Mimathyma nycteis is a butterfly found in the East Palearctic (Amurland, Korea, Northeast China) that belongs to the browns family.

fulva], differing very considerably from the same, resembling certain species of the genus Athyma on the upperside, especially in the cell of the forewing bearing a white longitudinal streak along the median vein.

Female similar to male larger, rarely with a row of red-brown spots near the outer margin of the hindwing.

Larva slug-like, dark green, laterally with light oblique stripes, segments 6—12 each with 2 thorny processes, those on segments 6, 8 and 11 being longer and thicker than the others, at the apex of the body 2 long, pointed processes; on the head 2 long thorny horns, which terminate each in 2 roundish knobs directed forward; head and back with single small short thorns, which are longest on the sides of the head, where they also stand more closely together; the parts of the body ventrally of the spiracles clothed with minute yellowish hairs; ventral surface paler than the back; length of the adult larva 52 mm.

Pupa whitish green like that of ilia and iris, but bearing a row of obtuse tubercles on the sharply keeled dorsal side of the abdomen (according to Graeser).