Signs of borer in your timber

Frass is the thing that matters

Holes tell you borer were there at some point. Frass tells you they're there now - and that's the distinction that decides whether you need to do anything.

It looks like very fine sawdust with a yellow or orange cast, and it feels slightly gritty rubbed between your fingers. You'll find it in small piles below affected timber, trailing down from holes, or settling on things stored underneath.

The hole appears years after the damage

The flight hole is an exit, not an entrance. A larva tunnels inside the timber for three to five years before pupating and eating its way out. So by the time you see a hole, that particular insect has finished - and the question is whether others are still inside.

Which is why frass matters more than hole count.

Where to check

• Subfloor bearers and joists, especially on the damp south side
• Floorboards, particularly in older untreated native timber
• Roof space framing
• Skirtings, architraves and door frames in older homes
• Furniture, especially older or inherited pieces

Some boards, not others

Completely normal. Borer prefer soft sapwood and untreated timber; the untouched boards beside affected ones are usually harder heartwood. It doesn't mean the treatment failed or that the inspection was wrong.

It might not be borer

Three insects attack New Zealand building timber - house borer, two-toothed longhorn, and the native drywood termite - and they leave similar-looking damage but don't all need the same treatment. Hole size and shape is the main tell, which is why identification comes before any quote.