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.