Stygian ringlet

It has a wingspan of 46–56 mm.[2] The upperwings of both sexes are mostly brown with reddish bands near the edge (postdiscal bands). The bands vary in size and may be dusted with brown in the males.[3] Within the bands are a variable number of eyespots (ocelli); these are black with white centres. The forewing has a large eyespot near the tip, often with two white centres. The hindwing has three or four spots.[3]

The underside of the male's forewing is largely orange with brown dusting in the basal half and a brown border. Unlike in the Styrian ringlet, the brown border does not taper towards the rear of the wing and has a dark "tooth" projecting into the orange[3][4] The tooth is less conspicuous in the females. The underside of the hindwing is mostly brownish, darker in the basal half.[3]

The subspecies E. s. triglites of the Bergamo Alps and Monte Generoso is more strongly marked than the nominate subspecies E. s. styx. It has a larger postdiscal band and larger eyespots on the upper forewing while the underside of the hindwing sometimes lacks eyespots.[4]

The subspecies E. s. trentae of the Julian Alps is even more strongly marked. It has large eyespots with bright white centres.[4]

It occurs in the Alps at altitudes of 600–2,200 metres. It is found in northern Italy from near Monte Generoso to the Dolomites, in Ticino canton in south-east Switzerland, in the Allgäu Alps in south-east Germany, in parts of Austria and in the Julian Alps in Slovenia. It inhabits steep limestone slopes with scattered trees and bushes. It favours warm, dry, rocky areas.[4]

The barrel-shaped eggs are grey-brown with brown spots and prominent ribs.[3] The caterpillars are grey-brown with lighter and darker stripes and can reach 20–25 mm in length.[3] They feed on grasses, particularly Sesleria varia. They take up to two years to mature, hibernating during the first and penultimate instars.[3] The butterfly pupates among stones and grass in a green and brown chrysalis.[3] The adults fly from early July until early September. A single brood is produced each year.[4]

Named in the Classical tradition.Styx was the name of an Oceanid nymph, one of the three thousand daughters of the Titans Oceanus and his sister-wife Tethys, and the goddess of the River Styx. Others make her one of the progenies of the primordial gods, Nyx (Night) and Erebus (Darkness)