Woodworm and Timber pests

The existence of timber framed buildings dating back from the medieval ages and the widespread use of timber in modern structural applications (floor joists, roof purlins etc.) has emphasised the risk that Woodworm and other timber pests may pose. Consequently, if left untreated, these insects can cause significant damage, which can result in catastrophic results.

Many people confuse the term Woodworm with a beetle species type, however the term is actually a generic reference to the beetles during the larvae stage of their lifecycle, which is the period when beetles cause timber decay.

There are a number of different beetles, which can cause damage to timber; these include Common Furniture, House Longhorn, Deathwatch beetles and the Wood boring weevils. Please see the article, identification of beetles in building timbers.

Woodworm generally needs favourable conditions in which to propagate, with damp unseasoned timber being most at risk. Incidences where timbers have become wet, through e.g. a roof leak, drainage or plumbing problem, which has been unresolved for a considerable time, may result in insect infestations.

Insect Infestations can affect properties of all ages, although this is most prominent and severe in older buildings which are no longer used and heated, whilst still contain untreated and exposed timber e.g. floor joists imbedded within the wall etc

The main risk with Woodworm is the threat of structural damage, through the displacement of timber, a result of insect burrowing and feeding, creating fissures and cracks, which can significantly weaken a structural timber beam.

How to identify Woodworm?

There are tell tale signs to look out for, when inspecting timbers for the presence of woodworm and or beetle infestation.

The most important consideration is whether the infestation is live or not. This is difficult to ascertain from the untrained eye alone, however there are key aspects to look out for, as outlined below.

These include:

  • Clean, pale Exit holes (or flight holes/ Compass holes)  – This indicates the beetles have emerged for mating. Identify size and shape of the holes to ascertain beetle type. Old flight holes may have become darker with age.
  • Fissures, Cracks – Beetle larvae often create tunnels, which appear as fissures or cracks, as they burrow to the surface. Although, this should not be confused with shrinkage cracks, from the natural wood drying process.
  • Bore Dust (Frass) –The faeces of active woodworm, which are often left, as the beetle has eaten its way out of the wood to the surface. This appears like gritty sawdust. Dust may also appear beneath the timber surface, and may be more pronounced at different times of the year.
  • Favourable conditions – The ideal conditions for beetle infestation is newly seasoned ‘fresh’ green timber, which has been left in damp, unvented and humid conditions. In such conditions, it is also likely that you may find wet/ dry rot and other nasty problems.


It should also be borne in mind that evidence of flight or exit holes, does not conclusively mean a live infestation is present, merely indicating that woodworm has occurred in the past.

Flight holes may be a false indication, as it has been known in the past, that purpose made holes have been made to give timber character, particularly, but not solely to furniture, which are created to give the impression of aged, distressed wood.

In hardwoods, not all parts of the timber may be affected, as woodworms will generally target nutrient rich sapwood, leaving the resistant heartwood relatively untouched. However, the presence of fungi can change the chemistry of timber, allowing the larvae to exploit and decay more resistant heartwoods. 


Woodworm treatment

It is important, that the species of beetle is identified before remedial treatment is carried out; this is because different species responds in different ways to Insecticides and other treatments, similarly treatment may not be needed.

There may be flight holes, which have been caused by the beetles, such as Powder post or Pinhole, whom only infect new green timber and will subsequently die out as the wood dries out in use. 

Another type of beetle, the Wood boring weevils only affects decayed timber, which has been partially broken down by the action of Dry/ wet rot. As such the most effective cause of treatment in this instance would be the removal of affected timbers, and eliminating the source of damp.

Generally the most effective method is to carry out preventative action, whereby, ensuring your home is adequately heated and ventilated all year round. For exactly this reason, in modern, centrally heated buildings, Woodworm is much less common.

Woodworm can be treated with a suitably applied Insecticide treatment, applied either as a paste, in a fluid or as a gel and can work in different ways, with some targeting the larvae directly, others cause the timber to become toxic, and some prevent the development of the beetle.

Insecticide treatments can be very effective if applied correctly, and may last many years. Many specialists are available who provide such treatments, and provide guarantees for such works.

Their effectiveness however may be compromised if the timbers become damp, as a result of a leaking roof or gutter, as such, consideration should be made to ensure, the original defect, which caused the timbers to reach the warm, moist conditions are not prevalent again.

Another option is to adopt a smoke treatment, which kills live adults in the vicinity and leaves a toxic residue on the affected timbers. There are, however practical difficulties with this, particularly around accessing the infected timber members, which need to be spray applied, and are often in inaccessible areas such as loft areas or floor voids.

If the outbreak has been severe, the timbers, (which may be floor joists/ roof trusses) may be so badly affected, that they need to be replaced. Replacement with a suitable hardwood would then be advised, to reflect their increased resistance to Woodworm and other similar defects.

Further advice

For further advice and or information, please contact us: Alternatively, you may wish to contact the companies in the resources section.