Lepidoptera The Brown Hairstreak Butterfly – Thecla Betula
The five Hairstreaks which constitute the genus Thecla are all pretty insects, characterised by hair-like streaks on the under surface.
Betula is the largest of these. Its upper surface is of a deep brown colour, with orange-brown marks at the anal angles of the hind wings, and, in the female, a large patch of orange on the fore wings. The under side (Plate VI, fig. 3) is orange brown, much lighter in the male than in the female. On the fore wings are two white lines, the inner one of which is indistinct; and on the hind wings are two others, the outer one being longer and more distinct than the inner.
This butterfly is by no means an abundant insect, though it is widely distributed, and in some places plentiful. Its chief haunts are woods, and we may mention among its favoured localities Epping Forest, Monk’s Wood in Cambridgeshire, the wooded parts of South Devon and Dorset, New Forest, Colchester, and Peterborough.
The perfect insect is on the wing from July to October, and the eggs are deposited in the autumn on the twigs of its food plant-the blackthorn (Prunus spinosa). These do not hatch till the following spring. Toward the end of June the caterpillar is fully fed.
The colour of the caterpillar is light green, with two white stripes down the back, and two others along the sides. There are also two small oblique whitish lines on each side of each segment.
The chrysalis is smooth, and of a pale brown colour.