Woodworm is not an organisation in itself; it is a term describing the infestation of wooden furniture by any of a number of beetle species. These insects cause damage to timber at two stages of their life cycle: first, when the grubs emerge from their eggs and start burying down into the wood, and then, when the adult beetles emerge by boring exit holes.
Three of the most common pests to infect timber are furniture beetles of the genus Anubium, the death watch beetle (Xestobium rufovillosum) and the powder post beetle (Lyctus brunneus)
Common furniture beetle
The most numerous of the Anubium genus is the common furniture beetle, Anubium Punctatum, and in some parts it is rare to come across a building more than 20 years old without its presence. A. punctatum is not usually found in timber less than 10 years old.
The adult beetle can measure from 2.5mm to 5mm in length and ranges from red to brown-black in colour. It is recognisable by its hooded thorax which hides its head from above. Its upper body is covered in short yellow hairs and there are breathing pores visible on its wing cases.
The female deposits eggs in grooves and when the grubs emerge they begin to tunnel into the wood as they feed, creating ‘galleries’ and a fine, sand-like dust . The six-legged grubs are white and crescent-shaped with a bulbous terminal segment. After one to three years, the winged insects pupate and exit the wood via 1.5mm exit holes. They can often be seen from May to September sitting on window sills.
Treating A. punctatum infestation is a matter of treating all infected timber, and any adjacent wood, with insecticide. Care needs to be taken to ensure all cracks, joints and hidden areas are treated, particularly unpolished leg ends, the undersides of tables and drawers and the back of cabinets cupboards, inside and out. The chemical should be applied by brush or spray, but not an atomiser; flight holes can also be injected using a fine nozzle. Finally, the furniture should be thoroughly polished to prevent the holes being re-used in the future. In cases of serious infection, the wood may have been weakened too much and will need replacing.
Death watch beetle
The death watch beetle (Xestobium rufovillosum) rarely attacks furniture unless the wood has been decayed. The larval period is around three years, but in warm, humid conditions, and if rotten wood has been considerably broken down by fungus, this time can be much shorter. Since the death watch beetle prefers hardwood to softwood, they tend to be less of a problem to homeowners, but their size and the depth of their boring causes more damage. Structural timber used in churches, boats and old barns are more likely to harbour death watch beetles and these are often also infested with furniture beetles.
The largest members of its family are 6mm to 8mm long and chocolate-brown in colour, with patches of yellow hair often giving them a variegated appearance. Eggs are lemon-shaped, white in colour and half a millimetre in size; the female lays them in cracks, crevices and old exit-holes. The larvae are over 6mm in length, curved and white with fine yellow hairs. Their bore-holes are 3mm in diameter and each will contain a small pellet.
Infected timber should be removed and replaced if necessary with the remaining wood scraped, vacuumed and treated with insecticide. New timber should also be treated. Two applications should be carried out, using a brush or non-atomised spray. This will need to be checked annually for four years.
Replaced wood should be sound and seasoned (not sapwood, as this is vulnerable to fungus and insect attack) and softwoods should at least be surface painted with a fungicide and insecticide-containing preservative.
Powder post beetle
Rather than old and rotten wood, the powder post beetle (L.Brunneus) targets recently died or unseasoned hardwood timbers with large enough pores to enable egg-laying. Starch in the sapwood sustains the larvae, so if wood is too old they won’t be able to survive in it. Their presence is sometimes seen as a fine powder on wood stacks stored in timber merchants’ warehouses.
This slender brown beetle is differentiated from the others mentioned in that its thorax doesn’t protrude over its head and, at its widest, is as wide as its abdomen. One spindle-shaped egg is laid in each pore, out of which curved white larvae with yellow heads and dark brown jaws emerge.
Most infected sapwood will need to be burned as it is not suitable for furniture, although kiln-drying before use will sterilise it. Most treatment for post powder beetle is preventative, consisting of adding a poisonous and repellant insecticide to kill the insects and deter females from laying.