THE BROWN HAIR-STREAK. (Thecla Betulæ.)
([Plate XII]. fig. 1, Male; 1 a, Female.)
The genus to which this butterfly belongs, contains five British species, elegant and interesting insects, though not gaily tinted. They are most obviously distinguished from other small butterflies by the tail-like projection on the lower edge of their hind wings (though one of their
number, T. Rubi, has this very slightly developed). From each other they are best distinguished by the characters on their under surface, where they all bear a more or less distinct hair-like streak, whence their common name—Hair-streak.
The Brown Hair-streak is the largest of the genus, measuring sometimes an inch and two-thirds in expanse. The two sexes differ considerably on the upper surface, the male being of a deep brown colour, slightly paler near the middle of the front wing, while the female possesses on the front wing a large patch of clear orange. Both sexes have several orange marks upon the lower angles of the hind wings. Beneath, the general colour is tawny orange with duller bands, and marked with one white line on the front wing, and two parallel white lines on the hind wings.
The caterpillar is green, marked obliquely with white; it feeds on the birch and also on the sloe.
The butterfly appears in August, continuing into September. It is generally distributed through the south, but is by no means an abundant insect. Mr. Stainton observes that it has a habit of "flitting along in hedges just in advance of the collector;" but it is also found in oak woods in company with the Purple Hair-streak.
Forty were taken in a season in woods near Henfield, Sussex. Other localities are, Underbarrow Moss, Westmoreland; North Lancashire, common in some parts; Preston; Valley of the Dovey, Montgomeryshire;
Cardiff, S. W.; Barnwell Wold; Peterborough; Colchester; Epping; Darenth Wood; Coombe Wood; Brighton; Tenterden; Winchester; Woolmer Forest, Hants; Plymouth; Dartmoor; Wallingford, Berks; Ipswich; Dorsetshire; Norfolk; Wiltshire; Monks Wood, Cambridgeshire.