Large blue butterflies return to Rodborough Common on the Cotswolds for the first time in 150 years

The large blue has been successfully reintroduced to Rodborough Common. Credit: David Silcox

The largest reintroduction of a rare butterfly that was once extinct in Britain is a success after the insects bred in the first year at a site on the Cotswolds.

The globally-endangered large blue butterfly was introduced to Rodborough Common in Gloucestershire in August 2019.

It is the largest and rarest of all nine British blue butterflies and was declared extinct in Britain in 1979.

It was re-introduced to a number of sites in England from the continent but the scheme at Minchinhampton and Rodborough Commons is the largest of its kind. Around 1,100 caterpillars or larvae were released on the 867-acre site owned by the National Trust.

The large blue larvae trick a species of red ant into carrying them into their nest and caring for them while they feed on ant grubs. Credit: Sarah Meredith

Large blue butterflies have a remarkable life cycle, which involves the larvae tricking a particular species of red ant into carrying them into their nest, where they feed on ant grubs before emerging the next year as butterflies.

The project works because it has been able to create the right conditions for the ant. It also encouraged the growth of wild thyme and marjoram, which the butterfly feeds and lays its eggs on.

The Commons cows keep the grass down so sunlight can reach the soil, warming it to create perfect conditions for the red ants. Credit: David Silcox

A number of organisations came together to do the preparation work, controlling scrub and creating grazing areas for the Commons cows to provide ideal conditions for those crucial red ants.

Those who helped were:

  • National Trust

  • Butterfly Conservation

  • Limestone's Living Legacies Back from the Brink project

  • Natural England

  • Royal Entomological Society (RES)

  • Minchinhampton and Rodborough Committees of Commoners

Now an estimated 750 butterflies have successfully emerged at the site over summer 2020.

The large blues have been recorded mating and laying eggs and have also been spotted away from the release site.

A sign of the project's success - a pair of large blue butterflies mating on Rodborough Common. Credit: Sarah Meredith

Richard Evans, Area Ranger for the Commons says, “Large blues were once a common sight on the commons but some of the grassy slopes had become overgrown which had a severe impact on the red ant’s habitat.

"The long grass and scrub had caused the soil to cool which made it difficult for the ants to survive. As the ant population dwindled in the late nineteenth century, so did the numbers of large blues. 

“Creating the right conditions for this globally endangered butterfly to not only survive but to hopefully thrive has been the culmination of many years' work. None of this would’ve been possible without the combined efforts of conservationists and the local graziers."