Cloth Moth Infestation at Oxford Colleges

EBS Ltd was asked to investigate a clothes moth infestation (the common or webbing clothes moth, Tineola bisselliella) in Oxford colleges.

The common or webbing clothes moth belongs to the order Lepidopteraand family Tineidae.  The flying adults hide in dark areas and shun the light.  They lay batches of up to 100 eggs on fur, feathers, skins, wool or soiled silk.  Therefore any items in the property made up of these will be at risk of infestation and deterioration.

Adult clothes moths are small, dull, grey/fawn moths, about 5-8mm long. The common or webbing clothes moth has more of a golden sheen, compared to the case bearing clothes moth Tinea pellionella, which is more greyish.

The moths scuttle around and only fly when it is warm.  Normally they fold their wings along their back when at rest.  The head is rather roughly haired, with the proboscis (or feeding tube) reduced or absent altogether.  

Hence, the adult insects do not feed and it is their larvae (or caterpillars) that damage our fabric.  Clothes moths in general are dark-loving insects and, although males and spent females sometimes come to light, they are more likely to scuttle for cover than to fly into the open when disturbed.

Moths of both species can fly in through open windows or doors and can also come from birds' nests in chimney flues or roof eaves.  One generation normally takes a year to develop but there are often two generations a year in heated buildings.  The larvae, which hatch from the eggs, spin silk webbing.

The larvae are whitish in colour and feed mainly on dried plant and animal material.  Clothes moth larvae are among the few insects able to digest the keratin of hairs and feathers.  The natural haunts of these insects are the nests of birds and small mammals, from where it is only a short step to human households in which carpets, clothing and general debris provide abundant food.  Damage to articles may consist of irregular surface feeding (especially on carpets) or holes eaten completely through the fabric, usually in association with the 'tell-tale' signs of silk webbing produced by the caterpillars.

The highest numbers of flying clothes moths were found in and around the central staircases at all levels.  To a lesser degree active clothes moths were also found in the entrance areas, landings, rooms and cupboards.

It was suspected that the moths were living in wool insulation used in the building or in adjacent college buildings.

In the squash courts a strip of Marmoleum was lifted in the basement to check for clothes moths infestation. Cloth moths’ webbing was found on the woven jute backing and active larvae were found in the webbing (see photograph below showing moth webbing activity under Marmoleum).

Showing moth webbing activity under Marmoleum.

The edges of the Marmoleum were inspected in the basement/ground floor staircase and clothes moths’ webbing was found on the woven jute backing.

Wool insulation is very fashionable as an environmentally friendly product but if it has not been treated adequately, it is a good food source for the larvae of the webbing clothes moth Tineola bisselliella. 

A thorough inspection of infested buildings was carried out using a Borescope to find all sources of infestation before making any attempt at control.  Correct identification of the infestation is the key to success.  It is important to remember that the adults of these insects do not feed on materials that may be attacked by the larvae.  Clothes moths larvae prefer to feed in hidden, secluded and protected places.  

No materials were found which would provide a food source for the moths and it was concluded that the moths were entering the buildings’ common areas through open windows (during the warm summer months) possibly fromadjacent buildings, which were infested.  Enquiries revealed that adjacent Oxford college buildings had been affected in the past and had been treated to kill the moths. It was concluded that this had not been entirely successful.

Keeping the windows closed was an easy solution to this problem whilst the source of the moths was investigated.

A variety of monitoring traps are available to catch flying insects.  Much can be done to prevent clothes moths problems by means of household cleanliness, including thorough and frequent cleaning of carpeting and upholstery with a vacuum cleaner and brushing, airing, and dry cleaning of susceptible clothing or other articles.  Removal of the infested reservoirs and treatment of the infested material is very important to control clothes moths.  Rarely, some targeted chemical treatments may be needed.