The butterfly, which became extinct in Britain in 1979 but was reintroduced via caterpillars from Sweden four years later, flew in its highest numbers in June this year since records began. South West England now supports the largest known concentration of big blues in the world, which are listed as one of the most threatened insect species in Europe. Up to a third of its British population is found in 12 new sites which a conservation partnership has restored to flower-rich meadows from arable fields, failed conifer plantations, railway embankments or degraded areas. Female big blue lays her eggs. Photo: Jeremy Thomas/Royal Entomological Society The new meadow under special management for big blues also proves to be an ideal breeding ground for rare plants such as the extremely rare pascanth and 12 species of orchid, including musk orchid, autumn lady’s tresses and butterfly orchid. The rare insects that have benefited are the rough oil beetle, the scarab beetle, the screeching bee, the willow and spotted wagtails and eight threatened butterfly species, including the resurgent Duke of Burgundy, once one of the most threatened in the UK. The new meadows are managed or owned by six partner organizations – the National Trust, the Somerset and Gloucestershire Wildlife Trust, the J & F Clark Trust, Natural England and the University of Oxford – with the restoration overseen by David Simcox and Sarah Royal Entomological Society Meredith. Simcox said: “We are extremely proud that the partnership’s efforts have enabled hundreds of people to see this amazing and enigmatic butterfly in flight in some of the country’s most beautiful grassland locations. “The biggest challenge ahead is to ensure this expansion in a warming climate and to develop strategies to mitigate the effects of extreme weather events.” The big blue has an extraordinary lifestyle: its young caterpillars trick ants into thinking they are young ants and put them in ant nests. Here they shelter underground all winter and grow fat by devouring ant rods. A bumble bee at a restoration site in Somerset. Photo: Jeremy Thomas/Royal Entomological Society The species became extinct in Britain because the abandonment of grazing and rabbit grazing on traditional grasslands left the grass too long and the temperatures too cold for the ant species to survive. The butterfly’s lifestyle and requirements were worked out by Jeremy Thomas, now emeritus professor of ecology at Oxford, which led to its reintroduction, with the ant species thriving again when grasslands are grazed to the right level. Support from the Prince of Wales’s Charitable Trust has allowed the butterfly to be reintroduced to two new sites in the Cotswolds in the past three years, but now the conservation focus is on how to ensure new populations are resilient to global warming. Severe droughts cause ants to become malnourished and, when stressed, are more likely to spot the deception of the big blue caterpillars and chase them away or devour them. A young great blue caterpillar is adopted by an unsuspecting ant. Photo: Sarah Meredith/Royal Entomological Society The butterfly’s population has collapsed after previous years of drought, but Thomas said he was optimistic the worst of the dry weather had not affected the Somerset and Cotswold sites. Restoration sites have been purposefully selected with a variety of microclimates and soil depths, so that most have areas that are too cool and wet for the ant and butterfly most years, but are vital refuges during drought. Thomas added: “The unprecedented success of this project is testament to what large-scale collaboration between physiologists, scientists and volunteers can achieve. Its greatest legacy is that it shows that we can reverse the decline of globally threatened species once we understand the drivers.”
