What is woodworm?
Woodworm refers to the larvae of any wood-boring beetle, rather than one particular species. In the UK, the most common are the Common Furniture Beetle (Anobium punctatum), Deathwatch Beetle (Xestobium rufuvillosum), House Longhorn Beetle (Hylotrupes bajulus) and Powderpost Beetle (Lyctus brunneus). All invade and consume wood, and then leave when they have reached maturity.
How do I know if my property is affected?
Your woodwork may be harbouring woodworm without you knowing it. Wood can be infected with eggs or larvae without it being noticeable, and you may not discover a woodworm infestation for several years. It's a common misconception that woodworm only affects old properties, in fact it can cause damage to newly constructed buildings.Tell tale signs of woodworm include:
- Small round holes in your woodwork, similar to the holes in a dart board.
- Fine, powdery dust around these holes (this is known as frass).
- Crumbly edges to boards and joists.
- Adult beetles emerging from the holes or present around the house.
Even if you can't see any holes, you might also find frass escaping from the back or underside of old furniture. Again this suggests active woodworm.
>However, not all of these signs of activity are cause for concern. Holes and frass might just indicate a previous woodworm infestation, long since dormant. The following tips are to help you confirm whether you have a serious, current problem:
Not all woodworm are harmful - consult a professional entomologist to identify the woodworm before you decide on treatment. The British Pest Control Association offers an insect identification service.
Adult beetles are responsible for boring the holes when they exit the wood to breed. This happens between May and September, so a good idea is to block the holes during the winter by painting with a coat of emulsion, or applying masking tape. In the spring, you can check if any beetles have emerged and therefore determine whether you have active woodworm in your timber.
Test the humidity of your woodwork using a timber moisture meter. These cost about £50 but you can hire one from a hardware store. Insert the probe and you'll get an instant moisture content reading. A moisture content of 20% would be a cause for concern. Woodworm prefers timber with moisture content over 18 %, although it can tolerate moisture contents as low as 12 % for short periods.
At lower moisture levels, however, the rate of colonisation tends to be low and infestation will die out with prolonged periods of reduced moisture levels. (Ref: Helen Sellars/Sophie Hale, Forest Research, Midlothian). You can assume that a reading of 11% puts you at very low risk of a woodworm infestation.
Measures to prevent woodworm infestation
- Keep humidity levels low and ensuring wood is well-ventilated. See above for advice on checking moisture content of your timber.
- Remove pieces of furniture or non-structural timber that are infested to avoid the woodworm spreading.
- Install electric fly traps in loft spaces and under-ventilated areas to kill emerging adult beetles in the summer months, and thus reduce the threat of infestation.
How much damage can woodworm cause?
The amount of harm caused by woodworm will depend on the species of beetle and the type of wood.
Common Furniture Beetle
TAttacks softwood (conifer) and the sapwood of European hardwoods. Rarely causes structural weakening although tunnelling along the grain of the wood can potentially cause extensive collapse.
House Longhorn Beetle
TOnly attacks the sapwood of softwood timbers. As softwood is often used in roof timbers, infestation can often result in severe structural weakening. The good news is that this species is now rare in the UK.
TCauses damage to wide-pored hardwood with a high starch content, such as ash, elm and oak. Older timbers (over 15 years old) don't provide a suitable environment for this species. Tunnels along the grain and can cause severe damage, often infesting block or parquet flooring.
TPrefers European hardwoods, especially oak, ash and chestnut that has been “softened” by partial decay. The larvae tend to tunnel towards the centre of the timber, so that damage may be more extensive than is apparent from the exterior. In the UK, this species is concentrated chiefly in southern/central England, and is virtually absent in Scotland.
What treatments are available?
TSo you've found evidence of woodworm. Before deciding on a treatment, you should:
- Identify the species.
- Determine whether the infestation is still active.
- Employ a timber specialist or qualified surveyor to determine which timbers have been structurally weakened and need replacing.
Timber that has been structurally weakened will have to be removed and replaced with pre-treated timber. Other affected woodwork will then need to be treated. Small-scale treatment can easily be carried out as a DIY job, but professional advice is recommended for the treatment of larger scale infestations and certainly for removal and replacement of large timbers.Methods of treatment include:
- Surface application of pesticides.
- Freezing – only suitable for items of furniture infested with woodworm.
- Fumigation – usually appropriate for Deathwatch Beetle infestation in large structural hardwoods. The adult beetles are effectively “smoked out” during the annual flight season.
Many of the most effective insecticides can only be obtained by certified professionals. Some are not advisable due to their toxicity and potentially damaging effect on human health and the environment. While it's tempting to opt for a blanket treatment, this may not be the greenest choice. It's worth bearing in mind, for example, that treated timber is considered toxic waste at the end of its lifespan and must be disposed of accordingly.
Between 50,000 and 150,000 remedial timber treatments are carried out in British homes each year, many of which may be unnecessary. Overuse of toxic chemicals in residential settings puts occupants at risk so it's preferable to avoid unneeded repeat treatments. You can contact Property Guarantee Administration, a company which can identify active timber treatment chemicals from a small timber sample which you send them.
A laboratory analysis and report costs £95.00 plus VAT per sample. This could eliminate the unnecessary use of pesticides in your home as well as saving you a substantial sum of money if further treatment proves unnecessary.
A safe but effective treatment is borax, a compound of boron also known as sodium borate. This is available as a crystalline powder, which is dissolved as a 15% solution in water and applied to the affected timber. There are no health hazards associated with this treatment, and borax will inhibit fungal growth as well as killing woodworm.
Ensure that your woodworm problem has been clearly diagnosed before agreeing to chemical treatment and remedial work. Unfortunately timber treatment contractors are not legally required to complete any training or certification.
In 2002, a 39 year old man died during a routine fumigation to treat woodworm in the roof of a church in southern Germany. The chemical used was sulfuryl fluoride, a highly toxic gas that has no odour or colour. There's no need for alarm, but pesticides are potentially dangerous and you should ensure that the contractor:
- Informs you which chemical treatment will be used and how it will be applied. As mentioned above, some can be environmentally unsound. Avoid lindane, pentachlorophenol (PCP), tributyltin oxide (TBTO) altogether - acute exposure to these chemicals can cause ongoing medical problems.
- Informs you of any appropriate training.
- Is a member of the Property Care Association, part of the British Wood Preservation and Damp Proofing Association. You can find a PCA contractor member at www.property-care.org.
- Uses PPE (personal protective equipment).
- Gives you a guarantee for the work.
What costs are involved?
For an average house, you're looking at £500-£1,000 for blanket pesticide treatment.
An application of borax solution is relatively cheap – around £28 per 25 square metres for surface treatment of a light to medium woodworm infestation. Boron-based paste or gel is slightly more expensive, while leave-in rods that remain in timber suffering from permanent or seasonal dampness cost around £16 for 10.
Permethrin-based treatments are cheaper – 1 litre of the popular Microemulsion Woodworm Killer Concentrate costs £7 and makes 25 litres, sufficient to treat 100 square metres of timber.
Repairing woodworm damage
After woodworm has been eradicated, structural woodwork should be replaced with pre-treated timber. Non-structural timber, including furniture, can be tarted up once the treatment is complete. Some people find that a peppering of flight holes gives woodwork character!
If you don't, try filling holes with a mixture of beeswax and turpentine or a commercial wood filler. Many beeswax furniture polishes provide protection from future larval infestation. For painted wood, fill the holes then sand the surface down and redecorate.