Carpet Beetles and Clothes Moths

What they are, what they eat and how to control them

Robert Child and David Pinniger

 

   
  Figure 1 Webbing clothes moth adult
(All photos: David Pinniger/CSL/Collections Trust)  
 

There are two main types of insect which cause serious damage to textiles in the British Isles: clothes moths and carpet beetles. Although very different in appearance and habits, both are pests which eat animal fibres such as wool carpets and cashmere or mohair clothing.

CLOTHES MOTHS

The common or webbing clothes moth (Tineola bisselliella) and the case-bearing or case-making clothes moth (Tinea pellionella) are the two main pest species. Both will attack and damage carpets, upholstery, clothing and animal specimens. The common or webbing clothes moth is now the most common species and has become a much more marked problem in recent years.

The adults of both species are small, dull, grey-fawn moths which are 58mm long and look quite similar. The common or webbing clothes moth (Figure 1) has more of a golden sheen, while the case-bearing clothes moth is more silvery-grey (Figure 5). They scuttle around or fly when it is warm and fold their wings along their backs at rest. Case-bearing clothes moths often come from birds’ nests, particularly in unused chimneys, and can fly in through windows or open doors. One generation normally takes a year to develop, but webbing clothes moths can reproduce rapidly in heated buildings with two generations or more per year.

The adults avoid light and lay batches of up to 100 eggs in dark areas on fur, feathers, skin, wool or soiled silk. The larvae, which cause the damage, hatch from the eggs and spin silk webbing as they feed and grow.

The common or webbing clothes moth The larvae of this species spin silk as tubes or sheets of webbing across the material they are eating (Figure 2). Damage is accompanied by copious webbing tubes which usually include large amounts of excreta known as frass (Figure 3).

The case-bearing or case-making clothes moth The larva spins a case or bag around itself, leaving the ends open so that it can use its jaws and legs (Figure 4). It then eats as it crosses the material carrying its case and leaving a trail of grazed textile or fur with fragments of excreta or frass. The larva moults within the case and when fully grown it pupates within the cocoon and eventually the adult moth emerges to mate and lay eggs. Infested material is often littered with empty silk bags or cases (Figure 6) which resemble grains of rice.

From left to right: Figure 2 Webbing clothes moth larvae; Figure 3 Frass and damage caused by webbing clothes moth larvae; Figure 4 Case-bearing clothes moth larva in case; Figure 5 Case-bearing clothes moth adult

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

Textiles soiled with food, perspiration or urine are preferentially attacked and a stained area may be more damaged than an adjacent clean one. Damage is also more concentrated in dark and hidden areas so that in clothing, for example, it is likely to occur in crevices and creases, behind lapels, in pockets or where things are folded. In carpets, clothes moths will usually be found under heavy furniture or at the undisturbed edges. Clean, cotton materials are not normally at risk from attack by clothes moths but the larvae will eat holes in the cotton coverings of feather cushions if the fillings are infested.

OTHER MOTH SPECIES

   
  Figure 6 Empty moth cases on upholstery  

Other common moth species which can be confused with the clothes moth are the white-shouldered house moth (Endrosis sarcitrella) and the brown house moth (Hofmannophila pseudospretella). Both of these species are common in birds’ nests and will only cause damage to materials stored in damp and dirty conditions. The Indian meal moth (Plodia interpunctella) is commonly found in domestic kitchens, but this species will only attack food such as cereals, nuts and dried pet foot.

CARPET BEETLES

The most damaging species of carpet beetle found in the British Isles is the varied carpet beetle (Anthrenus verbasci). Adult beetles are 2-3mm long and resemble small ladybirds. They are covered with grey and gold scales (Figure 8) and identification of the species is based on the pattern and shape of these scales. Adult beetles fly well in warm weather and may frequently be found on windowsills. In the British Isles they are found outside in later spring and early summer where they mate on flowers such as hogweed and Spirea before they return indoors to lay batches of eggs secreted in cracks and crevices.

The eggs hatch into short, fat, hairy larvae, often referred to as ‘woolly bears’ (Figure 9). When the larvae first hatch they are extremely small, less than 1mm long, and they can gain entry to cupboards and drawers through very small cracks. As the larvae grow, they leave empty hairy, cast skins or husks which are often the first sign of carpet beetle attack (Figure 7).

   
  Figure 7 Cast skins of varied carpet beetle larvae  

The larvae will grow to 5mm long and are voracious feeders which will rapidly make holes in woollen textiles, animal specimens, fur and feathers. They will also graze on animal glue in book bindings and picture frames. Clean cotton materials are not normally attacked although larvae may bore through them on their way out of a feather cushion. The damage is often mistaken for clothes moth larvae attack.

