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Brown Hairstreak

Thecla betulae

  • Family: Gossamer-winged butterflies – Lycaenidae
  • Subfamily: Hairstreaks – Theclinae
  • Wing span: Small–medium-sized, 25–40 mm (0.98–1.56 in.). Largest of the Hairstreaks. Females usually larger than males.
  • Wing upper side: Brown, trailing edge of hind wing and spur orange. Females’ forewing with orange lateral strip.
  • Wing underside: Different shades of orange. Hind wing and forewing with darker, white-edged stripe. Margins brighter orange.
  • Habitat: Grazing land with trees and bushes.
  • Flying time: August.
  • Overwintering form: Egg (containing developed caterpillar).
  • Larval foodplant: Blackhorn (Prunus spinosa) and bird cherry (P. padus).

The brown hairstreak is rare, only found in southern Finland, and is quite a late flyer. It can be differentiated from its close relatives by the orange colour of the underside of its wings and its white-edged lateral strip. Like all the hairstreaks (except the green hairstreak), the brown hairstreak also has a small spur on its hind wing. (As does the short-tailed blue, which is a member of the Blue family). The upper side of the brown hairstreak’s wing is difficult to study because it keeps them pressed together when it is at rest.

Males defend their territory in the crowns of trees or on hill-tops as they wait for females, who lay their eggs individually or in pairs on new branches in the host plant.

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