Wingspan 7-9 mm.
A variable species, some specimens appearing very dark and some much paler. There is a broad whitish basal streak which is usually quite obvious.
The larvae feed on alder (Alnus spp.) including Italian alder (A. cordata), creating a small triangular blotch mine on the underside of the leaves.
It is quite a common species throughout the British Isles and the adults fly in two generations; in May and again in August.