The great blue butterfly has had its best summer in Britain for 150 years thanks to targeted restoration work, benefiting other rare insects, including the shaggy oil beetle and the shrill maple bee.
The butterfly, which became extinct in Britain in 1979 but was reintroduced four years later via caterpillars from Sweden, flew in its greatest numbers since registration began in June this year.
South West England now supports the world’s largest known concentration of great blue species, listed as one of Europe’s most endangered insect species.
Up to a third of the UK’s population can be found in 12 new sites that a conservation partnership has restored to flowery farmland pastures, failed conifer plantations, railway embankments or degraded downland.
The new pasture under special management for large blue species also proves to be an ideal breeding ground for rare plants such as the extremely rare pasqueflower and 12 species of orchids, including musk orchid, autumn lady stresses and the large butterfly orchid.
Rare insects that have benefited include the shaggy oil beetle, the rock rose beetle, the shrill maple bee, the downland villa and the spotted beeflies, and eight endangered butterfly species, including the resurrecting Duke of Burgundy, once one of the most endangered species in the world. the UK.
The new pastures are managed or owned by six partner organizations – the National Trust, Somerset and Gloucestershire Wildlife Trusts, J & F Clark Trust, Natural England and the University of Oxford – with the restoration overseen by David Simcox and Sarah of the Royal Entomological Society Meredith.
Simcox said: “We are extremely proud that the partnership’s efforts have enabled hundreds of people to see this beautiful and enigmatic butterfly fly in some of the most beautiful grassland locations in the country.
“The biggest challenge for the future is to secure this expansion in a warming climate and to develop strategies to mitigate the effects of extreme weather events.”
The great blue has an extraordinary lifestyle: its young caterpillars trick ants into believing they are young ant larvae, and they are incorporated into ant nests. Here they are protected underground all winter and grow fat by devouring ant larvae.
The species went extinct in Britain because the cessation of grazing and rabbit grazing on traditional pastures left the grass too tall and temperatures too cold for the ant species to survive.
The butterfly’s lifestyle and requirements were worked out by Jeremy Thomas, now Professor Emeritus of Ecology at Oxford, who has led the butterfly’s reintroduction, with the ant species thriving again when pastures are grazed to an appropriate level.
Thanks to support from the Prince of Wales’ Charitable Fund, the butterfly has been reintroduced to two new sites in the Cotswolds over the past three years, but now conservation focus is turning to how to ensure the new populations can withstand warming from the earth.
Severe drought causes the ants to become malnourished, and if they are stressed, they are more likely to notice the deception of the big blue caterpillars and drive them off or devour them.
The butterfly’s population has declined after previous droughts, but Thomas said he hoped the worst of the dry weather hadn’t hit the Somerset and Cotswold sites.
The recovery sites have been deliberately chosen with a variety of microclimates and soil depths, so that most have areas that are too cool and moist for the ants and butterflies in most years, but are essential refuges during droughts.
Thomas added: “The unprecedented success of this project is a testament to what large-scale collaboration between conservationists, scientists and volunteers can achieve. Its greatest legacy is that it shows that we can reverse the decline of globally endangered species once we understand the drivers.”