Ragged Edge - Insect Pests of Textiles

David Pinniger

Insects have been known to damage textiles from earliest times, as illustrated by the biblical reference, "Your clothes are moth eaten", James 5.2 and Aristophanes' immortal report "Moths were eating the feather plumes of helmets" in 400 BC.

Although modern methods of chemical and environmental control have reduced the incidence of pests there is still need for vigilance to ensure that insects are not allowed to breed and damage fabrics and textiles. Carpets, curtains, upholstered furniture and other objects which are most susceptible to attack contain material of animal origin including wool and wool products such as felt, natural animal fur, feathers and hair, and untanned leather and skins.

Although silk can be attacked, serious damage usually only occurs when objects are soiled. Insects will not breed in cotton and so it is not usually damaged although some insects will chew exit holes through cotton covers. Damage to covers can be a particular problem with cushions and upholstery filled with feathers or hair.

The main insect pest species in Great Britain are clothes moths and carpet beetles which are very different in both their appearance and the damage which they cause.

CARPET BEETLES

Figure 1: Adult carpet beetle Anthrenus verbasci on hogweed flower

Figure 2: Woolly bear larvae of the carpet beetle Anthrenus verbasci

The most common species is the varied carpet beetle Anthrenus verbasci, although there are a number of other species of Anthrenus which are similar in appearance and habits including the Guernsey carpet beetle Anthrenus sarnicus, which is now well established in London and causing increasing problems. Adult Anthrenus are small rounded beetles, 23mm long, covered with patterns of grey and gold scales (Figure 1). Adult beetles fly outdoors in late spring and early summer where they mate on flowers before returning indoors and may frequently be found on window sills. The damage is not caused by the adult beetles but by active, short, fat, hairy larvae often referred to as 'woolly bears' (Figure 2). These larvae are voracious feeders and will rapidly demolish fur, feathers and woollen textiles. As they grow they moult and leave empty cast skins which may be the first signs of beetle attack. Carpet beetles can be found in natural situations such as birds' nests and in some houses they have a direct route into the premises from birds' nests in attics and chimneys.

CLOTHES MOTHS
Two species of moth will attack and damage textiles - the case-bearing clothes moth, Tinea pellionella, and the common or webbing clothes moth, Tineola bisselliella. The adults are small, dull, grey-fawn moths 5-7 mm long, which scuttle around rather than fly and when at rest fold their wings along their back. Moths hide in dark areas, shun the light and lay batches of eggs on fur, feathers, skins, wool or soiled silk. The larvae which hatch from the eggs spin silk webbing. The case-bearing clothes moth larva, Tinea, spins a cocoon around itself leaving the front end open so that it can use its jaws and legs (Figure 3). It then eats as it crosses the material carrying its case and leaving a trail of grazed textile or fur with some fragments of excreta or 'frass'. The larva moults within the case and when fully grown it pupates within the cocoon. Eventually the adult moth emerges to mate and lay eggs.

Figure 3: Larvae of the webbing clothes moth Tinea bisselliella and damaged fabric

The common or webbing clothes moth, Tineola, has different habits; although the larva also spins silk it leaves this as a tunnel or sheet of webbing across the attacked material under which it grazes. Damage by this species is accompanied by copious webbing tubes or sheets which frequently include large amounts of frass, and infestations appear far more 'messy' than the damage caused by Tinea. Adult moths can fly in through windows or open doors and can also originate from birds' nests. One generation normally takes a year but development can be rapid if local conditions are suitable. Damage is also more concentrated in dark areas and crevices or creases, for example under furniture and cushions or where carpets or textiles are folded.

The pelleted excreta or frass produced by the larvae of clothes moths is frequently mistaken for moth eggs. However, frass pellets are hard and opaque whereas moth eggs are very small and translucent and vulnerable to physical damage. Contrary to popular opinion, eggs will not remain dormant in textiles and then hatch many months later.

