Firstly, the word “Woodworm” is generally used as a collective term to describe what we generally prefer to call “wood-boring insects”. It is a term which refers to the larvae of a wood-boring beetle that looks a bit like a worm. When talking about woodworm, or wood-boring insects which cause damage in buildings, there are usually 4-5 different species we tend to deal with. These are:
- Common Furniture Beetle (Anobium Punctatum)
- Death Watch Beetle (Xestobium Rufovillosum)
- Wood-boring Weevil (Euphryum Confine and Pentarthrum Huttoni)
- House Longhorn Beetle (Hylotrupes Bajulus)
- Bark Borer (Ernobius Mollis)
Where timber has been infested by any of these beetles, there are tell-tale signs we look for and these are generally the exit holes made by the insect and each insect makes a different sized exit hole. We also look for deposits of “frass” both around the exit holes and on surfaces underneath the visible exit holes.
For the purpose this blog, we will deal with the insect most people tend to refer to when mentioning “woodworm”, which is probably going to be the Common Furniture Beetle. The typical signs of infestation are visible holes in the timber, which are the exit holes made by the adult beetle, when eating it’s way out from the pupal chamber. Prior to that emergence, or exit hole, the insect will have been actively tunnelling it’s way through the affected timber for a period of around 3 years. Once new eggs are laid onto timber, they will hatch and the larva will begin it’s life tunnelling through the timber until it is ready to pupate. At that time, it forms a pupal chamber, where it turns into the adult beetle, who will then eat it’s way out of the timber, leaving the visible exit hole. The male and female beetles will then mate and the female will lay her eggs for the whole cycle to begin again.
This insect can and does infest timbers throughout properties. Generally, this insect will attack timber (softwood and hardwood) with a relatively high sap content. It will usually affect the sapwood of the timber unless fungal decay is also present, when it may also affect the heartwood. Timbers affected by dampness caused by rising or penetrating damp, which result in the moisture content of the timber being raised, are also more susceptible to wood-boring insect attack.
What you need to be looking out for are small round exit holes. The holes will be similar in sizes to the holes in a dart board (approx 2mm). However, whereas the holes on a dartboard are made from something puncturing the surface from the outside, the exit holes from Common Furniture beetle are made from the insect coming out of the timber; they are therefore very clean-cut around the sides of the hole. Depending on the level of the infestation, you may need to have a very keen eye to identify all the areas. To give you a better idea of what to look out for, please review the picture to the right.
Frass, or bore-dust, from the Common Furniture Beetle is generally cream-coloured, although can be darker dependent on the type of timber infested. This frass is made up of tiny lemon-shaped pellets which is gritty when rubbed between the fingers. Even if you cannot see any holes, you might find frass escaping from the back, or the underside of old furniture, which could suggest an active woodworm infestation. The picture to the left indicates what frass looks like.
Other signs to look for
Another sign to look for, where you think you may have an infestation of wood-boring insects, is crumbly edges to floor boards and joists. This is caused by the breakdown of the cellular make-up of the timber from the tunnelling within which, as mentioned earlier, can be happening for approximately 3 years – per larva!
Depending on the type of timber affected, it is sometimes possible to see a variety of small tunnels that have been bored into the wood. This becomes very noticeable on wooden floor boards which have been sanded in readiness for varnishing. The act of sanding the timber down removes the top 2 or 3mm of floor board, which can often expose some of the tunnels made by the larval stage of the insect. The following pictures indicate this:
Is the infestation active, or not?
The reality is, an awful lot of woodworm infestations have been treated over the past 40-50 years and if the treatment was carried out properly, in most cases, there should not be a re-infestation. It is always useful for us to know if an infestation has been treated previously and also, where possible, when that treatment was carried out. One thing a treatment does not do, is to remove the old exit holes from the timber.
When an infestation is found, one thing we tend to look at is the general colour of the visible emergence / exit holes in the timber surfaces. More-often-than-not, where the holes are dusty and the same colour as the outer surfaces of the timber and there is no visible evidence of frass (or bore dust) they are likely to be old. Fresh holes from a recent active infestation in old timber tend to look very clean and bright because it is possible to see the original timber colour within the hole. We are also looking for signs of frass around the hole and on surfaces underneath any holes.
The other thing which comes into play is the flight emergence period, which, for the Common Furniture Beetle is usually from around May through to August / September. So! if you see just a few holes – maybe in a cupboard underneath stairs – it may be a good idea to fill the exit holes which are visible with beeswax and wait for a year to see if more appear the following year.
If you are lucky enough to actually see beetles emerging from timbers then take this as a clear tell-tale sign there is an active infestation.