Wingspan 13-17 mm.
The smallest of the British Pterophoridae, this delicate little moth is double-brooded, being on the wing in May and June, then again in August.
It is relatively common in the south of England, becoming less so further north into southern Scotland; scarce in Ireland.
The larval foodplant is hemp agrimony (Eupatorium cannabinum), feeding in the stems and forming a gall.
Larva: (description Ian F. Smith)
Foodplant: July and September to April in stem of Eupatorium cannabinum , sometimes causing a slight gall with frass exuding from hole. MBGBI 7-2 indicates two generations in July, and September to April, but 6 mm larvae taken in late July 2004 in Lleyn (I.K. &.I.F.S.) were still larvae in mid August, and 6 mm larvae were found mid August 2004 in St. Helens (Ben Smart).
Length: 6 mm described
Head: Yellow ochre, marked with brown ochre in posterior half. Mouthparts reddish brown. Stemmatal area black.
Prothorax (T1): Large protruding spiracle with black peritreme.
Prothoracic shield coloured as body. Covered in large densely crowded dark brown granules. Divided by medial line devoid of granules.
Thoracic legs: Translucent yellow.
Body: Opaque. Dull yellowish white. Covered in densely packed granules, coloured dark brown on dorsum and in a line extending laterally on the anterior of each abdominal segment. On some specimens, the granules are darker on the posterior body segments, and on A9 and A10 they may merge into a general blackish brown area. Segment A9 formed into a transverse ridge bearing four to six especially large protruding granules on its crest.
Spiracles: Large and prominent with black peritreme. Those on T1 and A9 protruding noticeably.
Pinacula: Insignificant. Seta base pale, surrounded by fine black setal ring.
Setae: Translucent tinted light brown.
Anal plate: Coloured as body or blackish. Covered in densely arranged dark brown or blackish granules. Posterior edge has two especially large protruding granules.
Prolegs: Coloured as body. Reduced, but functional.