Wingspan 11-14.5 mm.
The adult moth has yellowish ochre veins, but the species is more easily identified at the larval stage by its distinctive case made of rings of mined leaf, fully developed in May. The preferred food plants are black horehound (Ballota nigra) and hedge woundwort (Stachys sylvatica), but it is occasionally found on other Labiates. The mines are large and obvious on the upper side of the leaf, betraying the larva or larvae on the lower side.
The adult flight period is from late June to August, sometimes coming to light. Cased larvae occur from September to May, but are small until March, after the winter diapause.
The species is common, where the preferred foodplants occur, in southern England and Wales, but it becomes scarce and local in Cheshire and from south Yorkshire to the northern limit of England.