Blog written by Robin Griffiths, December 2021

Visitors to Wiltshire Wildlife Trust reserves in Braydon Forest may notice pieces of red wool tied to some Blackthorn plants. These are to indicate there are Brown Hairstreak eggs on the plants, and are there in order to alert workers to the existence of the eggs and to prevent them cutting those plants.

The eggs are laid in late summer and hatch in spring, so the larvae can eat fresh young leaves and then pupate on the ground and emerge as adults in August.

Why do we search for Brown Hairstreak eggs? Most other species of butterfly and moth are most easily seen as adults – not so the Brown Hairstreak! Adults are extremely elusive and hard to see – they don’t nectar on flowers to any great extent and spend their time either feeding on honeydew high in Ash Trees or in the case of the female, searching for suitable Blackthorn for egg laying.

The eggs – round and white – show up well against the dark wood of the Blackthorn stems so in fact a better idea of the species’ status and range is had from doing the egg searches in winter than in looking for the butterflies, despite the fact that the female in particular is one of the most beautiful butterflies in the UK.