Wingspan 10-12 mm
Caloptilia semifascia flies from late July to October and again, after hibernating, until May. It is widespread in southern England and South Wales, but usually restricted to localities where Field maple, Acer campestre, is common. Outlying populations occur in Caernarvonshire-Denbighshire and in Cumbria-Yorkshire.
The angled light streak starting at the leading edge of the forewing is characteristic, but it can be obscured on darker specimens.
The larva feeds on field maple in June and July and, occasionally, in late August and September. At first it inhabits a leaf mine, then a leaf cone and, finally, a sequence of two leaf rolls.
Occasionally, sycamore, (Acer pseudoplatanus), in the vicinity of heavily infected field maple is eaten. The feeding signs can be confused with those of C. rufipennella on sycamore, so records of C. semifascia from this tree species should only be made if the adult is reared to confirm the identification.