It is an established fact that many insects which are now serious pests were once harmless species living on wild plants and other ”natural” sources of food. As soon as mankind provided their natural food, or at least an adequate substitute for their natural food, in bulk by cultivating plants, these animals were able to multiply to such an extent that they became a very serious problem. A well-known example is the Colorado Beetle (Leptinotarsa decemlineata) which originally lived in North America on a few wild species of Solanaceæ, but later attacked the introduced potato plants and thus became the worst insect pest of potato crops, not only in its native country, but also in Europe. Clothes Moths and Carpet Beetles are also serious pests because they are highly specialised in their nutritional requirements and use the protein keratin as a staple food. Keratin also happens to be the main constituent of wool and hair, the essential fibres for our winter clothing, our blankets, carpets, rugs, upholstered furniture and other textile materials, fur goods, etc. It goes without saying that these articles only became available at the time when prehistoric man started to use animal skins as clothing and to live in more or less permanent settlements. It is most unlikely that the evolution of the Clothes Moths and Carpet Beetles coincided with the early history of human civilisation. Consequently only the alternative remains, viz., that these insects were already living on accumulations of keratinaceous material available in nature and only became pests because man, most conveniently from the point of view of the insects, assembled considerable quantities of wool and hair.