Blue butterfly once extinct in UK now thriving

“It demonstrates that we can reverse the decline of globally-threatened species,” say researchers

The blue butterfly now has a population of around 750,000 in Britain (Jeremy Thomas)

A butterfly once thought to have gone extinct is now thriving in Britain after 150 years.

Thousands of the large blue butterfly have been recorded in south-west England, thanks to a conservation project by the Royal Entomological Society.

“This success shows that if we can understand the ecological requirements of very rare and difficult species, we can turn back the trend of decline,” said ecologist David Simcox.

The large blue butterfly was declared extinct in the UK in 1979, and attempts to reintroduce the species began four years later as researchers brought caterpillars over from Sweden.

Mr Simcox, who was involved in reintroducing the butterfly alongside Oxford University professor Jeremy Thomas, said it was “incredibly satisfying” to see the species thriving again.

“I didn’t have a grey hair on my head when I started. Now it’s all grey,” he told BBC News.

He said while he and his colleagues were hopeful for the species return, they did not expect such a successful comeback.

Britain is now home to the largest known population of blue butterflies (Royal Entomological Society)

“Obviously you have hope, but the first 10 years were difficult, the national population was under 10,000 eggs,” Mr Simcox added.

This summer, conservationists recorded around 750,000 blue butterfly eggs across 40 sites.

They estimate that some 20,000 of those butterflies flew, making south-west England home to the greatest number of blue butterflies in the world, according to the Royal Entomological Society.

But researchers warn that the species remains endangered and extreme weather and climate change could impact their survival.

Mr Simcox said: “The greatest challenge ahead is to secure this expansion in a warming climate and to develop strategies to mitigate the impacts of extreme weather events.”

Many other rare insects, including eight other species of butterfly, the Shrill carder bee and the Rock-rose pot beetle among others, are also now thriving after conservation work across Somerset and in the Cotswolds.

Prof Jeremy Thomas said: “The unprecedented success of this project is testimony to what large scale collaboration between conservationists, scientists and volunteers can achieve.

“Its greatest legacy is that it demonstrates that we can reverse the decline of globally-threatened species once we understand the driving factors.”