Butterflies are easily recognised from other types of insects by their four large wings that are studded with coloured dust that rubs off easily. Mouth parts are built like a proboscis, which when not in use is rolled up like a spring under the head. Butterflies have complete metamorphosis and development from egg to adult progressing through a series of larval stages and a pupal stage. Butterfly larvae are elongated, with a well developed head capsule and biting mouth parts. They have three pairs of short, jointed legs on the thorax joints and on the abdomen there are five pairs of prolegs with small crochets.

We know about 40 different butterfly species, which occasionally can cause damage to food. Most of them are quite rare, but when they occur they can do significant damage. Both butterflies and moths are members of the order Lepidoptera. When it is bright, adult moths are very passive. In twilight they fly around to find a mate or to find a suitable place to lay eggs. The adult moths do not exactly damage goods. A few hours after the adult moth has come out of the cocoon and has mated, the egg laying begins. The eggs are generally laid directly in products. If the product is packed in such a way that the smell escapes through small cracks, it will be at these cracks eggs are laid. The small newly hatched larvae would then be able to find their way in through the cracks. Goods in dense, undamaged packaging are protected against moth infestations.

Newly hatched larvae immediately begin to spin and eat. Webs in goods show with certainty that it is moth larvae that have been at stake. The web, a kind of silk, comes from the lower lip of larvae. It is sticky and whatever the larvae live in along with its droppings gets stuck in these threads. As the adult moths, larvae also shun the light, but when they grow up they climb to the surface of whatever they have lived in. At this point they can easily chew their way through paper and plastic, which block the way. They pupate either on the surface of a product or go hiking, often towards walls, to find a crack or crevice where they can comfortably pupate. Pupation often begins with the larva spinning a dense shell around itself.

Moth larvae are quite greedy and not very picky. Virtually all types of cereals, flour and other cereal products, bakery products, dried fruit, nuts, chocolate and marzipan can be eaten by moths; but it will usually be the case that the individual species specialise in certain goods. Goods with fibre threads are unsuitable. Aside from that, there is no actual hygienic problems associated with moths and moth larvae, but the goods are disgusting and even a single larva in a piece of chocolate can trigger strong reactions from consumers. Goods containing moths are not usually welcome. As moths and especially moth larvae can be very difficult to determine, even for entomologists and as many quarantine rules undoubtedly intended to prevent the import of moths in general, you have to know that goods containing moth larvae – of whatever nature – will be treated as quarantine goods in the importing countries which have moths on quarantine lists.