Since it was first discovered in Britain in west Dorset in 2001, Cosmopterix pulchrimella has spread rapidly. Initially the main spread was along the south coast but it is now found inland and as far north as Cambridgeshire.
The larvae mine the leaves of Pellitory-of-the-Wall Parietaria judaica, forming an irregular blotch. The mine initially looks whitish but rapidly turns brown. If held up to the light, a fine speckling can be seen within the mine. The mine shown below is occupied but the larva is often surprisingly difficult to see, in this instance it is at the far left hand end of the mine.
No other Lepidoptera are known to mine Pellitory in Britain but three Agromyzid flies have been recorded. These all make gallery mines. Sometimes the gallery mines can be sufficiently contorted that they form a false blotch but the gallery nature of the mine can still be determined and there are distinct frass grains so confusion with C, pulchrimella should not occur.
Large quantities of the foodplant are not needed, even a small isolated plant can be occupied. The attractive moth can easily be bred.