Common Furniture Beetle…

It’s a small chappie, probably no more than 3-5mm in length, with a dark-brownish colouration.  If you have a look at it under a magnifying glass, you can see distinctive lines of dots on its wing coverings (elytra), running from head to tail. With the naked eye, it’s easy to confuse it with other insects, so care is needed for identification.

Basically, this insect is a forest dweller; but enabled by its ability to fly, and thus drift around in the soft arms of summer zephyrs, it long-ago moved up-market where it now occupies a position as one of our many, unwanted house guests.  Although it can often cause disfigurement to timber - because it gets its sustenance from sapwood, not heartwood, it is seldom structurally significant.  It will dine equally well on both softwoods and hardwoods.

This is quite important, because roofing timbers, such as the oak beams that are often found in older properties invariably have heartwood as their significant component. It is quite common to see the outer surfaces of these timbers pockmarked with flight holes or galleries; although the only significant, beetle activity has occurred within the outer 20mm or so. The heartwood core is completely untouched and the [usually oversized] beams are not structurally compromised at all.

This effect can also often be seen in floorboards, where the outer edges can sometimes be damaged beyond repair.  The heartwood centre of the board, be it softwood or hardwood, is untouched.  The photo below illustrates this.

There are many excellent articles on the Internet that deal with the life cycle of these insects but other than as a ‘Trivial Pursuits’ answer, I find that most people aren’t particularly interested and would just rather know if they have them in their house; and if so, what to do about them. However, it is probably best to be aware that this beetle has a three to four year life cycle; and the vast majority of this is spent within the timber, as a grub or larvae: whilst it is in there, munching away, it is not easy to get at!

During that period, it will be eating the timber on a fairly regular basis; at least three square meals a day, often with additional grazing moments, perhaps resulting from boredom at the seldom-changing scenery. As it eats, it behaves like a tunnel boring machine, creating little galleries for itself. Although these tunnels can be visually attractive, they do nothing for the condition of the timber surrounding them.

After a period of time, which is variable but usually in the fourth year of its existence, the larvae pull that wonderful trick that insects are renowned for.  They dig themselves a chamber, go to sleep, and wake up as a beetle, which despite its lineage, does not relish confinement inside a piece of wood. Just as soon as its alarm clock goes off, it makes a dash for fresh air, and to do this it must tunnel its way out of its custody suite.  Being equipped with nothing other than teeth for this purpose, it starts to gnaw, and gnaw, and gnaw.

Eventually, it arrives at the surface, and once there it sets about its next role in life with some gusto. The purpose of the adult beetle is quite specific: it is to find another of the opposite sex, and then to mate.  Once this is successfully done, they shuffle of this mortal coil. However, before doing that, the female of the species lays her eggs, either in cracks in the timber, or in one of the previously constructed exit holes.  From there the cycle stairs all over again.

Neither during their gnawing stage, nor the short but purposeful period after their emancipation, do the beetles eat anything; they haven’t the ability; which is a bit of a handicap to a long and happy life. Instead, they settle for a short and happy variety instead.

However, the beetle’s lack of appetite presents a problem if you have murderous intentions towards them, because they are difficult to poison: strictly ‘nil by mouth’ rules out the use of stomach poisons and waiting with a hammer for them to pop out becomes tedious after a day or two.  Instead, reliance is placed on nerve agents, such as Permethrin, which work simply by coming into contact with the beetle when it emerges.  Depending on the efficiency of the treatment’s application – usually by spraying – some of the poison can also seep into the timber and affect any grubs that are operating near to the surface, although this is rather limited.

Other poisons, designed to soak into the timber, affect the larva’s ability to shed and replace its outer skins.  Other agents, such as Boron salts do not act as eradicants although they do prevent re-infestation.

Thus, treatment can be rather difficult and will usually take up to four years to have a permanent effect.  It can also be seen from the foregoing that any insecticide sprayed onto the timbers will have to last for at least four years; thus careful application is very important.  It’s usually a case of the more you can get on, the likelier the chances of it working.

If you do think you might have woodworm, don’t panic. It isn’t likely that your house will crumble around you and the chances are that any infestation disappeared years ago. I think that out of every hundred examples of infestation that I see, at least ninety-five of them are no longer active.  Either because they’ve already been treated with insecticide, and no one knows because no one has thought to keep a record; or because the insects have simply died out, either through lack of nourishment or because environmental conditions surrounding the timbers they lived in made life untenable for them.

Deciding whether they’re still active is often a matter of judgment: when activity is ongoing, there are usually small sawdust-like trails to be found on the timbers, usually on the vertical faces; it’s known as ‘Frass’ and it doesn’t hang around forever. If the emerging beetle pushed it out of the flight hole last year, general draughts and air currents will probably have dispersed it within twelve months.  So, if you can see it, there’s a good chance the infestation is still active. If all you can see are holes, then the likelihood is it’s ceased. This is particularly so if the edges of the holes look ‘soft’ and the inside of the bores looks dull.  Newly made holes are bright, shiny things, especially when viewed obliquely, using torchlight.

Of course there are more ‘scientific’ ways of checking on the viability: you could paste thin paper over the suspect timber and wait to see if any holes appear in it; or you could start to dig into the timber itself, and arrest any grubs that may be loitering with intent.

However, these methods aren’t used that often because a decision on treatment is usually required quickly: waiting for paper to become beatified is akin to watching paint dry; and digging around in the timber is also rather unsatisfactory.  If you dig in one place, and find nothing, it’s very tempting to think “ah, I’ll have another go over here…” pretty soon you’ve done more damage with your penknife than an entire river of larva could inflict (incidentally, if anyone knows the real collective noun for larva, please e-mail me and let me know).

Spraying with insecticides, especially one of the modern ones, shouldn’t be too hazardous as they’re reputedly very safe; but only go for this option if you’re sure it’s needed. Not only is it expensive, its environmental credentials cannot be absolutely verified.

As with all matters pertaining to the damp and timber industry, do have any suspected infestation checked out by someone who isn’t trying to sell you two gallons of insecticide.  Otherwise the opinion you get might be a little bit grubby!