With the loss of the traditional ‘spring clean’ in domestic premises where clothing, rugs and textiles would be aired in direct sunlight once a year while the cleaning took place, so the common clothes moth, Tineola bisselliella, has become an increased problem in houses. The ultra violet light from the sun during the spring clean was a natural killer of the larval stage of the moth.
Today, woollen jumpers and cashmere scarves get left in drawers, and woollen carpets have furniture items standing in the same place for years, all creating the perfect habit for textile moths to breed and do damage to natural textiles unnoticed.
The clothes moth, also known as the webbing moth, occurs worldwide with the exception of the tropics. Before the creation of textiles it will have lived in birds nests and the fur and feather of dead animals.
The total life cycle of the clothes moth is between 3-10 months, depending on temperature, following the egg – larva – pupa – adult life cycle. Clothes moths are relatively cold hardy and larvae can survive temperatures down to -15C for several weeks. At temperatures above 10C the eggs will hatch in 1-5 weeks, above 20C within 4-10 days. The eggs are oval and are 0.5 mm long and are ivory in colour. The adult female moth will lay her eggs directly among natural fibres which will be the food stuff for the emerging larva, singly or in small batches, up to 200 eggs in total per adult female.
After hatching, the white newly emerged larvae spin silk from glands located behind the head to form a tubular cocoon, into which they will combine excreta (frass) and other materials from the immediate vicinity, resulting in good camouflage. From the safety of this cocoon the developing larvae will emerge at night to feed on surrounding natural fibres, causing the tell-tale damage for which the species is well known. Around 5 moults will take place as the larvae develop and the silk cocoon will be gradually enlarged accordingly. Poor quality food or sub optimal temperatures can cause up to 45 moultings to take place.
The larval stage can last between two months and several years, depending on environmental conditions.
The final larval moulting will enclose both ends of the cocoon and remain inside the cocoon for development into the pupae. This development can take between two weeks and two months.
The fully formed adult moth then emerges from the pupa. Adult moths do not feed and are generally inactive during the day. Adult moths are relatively sedentary, with only the males occasionally flying for the purpose of locating a female for mating. After the female has laid her eggs she will die within two weeks, with the male moth typically lasting one month. The twelve clothes moths shown in the bottom picture were caught on a pheromone impregneted sticky card which is a useful tool in establishing centres of infestation.
The picture below, you may notice, is a little misleading as it suggests adult moths eating woollen fibres. The adults have no active mouth parts and are simply the reproductive part of the life cycle, but I couldn’t resist the picture!
Modern methods of clothes moth control are varied dependent on the nature and extent of the infestation. Identifying the source of infestation is vital in order to achieve complete eradication. Pheromone impregnated sticky monitors can be used to monitor the progress of the treatment and can also be used to help identify the extent of infestation within a premises. The source of infestation may not always be obvious. The source can be a bird nest in the loft, a fur coat that has been forgotten in a cupboard, or the corner of a wool carpet which gets missed during the routine vacuuming. Large pieces of furniture will need to be moved to ascertain if moths are infesting hidden areas of carpet. Moths can even survive on the pet hairs and fibres which have fallen between floor boards.
Affected garments can be treated with a hot wash in a washing machine, at at least 50C for 20 to 30 minutes. Dry cleaning can also be effective. Where this is not appropriate, it is generally recommended to throw the affected garments away. A professional Pest Controller my choose to knock down adult moths with an insecticidal mist treatment of the affected rooms. This is known as an ‘Ultra Low Volume’ mist treatment. The tiny particles of insecticide generated can permeate and penetrate into all areas if used correctly. However it will not permeate into folded clothing or closed drawers, so it will be important allow good air circulation where needed. There is generally no residuality in this treatment and will only knock down the adult moths present at the time. This will not treat the larval stages of the moth as they are safe in the protection of the silk cocoon. A wet spray treatment, known as a ‘Coarse Spray’ on account of the larger droplet size, can then be deployed to treat carpets and rugs. This will be applied using a straight forward hand held sprayer and will have residuality of up to a couple of months, depending on factors like sunlight degrading the active ingredient, frequency of vacuuming, foot fall and the nature of the surface being treated. Always carry out a thorough vacuuming before treatment rather than after!
As with all insect pests, professional Pest Controllers can use heat treatment to kill all life stages of clothes moth. This involves heating entire rooms up to 60C for at least one hour.
In very sensitive areas such as museums, larvae of the parasitic wasp Trichogramma can be introduced. When the adult wasp develops it lays its eggs in the eggs of the clothes moth, preventing its development into larva. Synthetic pheromones can also be used to confuse the reproduction cycle in the male moths.
Traditional moth balls containing napthaline are still available, despite being banned for sale for moth treatment in Europe since 2008! It was banned due to the carcinogenic nature of the active ingredient. Lavender bags and cedar wood balls have taken their place in the domestic market as moth repellents.
Never underestimate the value of regular vacuuming, storing of only clean garments, and rotating of jumpers and other natural fibre garments.