Carpet beetles are often found in natural situations such as birds’ nests, wasps’ nests and animal burrows and in some museums and houses they have a direct route into the premises from nests in attics and chimneys. Once established, they can be difficult to eradicate because the larvae can forage widely and may take some years to complete development. The normal life cycle is one to two years.

There are other species of Anthrenus which are similar in appearance and habits. The most important of these is the Guernsey carpet beetle (Anthrenus sarnicus). This is now well established in London and South East England and is causing increasing problems in the rest of the British Isles in houses and museum collections.

PREVENTION

Clothes moths and carpet beetles are frequently found in birds’ nests and discarded animal-based textiles, such as old carpets and underlays in loft areas. The long-term solution to infestations is to make sure that birds’ nests are removed from attics and particularly from disused chimneys. This should be done after any nesting period has been completed. Roof spaces should be cleared and cleaned and any suspect material removed and destroyed.

Good housekeeping, through regular cleaning, is the long term method of control of insect attack in buildings. Good design that allows inspection and cleaning of all areas is also to be encouraged. Regular vacuuming of carpets is essential, particularly along skirtings and under furniture. Wool-based clothing should be put into storage after being dry cleaned or warm washed as clothes moths prefer soiled material to clean.

MONITORING

Early detection of insect attack obviously helps minimise any damage and allows a swift response to the infestation. Insect traps can be valuable in catching flying and crawling insects, allowing them to be identified and the severity of the attack assessed. Sticky blunder traps are the most successful at catching a wide range of insect pests, as many insects such as clothes moths are not attracted to light or ultraviolet traps.

Where the insect species is known accurately, pheromone traps can be used. These are sticky traps which use the female sex pheromone of the species to attract males. They are commonly used for webbing clothes moth but are also available for case-bearing clothes moth and some carpet beetle species. Although very efficient, they should only be used as an enhanced trapping system, not a control measure.

TREATMENTS

Where some form of insecticidal treatment is necessary, the problem needs to be assessed in terms of the efficacy of the treatment, possible adverse effects on the inhabitants of the property and possible damage to objects through staining, etc.

   
  Figure 8 Adult varied carpet beetle Figure 9 Varied carpet beetle larva or ‘woolly bear’  

Recent changes in legislation through the Biocides Directive (European Union Directive 98/8/EC) are having an effect on the treatments and materials that can be used. Many traditional insecticides such as mothballs are now banned and others are likely to follow. Museums and historic houses are increasingly using non-toxic treatments such as deep freezing and heat. Sealing infested carpets or wool clothing in plastic bags and freezing them at -18°C for two weeks will kill all stages of insect life. Heating objects to 55°C+ will kill all insect stages in an hour but great caution must be taken to ensure the objects are not damaged by the very dry hot air. The Thermo Lignum heat process uses heat and controlled humidity in a chamber to avoid damaging objects.

Domestic treatments include the use of residual sprays containing insecticide such as permethrin around the edges of carpets, under furniture and in other vulnerable areas. Hanging sachets which give off an insecticidal vapour can be used in enclosed spaces such as drawers and wardrobes. Commercial treatments can include the use of insecticidal smoke generators or ‘fogging’ with an ultra-low volume insecticide. Although these have value in killing adult moths, they do not penetrate into the textiles. Targeted use of Exosex, a pheromone-based system that disrupts moth mating, can be effective in reducing moth numbers in large, difficult to treat buildings.

CONCLUSION

With fewer cold winters and more warm, centrally heated buildings, clothes moths and carpet beetles are becoming an increasing problem with faster breeding cycles. More insects per year are produced and the warmer conditions allow them to fly or crawl further and higher, spreading infestations into areas not previously attacked.

Prevent moths and beetles causing damage by:

  • good housekeeping, particularly in dark and undisturbed areas
  • regularly checking stored vulnerable materials
  • monitoring with insect traps
  • ensuring pests are correctly identified
  • using targeted treatments against insect infestations when they occur.

 

~~~

Recommended Reading

  • DB Pinniger, Pest Management in Museums, Archives and Historic Houses, Archetype Publications, London, 2001
  • DB Pinniger, Pest Management: A Practical Guide, Collections Trust, London, 2008

 

 

 

The Building Conservation Directory, 2012

Author

ROBERT CHILD is a former head of conservation at the National Museum of Wales where he specialised in preventive conservation of historic collections. He is the National Trust’s advisor on insect pest control and has his own insect pest consultancy, Historyonics.

DAVID PINNIGER is an entomologist who advises English Heritage and many museums and historic houses on pest identification and pest management.

Further information

RELATED ARTICLES

Damp and Decay

Pests

 

RELATED PRODUCTS AND SERVICES

Damp and decay specialists

Damp and decay treatment products

Environmental control

Insect and pest eradication

Non-destructive investigations

Surveyors

 

BuildingConservation.com
Site Map

© Cathedral Communications Limited 2012