Life Cycle & Description
Description of Common
Moderately common pest of animal derived fabrics, furs and feather products. Found worldwide except tropics. Damage by larval stage only.
Egg – larva – pupa – adult.
Total life cycle about 3–10 months.
Eggs – in suitable larval food, among clothing or carpet fibres.
Hatch above 10 °C in 1–5 weeks.
Larvae - whitish caterpillars that form silk tunnels camouflaged with fibres and debris. Leave tunnels at night to feed, hide during day. Develop in 2–7 months.
Pupae - inside last larval skin concealed in fabric. Develop in 2 weeks to 2 months.
Adults - small, straw coloured fringed wings held along body when at rest. Females do not fly, males occasionally. Do not feed, short lived.
Pest of museums, domestic fabrics but less common than formerly.
Good hygiene, residual sprays, ULV Fogging
Distribution and Habitat
An indoor insect common throughout Britain and most of the world, with the exception of the tropics. Reasonably cold-hardy and associated with many natural products of animal origin, especially woven fibres, fur and feather products and fertilisers. Despite these food preferences, this species is not a frequent inhabitant of birds' nests.
The mated, adult female moth tries deliberately to lay her eggs amongst fibres of a suitable food material for the larvae. The larvae will emerge at temperatures above 10oC, and almost immediately start to spin silk from glands situated below the head. Sometimes the silk forms a mat or tent, but more usually each larva constructs a smooth-lined tunnel by weaving the silk in amongst excreta (frass) and particles of substrate. The resultant camouflaged case, with periodic enlargement, serves as a home throughout the larval development period, the caterpillar emerging at night to feed and returning to the safety of its tunnel during the day. A normal number of five moults occur prior to pupation, but poor-quality food materials and low temperatures can extend the number of moultings up to as many as 40. The pupa is formed inside the final larval case, and remains concealed until shortly before the emergence of the adult moth. Then the fully formed adult within the pupal case wriggles free of the silk tunnel and emerges.
The female moth is quite sedentary, but the males do fly on occasions. It is the male that exhibits most excitement in the pre-mating action, but in most other circumstances both sexes move by running or occasionally jumping. It is characteristic of this species for the adults to be seen "scuttling'’ in and amongst the larval food material. The adults are unable to feed, having greatly reduced mouthparts, and without the coiled sucking proboscis of the larger Lepidoptera .
The breeding temperature range is from around 10 to 33 °C, and around 70% humidity seems ideal for this species. Mainly depending on temperature, periods of development can range from one to five weeks for the eggs, two to seven months for the larvae and one and a half to seven weeks for the pupal stage. The quality of food material has an effect on development period and the size of the resultant adult moths.
At one time the common clothes moth was by far the most economically important clothing and household pest in Britain, with an estimate in 1948 of £12m of damage caused by this one species alone. It has declined in frequency of occurrence, and severity of damage, possibly as a result of a move away from fibres and furs of natural animal origin to synthetic fabrics. Other species of insects have filled the gap, particularly the carpet beetle and fur beetle (Anthrenus spp. and Attagenus spp.). It occasionally occurs in food storage premises and is able to survive and successfully infest some dried vegetable materials.
Good hygiene is essential and the use of a vacuum cleaner to remove the larvae and their cases will greatly assist control measures. Photo-stable pyrethroids can be used to control larvae not removed by vacuuming. If there are valuable fabrics at risk then the use of pheromone traps can detect the early presence of adults.
The case-bearing clothes moth (Tinaea pellionella) is a species similar in appearance to the common clothes moth, with the larvae feeding on particles of woollen clothing, furniture fillings, furs and carpets, primarily of natural animal origin. The larvae spin a silken case around themselves, often incorporating part of the food material. The case is carried around when the larvae move and damage is solely by eating with no significant silk webbing contamination but some frass. There is normally only one generation per year, although the adult moths may be present in early summer and early autumn.
Description of Warehouse
Temperate species, widespread in UK. Indoors only in warehouses, food factories and shops on wide range of stored food. Sometimes on surface of stored grain. Damage by larvae only.
Egg – larva – pupa – adult. Usually one generation per year.
Eggs – whitish up to 200 per female on larval food over 2 week period. Larvae – caterpillar, whitish with brown head. Forms silk sheets on surface of food. Develop in 2–4 months with 5–6 moults. In autumn larvae migrate upwards on structure of food store. Most enter diapause (resting stage) to overwinter. A few pupate immediately.
Pupae – on structure in silk cocoon in autumn or, more usually, the following sprIng .
Adults – 8–1 C)mm long, greyish wings. Rest on structure when not flying. May fly between adjacent buildings. Appear in early summer and also sometimes in autumn.
Significant stored food pest causing contamination by silk and frass (droppings), and some direct damage. Related species also important (see text).
Monitor with pheromone traps. Residual sprays on structure at appropriate time to kill resting adults or migrating larvae. Pyrethrin or pyrethroid space spray / mist to knock down adults. Larvae in foodstuffs by fumigation.
