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Brown hairstreak butterfly success

Brown hairstreak butterfly eggs by Tom Ward

A scarce butterfly that was almost extinct in the region is continuing to expand its range thanks to conservation efforts.

Volunteers from the West Midlands branch of Butterfly Conservation have been working with land managers, including Worcestershire Wildlife Trust, to help brown hairstreak butterflies move into new areas. The small and elusive butterflies only lay their eggs on young blackthorn; the caterpillars feed on the young buds of the plant when they hatch in spring.

In the 1970s one of the butterfly’s few national populations was confined to Grafton Wood, now jointly owned by the Trust and Butterfly Conservation, in the east of Worcestershire. Since then, volunteers have worked with land managers to manage their hedgerows more sensitively, cutting on a three year rotation in order to allow the eggs to survive winter.

This has allowed the butterfly to expand north to Redditch, south to Pershore and across the border into Warwickshire. It was thought that the M5 was a barrier to further expansion to the west.

Volunteers near a hedge looking for brown hairstreak eggs on young blackthorn growth by Jasmine Walters

Volunteers searching for brown hairstreak eggs by Jasmine Walters

Butterfly Conservation volunteers recently joined volunteers at Worcestershire Wildlife Trust’s Lower Smite Farm, between Worcester and Droitwich Spa, to search for eggs of the butterfly after a single egg was discovered last winter. On the day they found five eggs and Trust volunteers have subsequently found another four, three of which had been laid together, a rare occurrence in itself.

Caroline Corsie, Senior Land Advisor from the Trust, explained “We’ve been watching the incredible success that Butterfly Conservation volunteers have been having in helping this beautiful butterfly to spread into new areas. It’s now found on ten of the Trust’s nature reserves.

“We manage Lower Smite Farm to demonstrate how sensitive farming techniques, such as hedgerow management, can improve the quality of the agricultural landscape for wildlife.

“As well as being important agricultural features – from providing livestock-proofing and shelter for crops - our hedgerows are managed for a variety of wildlife and offer a bounty of food for pollinating insects in spring and summer and berries for birds and small mammals during the winter.

“We’re delighted that brown hairstreak butterflies have found our hedgerows to their liking too. It’s early days but we’re looking forward to seeing more eggs in future years – the adults can be even harder to spot!”

A single egg was found on the farm in 2020 and a further nine have been found so far this year.

According to Simon Primrose, the Brown Hairstreak Champion for Butterfly Conservation in the West Midlands, the eggs were found in four different 1km squares, which suggests that the butterfly is established across the site.

Simon added “This is great news. It’s taken some time for the butterflies to make their way across the M5 so we’re really pleased to have such positive confirmation of their arrival in this part of the county.

“This opens up new potential search areas and more farmers and land managers to work with to assist in the conservation of the butterfly. Of course, more sensitive hedgerow management has the added bonus of helping lots of other wildlife too.

“Just a day or so after finding the eggs at Lower Smite Farm, we found more in nearby hedgerows. We’re looking forward to more searching as the winter progresses and are hoping to see if they’ve had success in moving into Worcester – if anyone would like to join us in the search, please get in touch.”

Brown hairstreak butterfly feeding on hemp agrimony by Pete Walkden

Brown hairstreak butterfly by Pete Walkden

The adult butterflies usually fly high up in the tree canopy and are rarely seen. They congregate around one tree known as an assembly tree, often ash, to feed on aphid honeydew. Whilst adults are sometimes found feeding on common fleabane, bramble and hemp agrimony, the females are often easier to spot as they descend to hedgerows in late August and September to look for suitable places to lay their eggs.

The eggs are usually laid in the fork of a blackthorn that is two to four years old. The adults die off in late autumn and the eggs hatch in spring, with the next generation of adults appearing in late summer.

The Trust’s Natural Networks project, run in partnership with Worcestershire County Council, is also helping land managers to support the spread of brown hairstreak butterflies by providing funding for habitat creation and enhancement.

By working with land managers at a landscape scale, rather than on isolated sites, volunteers have ensured that the butterflies now have a network of hedgerows, trees and shrubs through which to move in order to colonise new areas.