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 typically the smallest among the three species, though they all share similar sizes. Well-marked specimens frequently exhibit prominent dark forewings with a blackish base and a coppery brown subterminal band rather than a whitish one. However, melanism is very common in this species, and 100% of the population can be entirely dark in some areas.