Brown Hairstreak Butterfly - Thecla betulae

Phylum: Arthropoda - Class: Insecta - Order: Lepidoptera - Family: Lycaenidae

The Brown Hairstreak is the largest of the hairstreak butterflies found in Britain. As with other butterflies in this group, it usually holds its wings closed when at rest.

Description

With a wingspan of 38 - 40mm, the males being slightly smaller than the females, Brown Hairstreaks are medium-sized butterflies, but they are scarce and can be very hard to find. Seen in flight from underneath or with wings closed when at rest, they are very beautiful; this comment applies particularly to the females which are even more brightly coloured than the males. The upperwings are brown, and in females they contain large orange splashes on the forewings, while males have much smaller pale forewing spots.

Distribution

Very much a southern species in Britain, this butterfly is rare and localised in southern England and in west Wales, while in Ireland its main strongholds are in the Burren, County Clare, and in the south-east of County Galway. This species is also found in many parts of mainland Europe and Asia.

Lifecycle

Spending much of the time in the tops of tall Ash trees, Fraxinus excelsior - now, of course, being felled in great numbers due to Ash Dieback Disease - adult Brown Hairstreaks are also seen along woodland edges and dense hedgerows, particularly those containing Blackthorn Prunus spinosa. The adults also take nectar from various kinds of wildflowers including Brambles Rubus fructicosus, Common Ragwort Senecio jacobaea, and Hemp Agrimony Eupatorium cannabinum.

The main larval foodplant of the Brown Hairstreak is Blackthorn. The amazingly intricate eggs are laid in late August and hatch the following April.

The green, slightly hairy caterpillars are plump and have rows of short diagonal whitish dashes along the sides. They feed at night, resting on the undersides of blackthorn leaves during the daytime.

When fully grown the larvae pupate among the dead twigs and leaf litter beneath Blackthorn bushes. The adult butterflies emerge from early August.

Acknowledgements

This page includes pictures kindly contributed by Betty and Tony Rackham and by the Countryside Council for Wales.

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