Between June and July, and then again in September, the leafmines of the gorgeous little moth Mompha raschkiella (check out the adult on the UK Moths website here) can be found on their food plant Rosebay willowherb (Chamaenerion angustifolium).

Beginning with a narrow linear mine that frequently follows the leaf’s midrib, the larvae chew their way along the leaf, eventually creating a blotch with a slight yellow caste that’s scattered with its poop (frass). When fully grown, the larvae cut a slit in the leaf, dropping to the ground to pupate. You can read further and see more images on the British Leafminers website.