Caloptilia semifascia is a small moth with a wingspan of 10 to 12 mm. The angled light streak starting at the leading edge of the forewing is characteristic, but it can be obscured on darker specimens. The larva mines the leaves of Sycamore. The early mine is a gallery leading to a squarish blotch. It later forms up to three successive tubes or cones by folding the tips of leaves downwards . The moth must be bred to identify.

Adult Leafmine must be reared to adult

Larval stage: The mines/leaf-folds cannt be distinguihed from other Caloptilia on Acer; the larva must be reared so that the adult can be identified.  

Wherever Acer species are present, notably Field Maple, Sycamore or Norway Maple.

Flies from late July to October and again, after hibernating, until May.

Has been recorded on various Acer spp., including Field Maple, Sycamore and Norway Maple.

It is widespread in southern England and South Wales, but Outlying populations occur in Caernarvonshire-Denbighshire and in Cumbria-Yorkshire. In the Butterfly Conservation's Microlepidoptera Report 2011 this species was classified as local.

Occasional in Leicestershire and Rutland.

Caloptilia sp. cones on Acer spp. are no longer considered to be reliably identifiable without rearing to adult for det. This follows the colonisation of Caloptilia honoratella and the re-colonisation of Caloptilia hemidactylella, a re-appraisal of foodplant preferences, plus potential for colonisation by other European Acer-feeding Caloptilia spp.

Plant C, (2022), The Status of Caloptilia honoratella (Rebel, 1914) and Caloptilia hemidactylella ([Denis & Schiffermüller], 1774) in Britain with a note on two similar additional Acer-feeding Caloptilia that might appear in Britain (Lep,; Gracillariidae). Entomologist's Rec. J. Var. 134;1, 21-39