What exactly is woodworm and what can be done to eradicate it?
by David Morton, Senior Surveyor, CSSW, CSRT
Some of the questions we are asked, with regards to woodworm, or wood-boring insects are:
- What is woodworm, or wood-boring insects?
- How do we treat and eradicate a woodworm infestation?
- How to tell if woodworm is active?
- Should I buy a house with woodworm?
- What causes woodworm?
Firstly, the generic term – woodworm – relates to the larval stage of many species of wood boring insects. The initial attack is made when an adult beetle lays eggs, usually on the surfaces of rough sawn timbers. The resulting larvae will then begin to bore into the wood in search of cellulose to feed on.
When the time is ready, the larvae will create a pupal chamber within the wood, just beneath the surface, in which an adult beetle will emerge after metamorphosis. The new adult will continue to tunnel through to the surface of the wood in an attempt to exit, which creates the visible flight (exit) hole. The adult will then seek to mate and start the whole process once more. The life-cycle and visible flight / exit holes varies considerably from insect to insect. The tunnels and chambers that have been created during this process may lead to structural weakening of the affected timbers.
There are five types of woodworm beetles we come across
COMMON FURNITURE BEETLE (ANOBIUM PUNCTATUM)
By far the most common of all insects that attack seasoned timber.
The adult beetle lays its eggs, between 20-80, in crevices in the timber.
Hatching occurs in 3-4 weeks, the grub burrowing into the timber for between 2-3 years.
Normally emergence through the surface of the wood occurs between May and August when the adult beetle creates and exits through the characteristic flight hole.
WOOD BORING WEEVIL (EUOPHRYUM CONFINE)
This is probably now the 2nd most common wood-boring insect we come across. Generally, for an infestation by these insects, the timber is likely to be affected by damp and often fungal decay; usually Wet Rot.
The most common areas likely to be affected are the undersides of ground floor suspended timber floor timbers, such as timber wall-plates, joist ends built into damp affected walls, floor board ends in contact with damp affected walls and the backs of skirting boards where damp is present.
HOUSE LONGHORN BEETLE (HYLOTRUPES BAJULUS)
Originating on the continent this insect has now become endemic in certain parts of Southern England, mainly in Camberley and Walton-on-Thames.
The danger in infestations by this insect lies in its relatively large size, the grub growing to almost an inch in length.
As the life-cycle can be as long as eight years, it is not long before structural weakening occurs.
The other problem is that there may be very few flight, or exit holes visible, but! extensive structural damage can be caused within the structure of the timber which leaves just a thin surface veneer.
DEATH WATCH BEETLE (XESTOBIUM RUFOVILLOSUM)
Death Watch Beetle normally attacks fungally decayed hardwoods, which means it is most often found in the structural timber beams in timber framed (Tudor type) properties. Although it starts in fungally decayed hardwood timbers, the insect can then spread to sound adjoining timber.
There are many ideas on how the insect got its name; one old superstition being that in olden times, people performing a deathbed vigil, known as being ‘on watch’, would hear the clicking noise that the Deathwatch Beetle makes and believed that sound (and the beetle) to be an omen of death.
This insect can cause extensive structural damage and is particularly difficult to treat, without further follow-up treatments due to the very long life-cycle and “post emergence” period.
BARK BORER (ERNOBIUS MOLLIS)
This insect is a relative of the Common Furniture Beetle Anobium punctatum. They share a love of wood, but! where Bark Borer is concerned, the damage is purely cosmetic – it will not cause any structural damage to the timber.
This insect affects the bark of the growing tree. Evidence (flight / exit holes) can sometimes be seen on the wany edges of rafters and purlins within roof voids.
It is important this is correctly identified because treatment against this insect is not necessary.
Treating a woodworm infestation
An important part of how we treat a Woodworm infestation is correct diagnosis because how we treat an infestation varies from insect to insect and also, the extent of an infestation.
Our Surveyors will identify the type of infestation present and will specify the appropriate treatment to the affected areas. In some cases where timber has been structurally weakened, replacement with pre-treated timber may be necessary.
Common Furniture Beetle can usually be treated using an insecticide product applied by spraying onto the surfaces of the affected and adjoining timbers. Timbers of suspended ground floor structures, or roof structures are often covered in dust and cobwebs, so it is also important to clean down – by brushing – the timber before applying the insecticide.
Wood-boring Weevil infestations will often involve cutting out and replacing (with pre-treated timber) any damp and fungally decayed floor timbers. Doing this will generally remove the timber affected by this insect as well. However, we would also treat, by surface spraying with insecticide, adjoining floor timbers to ensure the infestation does not spread to timbers which appear sound.
House Longhorn beetles are particularly difficult to treat due to the long life-cycle, size of the insect and extensive damage which can be done before visible evidence of the beetle is seen. Affected timbers must be adzed, to remove structurally damaged timbers. It is likely some of the affected timbers may need to be either replaced, or strengthened. Sound, adjoining timbers should be treated properly with wood preservative / insecticide to prevent further infestation.
Death Watch beetle treatment is likely to involve removing and replacing damp, or fungally decayed timber along with treatments using both a fungicide and insecticide solution. One of the significant problems in treating timbers affected by Death Watch beetle is that it is normally going to be large sectioned, hardwood beams; such as timber framing, vertical and horizontal structural beams, tie beams etc. in timber framed properties. Because it is hardwood, penetration into the surface of the timber by spraying is likely to be minimal and not effective. Therefore, it is often necessary to use a deeper penetrating preservative paste or gel.
The other problem we have to consider is whether or not the exposed timber beams have been painted, or waxed, which is often the case. In these instances, surface treatment is not likely, unless the surface treatments (paint or wax etc.) can be removed first. Sometimes, because of the long post emergence period, which is the time after initial treatments that beetles will continue to emerge, follow-up treatments may need to be considered and quoted for as part of the treatment specification.
What causes woodworm infestations?
There are a number of reasons woodworm infestations can occur. One of the typical causes is a high, or raised moisture content in the timber. Predominantly sought after by adult female beetles in summer months, so that eggs can be laid. The larvae then burrow, and when it exits, after causing damage by tunnelling through the wood, leaves behind the flight / exit holes you commonly see.
Should I buy a house with woodworm?
If the woodworm infestation is minor and can be easily treated, it may not necessarily be a problem, as structural damage (to the affected timber) may not have been caused. However, if the infestation is severe and has caused significant damage to the structure, it may be best to reconsider the purchase, or negotiate a lower price to reflect the cost of repairs and treatment. In the end, it is not really a question we can answer, because it depends how much you may want the property, regardless of the treatments which may be necessary.
Is the woodworm active?
This is what we have to ascertain following inspection of the affected timbers. One thing to always remember is that after an infection, which may have already been treated, is that the holes made by beetles will still be there. Just the fact that holes are visible does not mean further treatment is necessary. It is important to look carefully at the visible holes. If they are all, or mostly covered in dust and cobwebs, they are probably going to be old holes from an historic infestation. In which case, and in compliance with COSHH (Control of Substances Hazardous to Health) regulations, further treatment with insecticide should not be specified. However, if there are visible holes which a re very “clean”, or where there are small piles of “frass” or bore-dust around them, it is likely that the infestation will be a new and active one.
If you have an infestation by woodworm and would like to arrange for a survey, or would like to speak to one of our Surveyors, please contact us on:
Tel: 01276 66466