With a wingspan of 24–27 mm, O. latruncula is usually the smallest of the three, although they all overlap in size. Well-marked specimens often have noticeably dark forewings, with a blackish basal area and a coppery brown, rather than whitish, subterminal band. However, melanism is very common in this species and all-dark specimens constitute 100% of the population in some areas.
With a wingspan of 24–27 mm, O. latruncula is usually the smallest among the three species but overlaps in size with them. Well-marked specimens often display prominent dark forewings, featuring a blackish base and a coppery brown subterminal band instead of a whitish one. Melanism is very common in this species, leading to 100% of the population being entirely dark in some regions.