Doctor on the house: The hole truth about woodworm

I have come across an interesting passage in a decorating book called Period Finishes and Effects. It reads: "Evidence of woodworm infestation can be effectively simulated by making clusters of small holes with a nail or the point of a compass." So now it becomes clear - half the population is trying to make new wood look old by poking holes in it, and the other half is spraying the holes with nasty chemicals in case something pokes its head out and bites them. You couldn't make it up.

As it happens, a friend called last week to ask what to do about his woodworm. He's a building surveyor by profession, so naturally he doesn't know anything about timber infestation.

Like most people, he assumed the little holes in the edges of his floorboards were evidence of wood-boring insect attack. I told him that the holes may well be evidence that the boards once had woodworm, but since they are known in the trade as flight holes, what they actually indicate is that the insects have now scarpered. It is the larvae - the maggot stage - of Anobium punctatum that do the munching, and they do it below the surface of the timber. After a couple of years they pupate into little chrysalises, and then they hatch out as adult beetles, chomp their way to the surface and take off into the wild blue.

So why do surveyors think flight holes - or compass holes, as we shall now call them - are evidence of continuing insect attack? After all, active infestation is easy to confirm - the munching larvae produce faeces which consist largely, you will not be surprised to learn, of wood. It looks like sawdust, feels gritty if rubbed between the fingers, and can be collected on a sheet of paper under the suspect area.

I have made one or two observations about woodworm: first, Anobium's staple diet is sapwood - the outer, growing, part of the tree. They like the sapwood because it is moist and nutritious, so they hang out in places where there is plenty of fresh sapwood available - forests, for example. Now, while they are in the egg stage, they may suffer the indignity of being in a tree which is sawn up and carted off to be used as building timber. For as long as the timber retains enough moisture, they will carry on with their munching and burrowing, complete their normal life cycle and then buzz off, leaving flight holes behind them.

But by that time the timber will have dried down to an unpalatable level, especially if it is in a centrally-heated building, so there is little attraction for the female beetles to lay their eggs in the same spot; they'll be off outside looking for a nice fresh juicy tree. I suspect that most woodworm damage occurs in this fresh timber, probably in the first couple of years after the house is built; and since it is confined to the sapwood at the edges of boards and joists, there is rarely any structural weakening, and so no real problem.

Also, the term timber "infestation" can be confused with "infection". It makes woodworm sound like some kind of contagious disease. I've known people who bought old furniture at auctions get paranoid that they've imported woodworm into their homes - they think the little blighters are going to spread out and eat the whole house, so they've sprayed chemicals everywhere. Left to themselves the woodworm will probably clear off - it's the long-term effects of the chemicals that are starting to look like the real problem.