Rare large blue butterflies just experienced their most substantial reintroduction into the wild. About 750 of the globally endangered butterflies successfully hatched from larvae and flapped around Rodborough Common in Gloucestershire this summer.

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a blue butterfly with black spots on a blade of grass

“Bringing such an important and rare species back to Rodborough Common is a testament to what collaborations between organisations and individuals can achieve,” said conservation officer Julian Bendle in a press release issued by National Trust. “Creating the right conditions has been vital to the programme and this doesn’t happen overnight.”

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a blue butterfly with black spots on a blade of grass

Rodborough Common serves as both a Site of Special Scientific Interest and a Special Area of Conservation. Officials selected this area for the butterfly release because it met the species’ habitat requirements. The space houses several rare plants and insects, including the pasqueflower, duke of burgundy butterfly, rock rose pot beetle and fourteen different orchid species.

a gray, blue and white butterfly with black spots on a blade of grass

Of Britain’s nine types of blue butterflies, the large blue, with a wingspan surpassing two inches, remains the biggest and rarest. With no large blue sightings at Rodborough Common logged for 150 years, in 1979 officials declared the species extinct in Britain.

a blue butterfly on a gray mass surrounded by grass

Lepidopterologists began reintroducing the large blue from continental Europe nearly 40 years ago. The butterfly has now established populations at several sites across southern England. The campaign to bring the butterflies back to Rodborough Common took five years of planning and included changing the grazing patterns of local cattle, ensuring the butterflies had plenty of marjoram and wild thyme to lay their eggs in and providing an abundance of delicious red ants. This project also required many human partners, including people at the National Trust, Butterfly Conservation, the Limestone’s Living Legacies Back from the Brink project, Natural England, Royal Entomological Society (RES) and the Minchinhampton and Rodborough Committees of Commoners.

two blue butterflies with black spots perched together on a flower

As David Simcox, research ecologist and co-author of the commons management plan, explained, cows help the butterflies by creating “keeping the grass down so sunlight can reach the soil which gently warms it creating perfect conditions for the ants.” Simcox continues, saying, “Then, in the summer when the ants are out foraging, nature performs a very neat trick – the ants are deceived into thinking that the parasitic larva of the large blue is one of their own and carry it to their nest. It’s at this point that the caterpillar turns from herbivore to carnivore, feeding on ant grubs throughout the autumn and spring until it is ready to pupate and emerge the following summer.”

a blue butterfly with black markings perched on a red tree branch with green leaves

Last August, conservation groups released 1,100 larvae on the 867-acre site. The 750 resulting adult butterflies demonstrate the program’s success.

+ National Trust

Images via Sarah Meredith and David Simcox