How to Tell If a Wood Beam Has Old House Borers?

How to Tell If a Wood Beam Has Old House Borers?

You can check whether a wood beam has old house borers using the following methods. Inspect your structural timbers at least once a year.

Method 1: Look for holes and frass

When adult old house borers emerge from the wood, they leave distinctive exit holes:

• The holes are oval-shaped, not perfectly round like those of common wood borers
• The holes are about 1–2 cm across—wide enough to fit your fingertip
• Coarse wood shavings and fecal pellets collect around or below the holes
• The frass is close to the wood’s natural color and feels rough

Method 2: Tap and listen

Tap the beam with a screwdriver or small hammer:

• A sharp, clear sound means the wood is relatively solid
• A dull, hollow sound means the inside may be hollowed out
• If a large area sounds hollow, the situation inside is serious

Method 3: Probe with a screwdriver

Gently press a screwdriver into the wood surface:

• Feels hard and solid — the wood is intact
• Feels soft or the tip sinks in — the inside has been hollowed out
• You break through the surface and see tunnels inside — confirmed infestation

Method 4: Listen for chewing

On a quiet summer night, put your ear close to the beam and listen:

• If you hear a distinct crunching or clicking sound of larvae chewing wood
• That means active old house borer larvae are feeding inside
• The sound is clearest at night

Method 5: Check beneath the beam

Regularly inspect the area directly under the beam:

• Is there fresh wood dust falling?
• Are there coarse, granular droppings?
• If yes, old house borers are actively feeding right now

How often should you inspect?

Do a thorough inspection at least once a year. For older homes and timber-frame houses, inspect every six months. Focus on roof beams, attic timbers, and basement structural wood. Summer and fall (June–October) is when adults emerge and larvae are most active—this is the easiest time to spot problems.