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Record numbers of eggs of the rare brown hairstreak butterfly have been found in south-west Wales after landowners stopped flailing hedges every year.
The butterfly lays its eggs on blackthorn every summer. But when land managers and farmers mechanically cut hedges every autumn, thousands of the eggs are unknowingly destroyed.
Conservationists have now persuaded landowners to cut hedges in a more gentle rotation, with sections left uncut for up to three years, to enable more eggs to survive over winter. The caterpillars emerge with the foliage in spring and hatch into adult butterflies in July.
The brown hairstreak is difficult to spot as a butterfly but every winter volunteers assess its populations by counting its minuscule cream-coloured eggs, which with careful searching are visible on the bare branches of blackthorn.
Volunteers for Butterfly Conservation this winter counted 276 brown hairstreak eggs on blackthorn hedges on the north verge of the busy A40 west of Llandeilo and 117 eggs on the south verge – both record counts and a 50% increase on the previous year. Three nearby sections of hedgerow also recorded increases after sympathetic management, including the planting of new blackthorn bushes.
The upturn comes after more than a decade of decline for the butterfly in the Tywi valley, which almost disappeared in the region due to increased mechanical flailing of hedgerows and patches of scrub.
When Butterfly Conservation found a small remnant population in 2021 west of Llandeilo, they began annual egg counts and worked with the National Trust and the South Wales Trunk Road Agent, to get more blackthorn planted, as well as protecting hedgerows from annual flailing.
A nearby group of fields that were not managed in the same way, and had their hedgerows flailed recorded a drop from an average of 60 eggs each winter to four this year.
“The West Wales volunteer team of BC’s South Wales branch are really excited to find that, after a decade of heartache for brown hairstreak butterflies in Carmarthenshire’s Tywi valley, there is at last signs of an upturn,” said Richard Smith, who has overseen the conservation efforts as a volunteer for Butterfly Conservation.
“Fortunately, the Welsh government’s brand new sustainable farming scheme (SFS) requires avoidance of annual flailing. We plan to work with them and local hedge-layers to maintain this trend and save the species in the valley.”
Dan Hoare, the director of nature recovery for Butterfly Conservation, said: “Across the UK, hedgerows are an essential part of our ecological infrastructure, providing homes and highways to millions of insects, mammals and birds – but since the 1950s we have lost about 40% of what we had, and less than half of what remains is thought to be in a good condition.
“We don’t want to stop anyone managing their hedgerows, but we would love more landowners to try cutting back on their cutting back: if hedgerows are only trimmed once every two years, or even every three years, it could make an enormous difference to the survival of the brown hairstreak and help many other species as well. The lovely brown hairstreak is an indicator of getting that balance right.”
