Apatura iris

Apatura iris, the purple emperor, is a Palearctic butterfly of the family Nymphalidae.

Description
Adults have dark brown wings with white bands and spots, and a small orange ring on each of the hindwings. Males have a wingspan of 70 –, and have a purple-blue sheen caused by iridescence that the slightly larger (80–92 mm) females lack. The larvae (caterpillars) are green with white and yellow markings, and have two large "horns" at the anterior end and a smaller one at the posterior.

Description in Seitz
A. iris L. (5a) 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. Female larger than the male, somewhat more broad-winged, brown, without blue gloss. 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. Of known aberrations the following have received names: ab. thaumantis Schultz, the white markings enlarged and widened, the elsewhere but feebly marked pale spots larger and sharper, especially at the margin of the hindwing, on the underside of the forewing the russet-red scaling restricted by the widening of the black markings; in the hindwing the narrow dark marginal line is wanting, the white median band is more or less shaded with black; so far only males have been found at large, and but  rarely, also artificially produced by experiments with temperature. — ab. jole Schiff. (50b, transition), the counter-part of the preceding: the white markings obsolescent except the subapical spots of the forewing, the latter also sometimes absent, the whole black wing-surface shot with blue. In all transitions towards the main form, also asymmetric specimens occur; occasionally with pale radiating smears in the distal area of the hind- wing. Everywhere rare among the main form, both sexes being known. — ab. lutescens Schultz, only the female observed, the white bands and spots shaded with darker or paler brownish yellow; likewise rarely met with at large. — Very singly there occur in this species females in which the upperside is irrorated with golden scales, which are more condensed in the posterior area of the forewing and the anterior area of the hindwing; this is ab. aurosquamosa Gillm. — 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). — Egg cylindrical, ribbed, yellowish or greenish, somewhat tinged with red. 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. Pupation the end of May or in June. Pupa compressed, bluish green or whitish, head with 2 projections, abdomen with yellowish oblique stripes, duration of pupal stage about 2 weeks. The butterfly at the edge of and in leaved woods, in the early morning found drinking on dewy roads in the woods and at puddles; it  becomes more restless at a later hour, flying at a considerable height, is fond of foul-smelling matter (excrements, dung, urine, cheese) and is easily baited with them. The flight is strong and graceful. The butterfly rests with spread wings on a leaf of a tree or shrub and has, like the preceding species, the habit of returning to its resting-place or near it, if disturbed. The females rarely come down to the ground, remaining generally in the tree-tops. — In Amurland the brownish colour of the bands and spots is the rule in the female (cf. lutescens); the male is of especially large size, the ground-colour of the wings being less dark and the gloss stronger and of a lighter  reddish blue. We have here do with a local form, for which it appears expedient to introduce the name amurensis subsp. nov. — In bieti Oberth. the markings are brownish yellow in the male, and resemble in shape and position those of the European form; but the blackish spot in the anal area of the forewing is eye-like, having a blue pupil, the eye-spot of the hindwing is enlarged and this wing bears, besides median band two other brownish transverse bands situated in the distal area. In the female the markings are yellowish, except the white subapical spots of the forewing. Tibet, West and Central China, in June and July, up to about 3000 m. — Along with this brown main-form there flies in the same districts a form which is white-spotted in both sexes, but is much larger than the European race and has a deeper chocolate-brown underside; it approaches the Amur form and may be named recidiva form. nov. in the female of this form there is usually still a dull, ochreous marginal band visible on the hindwing.

Habits
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. Males also spend much of their time in the tree tops, defending their territory from rivals, though they will sometimes descend to drink from puddles or feed. 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.

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. Heslop et al. noted that the males' penchant for roadkill can often cause them to be killed by cars.

Life cycle
They lay eggs in late summer on the upperside of sallow leaves, preferring the broad-leaved sallow, Salix caprea, but they will also use the narrow-leaved sallow, Salix atrocinerea, and various species of poplar. (Poplar is a more common food plant in continental Europe than in the British Isles. ) After hatching, the larvae will lie along the midrib of the leaf where they are well camouflaged, and feed only at night. During the winter they hibernate in the forks of sallow branches, where they change colour from green to brown to match their surroundings. (The larvae are variously stated to be reach 35–40 mm long when fully fed or 55–56 mm; it is hard to give definitive measurements, given that they lack a rigid structure.) The following June they form a pale green chrysalis, 30–35 mm long and 12–15 mm in width, resembling a leaf shoot. The adults usually emerge in July, flying well into August.

Distribution
Apatura iris is widely distributed in dense, broadleaved woodlands throughout Europe including southern Britain, and across the Palearctic to central and western China. Different subspecies are found across the region (see below).

British Isles
In Victorian times this species was regarded as being common in southern England, as far north as the river Humber, but since then it has experienced a sharp decline in both range and numbers. This decline started in the first part of the twentieth century (it was noted by South, for example, writing in 1921) and by the 1960s it was relatively scarce, being confined to old broadleaved woodlands in a few counties in south-east England. Heslop et al. ascribed the decline to habitat fragmentation and loss, starting before the First World War but accelerated by the increased demand for timber during that war, causing old woodlands to be clear felled to make way for commercial forestry crops, especially softwoods. This rendered large parts of its former habitat unsuitable, and it died out in those areas. This process continued after the Second World War for the same reason. 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"; independent confirmation of this has not been found.

South believed that once they had become uncommon, increased collecting had contributed "to the monarch's destruction" in many areas. By 1989 the species had a stronghold in the remaining large broadleaved woodlands of Hampshire, Surrey and Sussex, but was still found in scattered localities elsewhere across southern England. It has returned in large numbers to the Knepp estate in Sussex following re-wilding, as described by Isabella Tree.

South noted that it had not been recorded from Scotland, and only doubtfully from Ireland, adding that "in Wales it is only found in Monmouthshire."

Subspecies

 * Apatura iris iris
 * Apatura iris bieti Oberthür, 1885 (Tibet, western and central China)
 * Apatura iris xanthina Oberthür, 1909
 * Apatura iris kansuensis O. Bang-Haas, 1933
 * Apatura iris amurensis Stichel, [1909] (Amur, Ussuri)

Cultural reference
A specimen of Apatura iris plays a key role in solving a murder mystery in Robert W. Chambers' 1897 short story, "The Purple Emperor." The species is also mentioned in Tolkien's The Hobbit, in chapter 8, "Flies and Spiders".