When little moths cause big havoc

Clothes moth larva feed on natural fibres such as hair, wool, and feathers, rather than the dirt and grime we might associate with unhygienic kitchen areas. This type of build-up is usually found below sofas and other heavy furniture, behind televisions, and inside draws and cupboards used for storing clothes. Larva will cause damage during feeding by actively eating garments, carpets, curtains and other soft furnishings. They will also produce silk threads when feeding that can make the same items look unsightly. Fibres containing wool are most commonly attacked, but hair and feathers are also attractive food stuffs. Coarse hair (such as horse hair) may not be so readily attacked as finer pet hairs or human hair. The dirtier the garment, the better for moth larva, as dirt adds nutrients to fabric fibres.

Warm weather also has a significant effect on how rapidly insects go through their lifecycle, the warmer it is the more rapidly insects will reach a sexually mature stage and produce the next generation. In reality population size is dependent on many factors including food availability and temperature. But we have to consider that food availability is not always related to bad hygiene; a woollen carpet will contain enough food to sustain a significant population of moths.

Clothes moths go through a complete metamorphosis, which means they have four completely different life stages:

  • Egg - A female will lay 40 to 50 eggs in her life time, gluing them to a surface, usually on or very close to a food source. These hatch four to ten days after being laid depending on temperature
  • Larva - This is the growing stage when larva feed and cause the most damage. The larval stage will typically last a month but can take up to two years depending on the temperature and the quality of food
  • Pupa - This stage will last from 10 to 50 days depending on temperature
  • Adult – Adults do not feed and will only survive for a few days. The overriding need for the adult is to breed

In summary, the complete moth lifecycle can, on average take from four to six months, but in heated buildings they are able to breed all year round, and produce two generations per annum.

Expensive artefact's, furniture and garments can be fumigated in specialist bubbles using phosphine gas or controlled atmosphere technology such as CO2 or Nitrogen. Less delicate items can be treated using a controlled heating system (Entotherm heat pod) working on the basis that all life stages will be killed after an hour of exposure to temperatures of 55oC. Freezing garment can also be effective but care needs to be taken to make sure that they stay cold for long enough to be effective. It will not be possible to use controlled atmosphere technology or phosphine fumigation on entire buildings if the infestation is present in carpets. It is recommended that conventional insecticide treatments are applied in these situations.

The most eco-friendly approach to control and prevention is careful cleaning. Pull out sofas and thoroughly vacuum beneath them, store woollen garments in clean drawers, preferably inside polythene bags, and refrain from storing carpet ends in dark areas such as attics.