora puteana (cellar fungus) — that break down and digest timber when it is consistently wet. Unlike dry rot (Serpula lacrymans), wet rot requires sustained high moisture — typically above 50% wood moisture content — and is confined to the wet area. It does not spread through masonry.

Wet rot is far more common than dry rot. It appears wherever timber is repeatedly soaked: external joinery (window sills, frames, door bottoms), joist ends in damp sub-floor voids, and timber in contact with leaking plumbing.

What is woodworm?

Woodworm is the larva of wood-boring beetles — most commonly the common furniture beetle, which needs timber at a more modest moisture level (12–18%) to sustain an infestation. Woodworm causes damage through boring tunnels, leaving exit holes and frass as the visible evidence.

Key differences

Feature	Woodworm	Wet rot
Cause	Wood-boring beetle larvae	Fungal decay (Coniophora and others)
Exit holes?	Yes — round, 1–2mm	No
Bore dust?	Yes — pale, powdery	No
Timber colour	Usually unchanged or slightly darkened	Darkens significantly — deep brown to black
Timber cracking	Tunnels along the grain	Longitudinal cracking following the grain
Smell	None	Musty, damp odour
Moisture needed	12–18%	50%+
Confined to wet area?	Not strictly — can spread	Yes — does not spread beyond wet zone

How to tell them apart

Wet rot indicators:

• Timber that is visibly darkened — deep brown, grey or black
• Soft, spongy feel that worsens toward the centre of the affected area
• Cracking following the grain — longitudinal splits, not cuboidal (cuboidal cracking suggests dry rot)
• No exit holes, no frass
• Musty damp smell
• Often concentrated at a single wet point — a joist end, a window sill bottom, an area below a leaking pipe

Woodworm indicators:

• Round exit holes (1–2mm for furniture beetle)
• Pale bore dust beneath holes
• Softening concentrated at sapwood layers, not uniformly through the timber
• Adult beetles visible May–September
• No characteristic smell

Can they occur together?

Yes. Wood-boring weevil (Euophryum confine) is a species that specifically targets already-damp, decaying timber. Finding wood-boring weevil is often a secondary symptom of wet rot — the weevil is not the primary problem.

Where timber is maintained at the elevated moisture levels that sustain wet rot, furniture beetle infestations also tend to be more aggressive and persistent. Sub-floor voids with blocked ventilation may show both wet rot in joist ends against damp masonry and furniture beetle galleries in the drier spans of the same joists.

Why the damp matters more than the treatment

Both wet rot and woodworm associated with damp will recur if the moisture source is not addressed:

• Wet rot treated with fungicide but without fixing the leaking roof or rising damp will return within months
• Woodworm treated with permethrin in a sub-floor void with blocked airbricks will face re-infestation as the elevated moisture conditions remain attractive to adult beetles

For wet rot: The correct sequence is: find and fix the moisture source → cut out and replace affected timber → treat surrounding timber and any adjacent masonry with fungicidal solution → improve ventilation.

For woodworm with associated damp: Treat the active infestation → address the source of elevated moisture → improve sub-floor ventilation → monitor for re-infestation over two to three seasons.

What to do next

If your timber shows softening, darkening or structural deterioration and you are unsure whether you are looking at woodworm, wet rot or both, a professional timber survey will give you a clear diagnosis. Our dry rot and damp treatment service covers both fungal decay and the underlying moisture problems that cause it.

Read more: Woodworm vs dry rot · Signs of woodworm · Is woodworm dangerous?