Reintroducing the Large Blue

Large Blue butterflies disappeared from the UK in the 1970s. After a long absence, a successful collaboration between the National Trust, Butterfly Conservation, the Limestone's Living Legacies Back from the Brink project, Natural England, Royal Entomological Society and the Minchinhampton and Rodborough Committees of Commoners has seen them reintroduced back onto the commons. 

Building the foundations

An experimental conservation grazing scheme has been fundamental to the reintroduction with electric fences being used to contain some of the free-roaming cows. 

Grazing cattle were one piece of the jigsaw. Managing and controlling the scrub was the other. Together, the combination provided the perfect conditions for wild thyme and a tiny, but crucial species of red ant to flourish. 

Over several years, Dave Simcox, the ecologist that led the reintroduction, painstakingly carried out regular surveys of the ants and foodplants across the commons. The surveys provided the team with the evidence they needed - the commons could once again support populations of the Large Blue.  

Herbivore to carnivore

The Large Blue's entire existence depends on one species of tiny red ant, Myrmica sabultei. The unsuspecting ants are tricked into thinking that the parasitic larvae 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 harmless herbivore to cunning carnivore as it feeds on ant grubs until it's ready to pupate and emerge the following summer. 

Spotting a Large Blue

With a wingspan of more than two inches, the Large Blue is the largest and rarest of all British blue butterflies. It was once a common sight on the commons but some of the grassy slopes had become overgrown which affected the red ant's habitat. As the ant population dwindled in the late nineteenth century, so did the numbers of Large Blues.

It was declared extinct in Britain in 1979 but was reintroduced in the early 1980s as part of a long-term conservation project.

Turning the dream into reality

Successful collaborations have been key to the success of the reintroduction. Some of the caterpillars that were introduced came from Daneway Banks, a Cotswold site managed by Gloucestershire Wildlife Trust and the Royal Entomological Society. The Back from the Brink project and Butterfly Conservation supplied the materials and funded a contractor to construct the temporary grazing compartments. Back from the Brink funding from the National Lottery also enabled the captive rearing necessary to bring the butterfly back to the commons.