Insects of Britain and Ireland: butterflies

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L. Watson and M. J. Dallwitz



Adults. Wingspan 29–38 mm (w-album), or 34–39 mm (pruni); the fringes not banded. Medium built; short-bodied. The eyes white-rimmed; notched or emarginate at the bases of the antennae and contiguous with the bases of the antennal sockets; hairy. Antennae white-ringed, reaching noticeably less than halfway to the wingtips to reaching about halfway to the wingtips; inserted markedly less than one half the width of the head apart. The antennal clubs gradual-elongate (tapered); flattened to not flattened, or not flattened. Labial palps ascending. Having all 6 legs fully developed and operational for walking. Fore-legs without a tibial epiphysis. Tibiae of middle legs 2-spurred. Posterior tibiae 2-spurred.

Forewings. Forewings apically blunt to pointed. The outer and hind margins angled at about 88–100 degrees. The outer margins convexly curved to more or less straight. Uppersides of the forewings dark fuscous, or dark brown; without a discal mark; plain in the males, and in the females of S. w-album; in females of S. pruni with suffused orange subterminal spots towards the tornus.

Hindwings. Hindwings broadly rounded, or trapezoidal; shortly tailed (from vein 2, and in T. w-album this adjoining a short tooth from vein 3); the tail filamentous and delicate to not filamentous; scalloped towards the tornus. Uppersides of the hindwings dark fuscous, or dark brown; conspicuously patterned (in S. w-album), or plain (in S. pruni). Uppersides of the hindwings eye-spotted (or interpretable as such, though rather rectangular, in S. pruni only), or not eye-spotted. The eye-spots 2–4; mid-posterior to near the tornus (in a subterminal row). Uppersides of the hindwings without a discal mark; plain in S. w-album, in S. pruni with orange terminal spots which are more distinct towards the tornus in the female.

Undersides of wings. Undersides of the wings not multiply patterned with pale-ringed black spots or sinuous lines.

Undersides of the forewings brown or ochreous brown, with a white line post-medianly from the costa, this being bent towards the tornus in S. w-album only, and S. pruni exhibiting a faint, interrupted orange band subterminally towards the tornus. Undersides of the forewings not green.

Undersides of the hindwings brown or ochreous brown, with a white line post-medianly from the costa, this sharply double-bent near the tornus only in S. w-album to constitute the characteristic feature of that species, and both species exhibiting a conspicuous subterminal orange band which expands towards the tornus; without a discal mark; with one sharply defined white line. The white line sharply biangulated towards the tornus to form a ‘W’ (S. w-album), or not forming a ‘W’ (S. pruni).

Wing venation. Forewings 10 veined. Forewings with 1 tubular anal vein to with 2 tubular anal veins; the anal veins of the forewings representing 1b only, or comprising 1b and 1c (1c reduced but tubular basally in S. w-album); vein 1b simple. Forewings without a discal cell (the transverse vein weak). Forewing veins cf. L. coridon etc., but the usual short vein 8 lacking in S. w-album.

Hindwings 9 veined; without a praecostal spur; with 2 anal veins; exhibiting vein 1a; the anal veins comprising 1a and 1b. Hindwings with a closed discal cell, or without a closed discal cell; the transverse vein vestigial only, or lacking. The cell-derived hindwing veins 3+4 proximally joined (connate only). Vein 5 absent proximally to the weak transverse vein.

Eggs, larvae, pupae. Eggs discoid, or hemispherical; densely spinulose. The larvae woodlouse-shaped; having no known association with ants (the honey gland reduced or absent). On blackthorn and elm, respectively.

Pupae smooth and rounded, or ridged and angular to smooth and rounded; conspicuously patterned; exposed, with no coccoon; not suspended, but attached at the tail and secured by a median girdle of silk.

British representation. 2 species. Satyrium (Strymonidia) pruni (Black Hair-streak), Satyrium (Strymonidia) w-album (White-letter Hairstreak). The adults abroad June and July, or July.

Status in Britain. Indigenous.

Distribution. Southern Scotland, northern England, English Midlands, East Anglia, Wales, southeast England, central southern England, southwest England, and Isle of Wight. Frequenting woodland and open places. Habitats calcareous and non-calcareous.

Classification. Superfamily Papilionoidea. Lycaenidae.

Illustrations. • Satyrium pruni (Black Hair-streak: B. Ent. 264). • Satyrium pruni (B. Ent. 264, legend+text). • Satyrium pruni (B. Ent. 264, text cont.). • Satyrium w-album (White-letter Hairstreak): photos. • Satyrium pruni (Black Hair-streak) and S. w-album (White-letter Hairstreak): eggs, larvae, pupae. • Larva and pupa of S. pruni: Duponchel (1849). • Larvae and pupa of S. w-album: Duponchel (1849).

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Cite this publication as: ‘Watson, L., and Dallwitz, M.J. 2008 onwards. Insects of Britain and Ireland: butterflies. Version: 16th May 2016.’.