Insects of Britain and Ireland: butterflies
Adults. Wingspan 90–120 mm; the fringes conspicuously light-and-dark banded. Slender-bodied to medium built; very short-bodied. The eyes glabrous. Antennae reaching noticeably less than halfway to the wingtips. The antennal clubs gradual-elongate; curved; not flattened (blunt, very briefly pale-tipped). Labial palps ascending. Having only 4 fully developed legs. Fore-legs without a tibial epiphysis (with the fore tarsus of the female differing from that of the male in ending in a spiny knob). Tibiae of middle legs 2-spurred. Posterior tibiae 2-spurred.
Forewings. Forewings apically blunt. The outer and hind margins angled at about 110 degrees. The outer margins concavely curved. Uppersides of the forewings orange-brown; contrastingly dark-veined; without a discal mark; blackish over the veins and enclosed by a blackish marginal band, the latter extending along the dorsum and enclosing yellowish and red-orange spots towards the apex and around the outer margin, and white spots apically and towards the middle of the costa.
Hindwings. Hindwings broadly rounded; with the outer margins not scalloped. Uppersides of the hindwings orange-brown; conspicuously dark-veined; conspicuously patterned; without a discal mark; coloured like the forewings, with black veins and marginal band, males with a black glandular spot on vein 2 before its middle.
Undersides of wings. Undersides of the forewings colour-patterned like the uppersides, but paler and the white spots larger; conspicuously dark-veined.
Undersides of the hindwings patterned like the uppersides, but honey-coloured instead of orange-brown, and greenish proximally at the costa; conspicuously dark-veined.
Wing venation. Forewings 12 veined; without basally dilated veins. Forewings with 1 tubular anal vein; the anal veins of the forewings representing 1b only; vein 1b simple. Forewings with a discal cell; vein 2 departing from the cell less than three-quarters of the distance from its base (from about halfway). Forewing veins 8 and 9 out of 7, 10 connate with or from near the base of 7, 11 from the distal front of the cell, 12 free.
Hindwings 9 veined; with a praecostal spur; with 2 anal veins; exhibiting vein 1a; the anal veins comprising 1a and 1b. Hindwings with a closed discal cell; the transverse vein complete. 7 veins arising from the hindwing cell. The cell-derived hindwing veins all arising independently of one another.
Eggs, larvae, pupae. Eggs very shortly truncate-fusiform (much broader at base than apex); longitudinally ribbed (with about 20 longitudinal ribs, and numerous fine cross-linking ribs). The larvae hairless; with a pair of tentacles from segment 2 (and another, shorter pair on segment 12; non-retractile); without bristly spines; exposed feeders. On Asclepiadaceae and Apocynaceae.
Pupae smooth and rounded; conspicuously patterned; with shining-metallic markings; exposed, with no coccoon; suspended from the tail (cremaster), with no median silk girdle.
British representation. 1 species. Danaus plexippus (Milkweed, Monarch), adventive. The adults abroad July to September.
Status in Britain. Adventive. The capture of occasional specimens of the Milkweed in Britain since 1876 more or less corresponded with the introduction of regular transatlantic steam shipping services.
Distribution. Southeast England, central southern England, southwest England, and Ireland. Frequenting open places. Habitats calcareous and non-calcareous.
Comments. A famous migratory butterfly, the flight powerful, sustained and often gliding. Distasteful to predators.
Classification. Superfamily Papilionoidea. Danaidae.
Illustrations. • Danaus plexippus (Milkweed, Monarch): photos. • Danaus plexippus (Milkweed, Monarch): egg, larva, pupa. • Danaus plexippus (Milkweed, Monarch: Morris, 1893).
To view the illustrations with detailed captions, go to the interactive key. This also offers full and partial descriptions, diagnostic descriptions, differences and similarities between taxa, lists of taxa exhibiting or lacking specified attributes, and distributions of character states within any set of taxa.
Cite this publication as: ‘Watson, L., and Dallwitz, M.J. 2008 onwards. Insects of Britain and Ireland: butterflies. Version: 16th May 2016. delta-intkey.com’.