Insect attack to timber Introduction Understanding the life cycle From earliest times timber has been used of -boring as a component of traditional buildings When dealing with an infestation it is in Scotland. It can be found in almost important to have an understanding of all elements including floors, walls, the life cycle of wood-boring insects. windows, doors and roofs. A variety of The three stages of development of these factors can lead to its break down and insects are: decay, including attack by pests. Insect attack to wood is a problem • An egg, which is laid in timber which causes considerable concern in • A larvae, which feeds on timber the mind of building owners, and is • A winged insect which emerges from also one of the least understood decay the timber to lay further eggs mechanisms which can affect timber. This INFORM seeks to guide building It is not the insect in its winged state owners through identification of an which causes damage but rather the insect problem, and how best to end larvae which feeds on timber before such an attack in a safe, effective and emerging in this winged state. The economic manner. holes which can be seen in timber following attack by insects are the flight holes caused by the winged insect emerging. Larvae can exist in wood for up to 10 years, it is therefore vital when considering treatment options to target not only the winged insect but the larvae and eggs which will thrive in timber as long as conditions are conducive. The most effective long term cure is to remove the conditions which allow egg, larvae and insect to survive.

Identifying the insect As there are a number of insects which can attack wood correct identification of which is present will assist its proper eradication. The following are the most likely insects to damage timber:

Fig 1: Wood damaged by furniture Fig. 2: Bore dust of the common furniture beetle Fig. 3: A common furniture beetle (measuring 0.5 cms long) Common furniture beetle Death watch beetle Commonly known as woodworm, the This beetle is uncommon in Scotland common furniture beetle is the most likely but can still be found on occasion. This insect to threaten timber in Scotland. species can be identified by the larger The beetle can be identified by the round holes which they leave in timber (around holes which they produce in timber and 3mm in diameter). It attacks wood that the egg shaped pellets of bore dust they has experienced some form of decay or rot leave. The damage is caused by the larvae in the past. As with the furniture beetle, that, after hatching, bore into wood in it is the larvae which cause damage, and search of nutrition. This larval phase can they can exist in that stage for as long as last for up to 3 years, therefore, if left 10 years. They are particularly prone to unchecked, considerable damage can attack built-in sections of timber where be caused to structural timber. Where ventilation is poor and can thus remain moisture content is below 12% it is hard undetected for some time. An extensive for the larvae to survive. Conversely, where infestation can cause structural failure in moisture content is high, and especially timber. where rot has already occurred, timber is particularly vulnerable to attack. Sapwood Wood-boring weevil (the outer section) of soft wood trees such Wood-boring weevils attack damp timbers as spruce and fir is especially prone to especially where they are also suffering infestation. A serious outbreak of furniture from decay. It is important not to mistake beetle larvae can cause severe damage and wood-boring weevils for common furniture when coupled with rot, could well require . The holes made by weevils are oval replacement of timbers. shaped (as opposed to the round holes of the furniture beetle) with finer bore dust. Once moisture is removed from wood, and any decay dealt with, the weevil infestation will cease without the need to resort to the use of chemicals. This principle largely applies to all insect infestation.

Powder post beetle These beetles most commonly attack new timber, hardwoods and building elements such as flooring. It can also attack existing building elements if the conditions are right. It produces a very fine bore dust, Fig. 4 and holes around 2mm in diameter.

Treatment of insect attack There are two main ways of eradicating an insect pest: environmental control and chemical treatment. Allied to both are various post treatment actions which should be carried out once the pest is eradicated.