GENERAL DETRITUS FEEDERS, MOULD FEEDERS AND SCAVENGERS
There are very many insect types and species in this group including the Australian spider beetle Ptinus tectus, booklice Liposcelis bostrychophilus and silverfish Lepisma saccharina. These insects generally cause only nuisance and low levels of damage but occasionally localised, humid environmental conditions encourage insect populations to build up to levels sufficient to cause serious damage.

WHERE DO INSECTS COME FROM?
Insects cannot be spontaneously generated in objects and it follows that, if infestation develops it must have been acquired from some other source. The most obvious way for insects to gain access to houses is through doors and windows from the outside world. Carpet beetles fly readily in warm summer months and even one fertilised female can lay sufficient eggs to start an infestation. In general, the warmer the weather, the greater the risk from invasion. Birds' nests and dead animals in attics are the natural home of many pests where they live quite happily on feathers, hairs and excreta. When insect numbers exceed the food available they will spread out in search of other breeding sites in the house. Some pests will live in a house for many years at low levels without apparently causing a problem and it is not until all the conditions are right that serious damage occurs.

PEST PREVENTION
A successful strategy for pest prevention depends upon the integration of inspection, exclusion and environmental control. Good cleaning standards are essential because pests thrive in a dirty, undisturbed environment. Debris and rubbish provide shelter from detection as well as food. With regard to the building environment there should be no compromise; all areas should be kept as clean as possible.

Insects can be introduced on objects and textiles which are already infested and if the insects remain undetected then a serious problem may develop. Visual inspection supplemented by the use of sticky monitoring traps will provide early warning of insect presence and may allow a potential problem to be identified before serious damage can occur.

CONTROL
What happens when insects are found? A panic-stricken grab for the nearest can of insecticide is not the answer. A rational and carefully considered reaction is required when the following questions are answered:

•Is the insect a pest or a non-pest?
•Is the insect alive or dead?
•Are there many insects or very few?
•Are the insects widespread or restricted to one area or object?
•Is there damage to objects?
•Are there other objects at risk in the area?
•Can the object or area be isolated or removed?

If it is decided that control measures must be applied then it is important to choose the most appropriate course. Effective control of the insects can be achieved in a number of ways including physical and chemical methods.

Selective application of the correct insecticide formulation to potential breeding sites in the building may be useful but most residual and aerosol insecticides which are sold for use in household situations are rarely effective or appropriate for use on infested objects. If inspection of objects shows that remedial treatment is necessary to control infestation then it is important to consider the range of options which are now available. These include fumigation treatment with a gas such as the insecticide methyl bromide, or the atmospheric gases carbon dioxide or nitrogen. In most cases such treatment will have to be carried out either off-site in a special chamber or on-site in a bag or 'bubble' enclosure. It is also possible to kill insects with extremes of temperature under controlled conditions which avoid damage to objects. The use of a freezer to reduce temperatures to -30°C has been successfully used to treat textiles but it requires a very careful regime of handling and enclosing objects in bags. High temperatures of 55°C can also be used to kill insects when combined with close control of humidity as used in the Thermo Lignum treatment.

The choice of the most appropriate and correct response will depend upon a number of factors and it is usually advisable to get expert advice. This may not only prevent further damage but also may avoid unnecessary and expensive remedial treatments.

FURTHER READING
Child, RE and Pinniger, DB, Insect Trapping in Museums and Historic Houses. Proceedings, International Institute of Conservation, 15th International Congress, Ottawa, 1994.
Daniel, V and Hanlon, G, Non Toxic Methods for Pest Control in Museums. Proceedings, 3rd International Conference, Biodeterioration of Cultural Property, Bangkok, Thailand. 1994.
Hillyer, L and Blyth, V, Carpet Beetle, a Pilot Study in Detection and Control. The Conservator 16. 1992
Mourier, H and Winding, O, Collins' Guide to Wildlife in the House and Home. Collins, UK. 1986.
Pinniger, DB, Insect Control with the Thermo Lignum Treatment. Museums Journal. 1996
Pinniger, DB, Insect Pests in Museums. Archetype Press, London, UK. 1994.