Male upperside is smoky black, with some silvery blue scales. Female upperside is a dark brown, without traces of blue. This butterfly's small size, colouring and tendency to fly close to the ground make it easy to overlook.
Wingspan 18 - 27 mm.
In the north, there is only one brood. Adults emerge in late May, and can sometimes be seen on the wing into early July. Ova are laid in June in the flower heads of kidney vetch, and hatch after 6 - 21 days. The larval period lasts about 9 months, spanning the winter months and emerging again from mid-April. The pupal stage lasts up to 18 days.
May to July.
Most of the colonies in this area are located around the Moray Firth Coast. However, it also occurs in isolated colonies on the north coast of Caithness.