Distribution and Habitat
Common throughout temperate regions, the warehouse moth is apparently absent from the tropics. It is widespread in the UK. It is an indoor insect that thrives in protected environments such as warehouses, food factories and shops. Most stored food materials (animal and human) will be attacked, although white flour is not attractive to the larvae.
The emergence of adult moths starts in the spring and continues through to autumn, with the male moths flying in response to the pheromones released by the waiting females. Mating usually takes place on stacks of foodstuff, with the mated females laying up to 200 eggs over a two week period. Although the small larvae will easily penetrate most bagged and some bulk food stocks (and even well-sealed packages), the larger larvae tend to move towards the
surface of the food material, and it is here that their habit of trailing thin strands of silk becomes obvious. Heavily infested foodstuffs will be covered with sheets of larval silk hanging in festoons from the edges of the stacks. After five or six moults the larvae are fully grown in the autumn, and they gradually migrate away from their food source and up the walls of the store.
They usually stop at the first ceiling intersection, spinning a silk cocoon well attached to the structure. Only a small proportion of every population pupates immediately, the rest spending the winter months in a resting state called diapause. For these larvae late winter or spring pupation occurs giving rise to the extended adult emergence period mentioned above.
The warehouse moth can withstand very low relative humidities (down to 30%), but is susceptible to low temperatures. It will only survive in unheated buildings in the winter if temperatures inside the larval food material do not fall below 10 °C.
This is the commonest and most serious moth pest of food storage in the UK. Although physical damage caused by the moth larvae can be considerable, contamination is usually far more important. The silk produced by the larvae is difficult to remove from foods, and may make packaging materials unacceptable. The frass (faecal pellets) combined with the silk and the inevitable sticking together of food particles produces an obvious level of contamination, even though this may be inside the finished packed goods. Cross-infestation by flying moths is possible and can sometimes be caused by infested packaging materials and pallets being brought into food manufacturing areas.
This species causes serious infestations in long-term grain stocks in Germany, although not significantly in the UK. However, a wide range of raw and processed materials is attacked including cocoa beans and manufactured chocolate products.
Control of this species is best achieved by attempting to kill emerging adult moths in the summer months using a residual insecticide applied to likely moth resting places (especially on ceilings and upper walls). If a space spray is to be used it must be targeted to coincide with adult emergence. Moth pheromone traps (which contain a synthetic female sex lure) can help pinpoint emergence dates. However, space sprays on their own (even linked to a monitoring system) are unlikely to be able to kill all emerging adults before some mating and egg laying takes place.
Since the larval stages are rather inaccessible to insecticide treatments (apart from fumigation) subsequent attempts at control should concentrate on the upward migrating larvae seeking a pupation site. Residual treatments of the structure using approved products should be timed to coincide with the migration period of the larvae.
Bulk foodstuffs can only be successfully treated by fumigation in which case a specialist company should be consulted.
Control of the other stored product moths is similar in principle to that described for the warehouse moth. In some species there may be more than one generation per year, particularly at higher temperatures.
Other Moths Associated With Stored Food
Tropical Warehouse Moth (Ephestia cautelIa) – also known as the dried currant moth, and almond moth. Possibly the most commonly occurring storage moth species worldwide and frequently imported into the UK. Very similar to the endemic warehouse moth but larvae often do not diapause and may not survive severe winters in untreated stores and factories. Life cycle, breeding requirements and damage potential are all similar to E. elutella . Larval identification is typically difficult but may be important for determining origin, and for the prevention/control of infestations.
Mill Moth, or Mediterranean Flour Moth (Ephestia kuehniella) . This species has been endemic in Britain for over 80 years. It favours a cereal or cereal product-based diet and is the dominant moth pest in UK flour mills and flour stores and is also a pest in bakeries and shops. Larval silk production is a major cause of blockages of flour chutes and machinery, and can cause product contamination. The distinctly grey forewings and whitish hind wings of the adults may help in identification but larval characteristics are more reliable.
Indian Meal Moth (Plodia interpunctelIa) . The adult moths are easily identifiable (if in good condition) by the distinctive forewing colouration: the third nearest the head/body is a creamy colour and the outer two-thirds are a copper brown (or reddish brown). The larvae may be prominently coloured yellowish or pale greenish, according to the predominant food eaten and they do not have the distinct black speckles of the previous three species. The Indian meal moth is commonly found on imported foods (peanuts, cocoa beans, dried fruit and some cereals) but is less common in the food industry. The larvae diapause and can survive cold winters in buildings and cause serious contamination of raw and processed human foods.
Rice Moth (Corcyra cephalonica) . Adult moths are similar in size to Ephestia spp. but have uniformly coloured pale buff forewings without spots, although wing veins are slightly darker. Larvae are typical, whitish with a brown head. A cosmopolitan pest which is most important in the tropics where it often replaces the mill moth (E kuehniella) as a pest of flour mills. Larvae feed on a wide range of stored products including oilseeds (nuts), cocoa beans, rice, dried fruit, cereals, flour, millet and copra. However it is probably best known as a pest of rice and other cereals, hence the common name. Minimum development temperature is 18 °C. Often
imported from hotter climates, an infestation may continue to develop in the UK but the moth will eventually die out in unheated premises.