Environmental control As with rot, the most effective long-term strategy when dealing with an attack is to remove the conditions which allow the insects to thrive in the first place. The easiest way of making such a change is to Fig. 5 reduce the moisture content of the timber and the area adjacent to it. This can be achieved in a number of ways including the introduction or reinstatement of ventilation, removal of sources of moisture such as defective gutters, leaky roofs or pipes and in some cases artificial drying. A further environmental control is to ensure that any timber which is affected by rot is removed and replaced. Rotten timbers are far more susceptible to insect attack than sound wood. Fig. 6 Figs 4 – 6: The most effective form of treatment of insect attack is the removal of sources of moisture such as defective gutters, leaking pipes or slipped slates. Chemical treatment • You should always ask what chemicals are going to be used and check these Whilst environmental controls are the for any dangers to health such as most effective way of ridding a building skin or eye irritation. If these are of insect pests in the long term, it may likely hazards enquire as to how be necessary to use chemical treatments long the treated area will have to to help eradicate outbreaks in the first remain vacated following treatment. instance and to stop established insect All chemicals being used should be pests causing further damage. There are approved by the Health and Safety several different methods of application. Executive. Whatever method is used it is important to bear the following points in mind: • Ensure water tanks are completely sealed to avoid contamination. • The application must bring the treatment into sufficient contact with Methods of application the insect to ensure that enough are killed to make the colony unviable. Spraying Spraying an agent onto the surface of • If an infestation only affects a localised wood is unlikely to be fully effective area of a building the treatment against some species of pest but will be should be targeted to that area. In more effective against furniture beetle. To most instances insect infestation is a maximise the surface retention of sprayed localised problem therefore large-scale treatments the applicator nozzle should treatment, is unlikely to be required. be kept close to the wood being treated • It is important to identify the species and the chemical dispensed at a relatively of insect being treated to ensure the low pressure. correct treatment is being used. Injection • Ask if the contractor carrying out A more effective method than spraying the work has been properly trained. is injection of the treatment into wood. Although there is no legal requirement This is more likely to ensure that the for this, it is important to ensure that agent penetrates deep enough into the the workforce is competent. timber to kill the majority of insects. It may be necessary to drill small holes in

Fig 7: Timber previously attacked by rot is particularly Fig 8: Replacement of decayed timber vulnerable to insect infestation applications. much lessspecificthaninjectionorspray treatment have thedisadvantage ofbeing may berequired. Bothfoggingandsmoke hard toreach areas andseveral applications be abletoreach theeggswhichare laidin have some limitedsuccessitisunlikelyto designed totargeteggs. Whilst foggingmay treated, thefoggingofchemicaltreatment is Particularly usedwhere largeareas are tobe Fogging therefore unlikelytobeaneffective option. to completelyeradicatethepestandis to berepeated over several years in order timber. Thistreatment willtherefore have withinthe not ineradicatingeggsorlarvae successful againstemergingadultinsects, Smoke treatment isonlylikelytobe Smoke treatment than spraying. chemicals theycontainandbemore effective likely toensure deeperpenetrationofthe The applicationofpastetreatments is Paste to injectthetreatment intotheflightholes. Analternativeafterwards. tothisapproach is alocationaspossible andfilled unobtrusive this isthecasetheseshouldbemadeinas the timbertoensure effectiveness, where While every care hasbeentakenin thepreparationWhile every ofthisleaflet, Historic Scotland specifically exclude anyliabilityforerrors, Published by Historic Scotland,Longmore House, Place, Salisbury Edinburgh EH91SH omissions or otherwise arisingfrom itscontents andreaders mustsatisfythemselvesomissions or otherwise astheprinciples andpracticesdescribed www.historic-scotland.gov.uk email:[email protected] English Heritage Guide, Glasgow West Conservation Trust Guide 7 Ridout B., Further Reading Timber Decay inBuildings Tel: 01316688638Fax: 01316688669 Principal author: Moses Jenkins Insect Pests inHistoric Houses • • • including: to ensure re-infestation doesnotoccur remedial totakecertain actions important After aninfestationhasbeentreated itis Post-treatment actions ISBN0-419-18820-7 It monitoringapreviously isalsoworth Ensure thatanysources ofmoisture Ensure allseverely damagedordecayed chemical treatment mayberequired. controls or limitedapplicationsof environmental of insectactivityfurther completely. If there is continued evidence ensure thatapesthasbeeneradicated affected area aftertreatment to unlikely tobesuccessfulinthelongrun. to cure moisture anddampingress is control without adequateremedial work and makere-infestation lesslikely. Pest improve thegeneralhealthofabuilding, and dampare removed. Thiswillalso insect attacks. is alsomore likelytoencouragefuture integrity ofthebuilding,decayed timber This isnotonlyvitaltomaintainingthe timber isreplaced following treatment. Rot andinsect infestation

APS Group Scotland 179033 (06/11) Produced from sustainable material