Red Ring Skirt

Adults have a forewing length of 40–53 mm, and females lay on the order of 200 eggs.

Seasonal forms. H. assimilis is seasonally polyphenic. Summer-generation adults have red submarginal spots on the hindwing, while spring-generation adults lack the red spots and are substantially paler, with reduced black scaling — an appearance most pronounced in females. This pale phenotype corresponds to the form long known as nigrivena. Laboratory work on the Kanagawa population showed that the white morph is induced by both short photoperiod and relatively cool temperatures acting together: rearing at 15 °C produced white morphs, whereas 20 °C or 25 °C produced black-veined summer morphs. The temperature-sensitive period fell mainly in the third and fourth larval instars, particularly the fourth, and white morph production was closely associated with markedly delayed larval development. Cool temperature alone was sufficient to produce white morphs even without an intervening larval diapause.

H. assimilis is found from eastern Tibet to most of China, in Hong Kong and in Korea. Its natural range comprises northern Vietnam, southern and eastern continental China, the Korean Peninsula and peripheral islands such as Jeju, together with the Amami Islands of Japan and Taiwan, where separate subspecies occur.

H. assimilis often uses its long proboscis to probe in muddy soil or gravel to get the moisture it needs. The male is strongly territorial, always staying in high positions to defend its territory.