A. iris L. (5()a) is shot with violet-blue in the male, and is distinguished by the white band of the hindwing bearing distally a sharp tooth at the anterior median vein; the outer margin of the forewing is but slightly incurved below the apex.

The nymotypical subspecies is somewhat variable individually, there occurring for instance males with a pure blue gloss (Hungary), instead of violet-blue, or with the white markings flushed with rosy red, the marginal band of the hindwing being cinnamon-brown.

lutescens Schultz, only the female observed, the white bands and spots shaded with darker or paler brownish yellow; likewise rarely met with at large.

— The distribution of the nymotypical subspecies with its aberrations is as follows: Central Europe, Southern England, southwards to Spain, North Italy, Dalmatia, Roumania, Bosnia; Asiatic Russia, Asia Minor (Amasia).

Larva on Salix caprea (sallow), Salix cinerea and aurita; when young brown, slug-like; after the first moult there appear 2 horns on the head, the colour becomes greenish; hibernates young on a pad of silk on a branch of the food-plant near a bud; in the spring (May) the third moult takes place, the body becomes leaf-green with yellow dots and side-stripes on the anterior segments, the head blue-green with red mandibles and white stripes, the horns green, anteriorly blue, edged with yellow laterally, reddish at the lip, forked; two reddish anal processes.

Pupa compressed, bluish green or whitish, head with 2 projections, abdomen with yellowish oblique stripes, duration of pupal stage about 2 weeks.

[3] Females spend most of their lives in the tree canopy, favouring dense and mature oak woodlands, coming down only to lay their eggs on the small willow bushes that grow in clearings and bridleways.

Unlike most butterflies, the purple emperor does not feed from flowers but instead on the honeydew secreted by aphids, sap oozing from oak trees, and on dung, urine, and animal carcasses.

[2][4] Richard South noted that collectors once used animal carcasses "in a somewhat advanced state of decay" to lure the males down to the ground, adding that this practice was "unsportsmanlike"; otherwise one needed a "high net" mounted on a pole about 14 or 15 feet (about 4.5 metres) in length to capture them.

Apatura iris is widely distributed in dense, broadleaved woodlands throughout Europe including southern Britain, and across the Palearctic to central and western China.

In Victorian times this species was regarded as being common in southern England, as far north as the river Humber,[4] but since then it has experienced a sharp decline in both range and numbers.

Heslop estimated from his personal observation that "the minimum number of individual imagines (adults) required to sustain a viable colony in an average year is one thousand";[7] independent confirmation of this has not been found.