Yorkshire Dampcourse home page :: Woodworm


and Wood-boring Beetle Attack

Insects that attack timbers do so mostly in forest and woodland habitats. We fill our properties with timbers as a building material and effectively lay out the insect’s food material in extensive amounts (joists, floorboards, joinery and roof timbers) available for insects to infest. We encourage attack further by placing these timbers in areas where dampness can occur e.g. ground floors and roofs, and sometimes in areas where leakage of water onto local timbers can occur too e.g. bathrooms and kitchens. However, timbers do not necessarily need to be damp to become infested. 

Woodworm attack to floorboards

Pre-treatment of timbers with insecticide will prevent infestation but in older properties treated timbers have not usually been used in the original building. Design features of older buildings might encourage dampness to occur and insect infestation in these older properties is not unusual.

Treatment/replacement of timbers requires specialist advice to ensure the correct treatment is given (some insect attacks do not need chemical treatments), and this relies on correct identification of the infesting insect.




The most common insect attack is by wood boring beetles. These are insects that rely on timber as a food source. Where beetles attack timbers, the usual description of the attack is described as "woodworm". This is because the larvae of the beetle looks like small cream-coloured worms. It is the larvae that do the bulk of the damage to the timbers.

Use of insecticides is governed by Acts of Parliament (law) and Health and Safety Regulations and this requires specialist knowledge. Timber replacement must follow existing Building Regulations and guidelines to make sure that the timbers can perform structurally to specification.

The photo above shows holes in the timber made by emerging adult woodworm beetles. This emergence takes places usually in the warmer months of summer.

Woodworm attack to irtchen floor

This photo shows that sometimes damage from woodworm can be very severe - and dangerous. In this case the client went through the floor and it was only the linoleum covering that stopped his foot carrying on going into the cellar.

Although not obvious, this floor is relatively new. Who ever replaced the original floorboards failed to treat them against woodworm attack, so the woodworm "chomped away" at lovely timber presented to it in the slightly damp cellar below.




Our work to deal with insect attack to timbers always starts with a visit to site to inspect the problem. Sometimes no treatments are recommended, either because the infesting insect does no structural damage or because an infestation looks old. There is always the strong possibility that a past treatment has already successfully been undertaken. Surveyors and companies are not allowed by law (Control of Pesticides Regulations 1986) to recommend unnecessary timber treatments and must justify clearly any use of insecticides.

Severe woodworm damage to floorboard

Tests for already treated timbers can be carried out. A flame (Beilstein) test  will determine the presence of halogenated materials in timber. This would detect, for example, the use of an organo-chlorine insecticide. These were used in the past as insect treatments, but are now only used by qualified people under the direction of qualified surveyors. They have been replaced by the permetherin and boron insecticides. Tests for the newer insecticides are also possible and material needs to be sent away to a laboratory for this. We are able to arrange for  these tests to be undertaken. We charge for this service.

Determining if an infestation is active is difficult. It is not sufficient just to see woodworm holes or to detect frass falling from the timbers. Once the woodworm holes are there they never go away and frass can be dislodged from timbers years after a successful treatment. However, these are both indications of a potential problem, which is why you need expert advice.

The photo above shows severe localised woodworm infestation. The problem was out of sight beneath a carpet. A chair leg went through the floor revealing the infestation and the damage. In this case the floor was treated and those weakened floorboards that could be identified were replaced with new treated timber.

 The flight season of woodworm is in the warmer months of May to September, with a narrower range (say June to August) in more northern areas. The best proof of an active infestation is to see live beetles or to find them dead on window ledges or other surfaces. You will need an expert to identify them, as they can be confused with the many species of carpet and other beetles that live in our properties. They are attracted to light and tend to be drawn to lighter coloured surfaces and windows. Real evidence of an infestation should be gained before deciding to treat. Why spend money on treatments that have already been successful ? The treatments may also still be under guarantee from the company who did the work. Such guarantees are usually in force for between 20 and 30 years.  


Where a treatment is recommended/required then this is usually a water based insecticide applied by a low pressure spray directly onto the timber’s surface. An alternative is the use of gels or pastes often applied close to inaccessible timbers (e.g. joist ends) with the ability of the compounds to diffuse into the inaccessible timber. Various chemicals are presently in use and include permetherin (a synthetic pyrethroid), boron (a naturally occurring mineral compound) and a relatively new group of chemicals which inhibit normal insect development (growth regulators).

Woodworm damage this severe usually requres timber replacement

Spray treatment to timbers is a relatively easy process, but is disrupting to the property occupants as everything (carpets, other floor coverings, furniture, fixings and etc.) has to be moved, or movable, to gain access to the surface of the timbers to be treated. After spraying Health and Safety regulations requires the minimum of 8 hours to elapse and surfaces to be dry before re-entry to a treated area and its reinstatement to habitable use. There are insecticides now available where a 1 hour re-entry has been granted, but this is still dependant on the timber being dry as well. Drying out is unlikely to be that fast unless it is forced. We prefer to consider the 8 hour "rule" as being the one to apply.


Recent reformulation of timber treatment fluids for woodworm now means that they are virtually odour free. Some slight smell may be noticed immediately after treatment, but this quickly declines with drying and improved ventilation.

The photo above shows woodworm damage to a structural timber that is so severe that the timber will need to be replaced or strengthened in some other way - usually by adding steel plates or a secondary timber along side to share the loading.

 Wood boring weevil damage to floorboard

This photo shows characteristic striated damage to timber by wood boring weevil. This is one of the wood borers that does NOT need chemical treatments.

Wood boring weevil is usually associated with timbers that are already suffering from wood rot. The beetle infests because the timber is partly digested by the rot.

Such timbers are usually replaced with treated materials, without the need for the application of insecticide to the original timber.

If there is a mild attack, and the timber can be isolated from future damp, isolation will allow the timber to dry out, wet rot attack to halt, and the lack of moisture will cause the weevil to die out.


Correct diagnosis and correct treatment is the key to dealing with these problems - that is why it is always best to contact a specialist. 


House longhorn goes on holiday House longhorn has been identified in a wooden cot leg in Blackpool!

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