PESTWATCH | PPC104 AUGUST 2021

We’ve had a few requests for information on the highly-specialised property care pests - wood-boring insects. The Property Care Association takes over our usual feature with an introduction to wood-destroying insect pests.

Finding signs of wood-boring beetles during a survey, particularly on older buildings, is not uncommon. While inevitably their presence will cause concern, attack by any of the wood-destroying beetles found in the UK can be treated.

Prior to undertaking any form of treatment, it is essential to establish if the infestation is active or historic. All timber should be investigated by a suitably qualified professional to determine evidence of current activity to justify any form of treatment.

The insect may have already died out due to unsuitability of the timber, decreased moisture content or previous treatments. In these instances, treatment will not be justified.

This article highlights signs of activity from some of the more common beetles, their identification, and where to go upon their discovery.

Common furniture beetle (Anobium punctatum)

This is the most abundant of the wood-destroying insects found in buildings in the UK. Naturally, it inhabits dead and fallen branches.

The beetle is significant because of its abundance and given the right conditions it can infest a wide variety of timber products, including structural building timbers, and furniture.

If left unchecked, in the right conditions, infestations can lead to severe structural weakening and eventually total collapse.

Adult beetles are 2.5-5mm long and are reddish to blackish-brown.

The upper parts of the body are covered with fine, short yellow hairs. The rows of small pits or punctures on the wing cases are well defined.

Adult beetles emerge from timber in the spring and summer. Females lay eggs, typically into cracks and crevices in the timber.

The larvae slowly burrow under the surface of the timber for two to four years. It is this phase that is most destructive to the timber.

If left unchecked, in the right conditions, infestations can lead to severe structural weakening and eventually total collapse.

Active common furniture beetle infestation

It’s the appearance of new emergence holes (typically 1-2mm diameter) and the dust (frass) that falls from them that often indicates the presence of an active infestation of woodworm.

The frass is similar to fine sand and other indicators include the presence of adult beetles and larvae in the timber. Most damage will be found in timber that has been in use for 10 years or more.

Adult beetles are capable of flight and this enables them to infest other timbers. From March to September, adults can be found on the window ledges of houses containing infested timber.

Mistaken identity?

The common furniture beetle could be confused with these ‘usual suspects’:

Bark borer beetle (Ernobius mollis)

Sometimes building timbers, particularly rafters, are used with the bark adhering to them. If holes are found in the bark it may lead householders to think that Common Furniture Beetle is present.

The beetle responsible is Ernobius mollis. The workings are confined to the bark and there is no risk to other parts of the wood from attack.

Ptilinus beetle (Ptilinus pectinicornis)

Infests European Hardwoods and damage often originates in the sawmill or timber yard. Uncommon in buildings but when it is it’s mainly found in furniture items. Emergence holes are 1-2mm in diameter. Bore dust is densely packed in tunnels and not easily dislodged. Treatment with approved insecticide when replacement is impractical.

Powderpost beetles (Lyctus (lyctidae) and bostrichidae (false powderpost beetle))

Of the Lyctidae, Lyctus brunneus and Lyctus linearis typically occur in the UK. Lyctus beetles are found in unseasoned or recently dried hardwood timbers, principally oak.

Like common furniture beetles, the exit holes are about 1.5m but are usually filled with a fine flour-like bore dust (frass) – this differs from common furniture beetles where the frass is coarser, lemon-shaped and gritty.

Other common UK wood destroying insects

Wood boring weevil

Arguably the second most common wood boring beetle encountered in the built environment in the UK.

Adults are 2.5-5mm long, reddish-brown to blackish, with a snout (rostrum) and long flattish body.

Life cycle is short at around 12 months and, unusually, adult beetle also lives for around 12 months. Adults therefore feed and leave characteristic striations (channels) on the timber surface.

Wood boring weevils are restricted in their activities to damp and, at least, partially decayed timber. They are often found behind skirting boards and decaying wall plates where fungal decay is present.

Thus, they are normally brought under control by measures taken to deal with wet rot.

Deathwatch beetle (Xestobium rufovillosum)

Its preference for certain partially decayed hardwoods, principally oak, means it is most commonly found in historic buildings, such as churches.

The best indicator of an active infestation by deathwatch beetle is the presence of adult beetles, typically found on surrounding floors. Surveying during the flight season, typically between April and June, is advisable.

Timber damage can be easily distinguished from that of other wood-boring insects by the presence of small bun-shaped pellets in the frass produced by the larvae and noticeably larger (3mm) flight holes.

The beetle is 5-8mm long, and is dark chocolate brown with patches of short yellowish hairs, which give the insect a variegated appearance. In old specimens these hairs may have been rubbed off, in which case the mottled appearance is less obvious.

Treating an infestation by deathwatch beetles can be particularly troublesome.

Treatment with an insecticide by brush or spray during the emergence period of the beetle is useful in destroying eggs and young larvae before they enter the wood, but it is doubtful whether such treatment will kill older larvae working below the surface at any considerable depth.

Property Care Association

Members of the Property Care Association (PCA) that specialise in timber preservation are the recommended first port of call for practical advice on infestations from wood-destroying insects.

The ability to implement the correct and appropriate remedial treatments can save huge sums of money that would have otherwise been spent on expensive structural repairs.

PCA members who specialise in timber preservation are proficient in a number of techniques that can be utilised to control beetle infestations.

The PCA’s nationwide list of contractor members are carefully vetted before being awarded membership and are then subjected to rigorous ongoing auditing procedures once admitted to the association.

Members of the PCA can offer insurance backed guarantees for much of the work they undertake.

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Source: PPC104