(Left) Northern Winter Moth (O.fagata)
(Right) Winter Moth (O.brumata)
When seen side by side, the size difference between the two species
is obvious. The two species show no overlap in wingspan, 32-40mm for
fagata and 22-28mm for brumata. O.fagata has pale,
off-white hindwings, whereas O.brumata is generally a darker,
browner and stronger-marked species, although as the individual illustrated
here demonstrates, coloration does vary.