The majority of cases of woodworm holes are due to long gone infestations, and are quite harmless. A high percentage of pre-1900 buildings have minor historic woodworm damage.
Holing is less often caused by active infestation.
Woodworm like holes can also be caused by drawing pins.
Prevention of Woodworm
- Avoid building with sapwood
- Resolve any genuine damp & rot problems
- Avoid build up of soil or debris against wood
Prevention of resulting problems
- Avoid sanding old floorboards, as revealing worm tracks makes them look pretty bad.
- Avoid spending money on expensive and toxic treatments when they are not normally needed.
- Bear in mind that woodworm does not normally threaten a building's structural integrity, so there is no urgent rush involved.
- Be cynical of pressure and panic from salespeople with pound signs in their eyes.
In cases of old infestations, no treatment against woodworm is necessary. Timber only needs to be replaced if it is very badly wormed. Timber may also be replaced for cosmetic reasons.
The first thing then is to determine whether the infestation is ongoing or historic. A very effective way to do this is to stick paper over the holes, and wait till spring when the beetle larvae emerge. If the infestation is active, the paper will be covered with holes when they burrow out. If more or less no holing occurs, there are no woodworm present.
Active infestations may be controlled by
Note that these control measures only kill insects when they finally emerge, at which time the damage is already done. Prevention of further attacks may be more useful.
From Pesticide Safety guidance page:
When is a pesticide necessary?
The decision to apply a pesticide should only be made after careful consideration of problem. This will include: pest identification, damage, and probable degree of infestation. Alternative measures such as better housekeeping, improving ventilation, biological control or integrated pest management (IPM) should always be considered. Anyone without the competence to decide these issues should seek advice from an expert