Four decades of hard labour and Battenburg cake: what it takes to bring the large blue butterfly back to Britain

Conservationists led by Sir David Attenborough will pay tribute to the remarkably successful reintroduction of the large blue

Patrick Barkham, guardian.co.uk 16 Jun 09;

Ants, Battenberg cake and 37 years of heroic labour by one scientist will be celebrated today as the ingredients that brought the large blue butterfly back from the dead.
Photograph: David Simcox/National Trust/PA

This rare and mysterious insect became extinct in Britain 30 years ago but conservationists, led by Sir David Attenborough, will pay tribute to its remarkably successful reintroduction by visiting grassland in Somerset where the butterfly now flies in larger numbers than anywhere else in western Europe.

The large blue was revived only after the endeavours of Jeremy Thomas, professor of ecology at the University of Oxford, who unravelled the butterfly's baffling lifecycle and masterminded its top-secret reintroduction using large blue eggs taken from the island of Öland in Sweden.

For decades, the large blue was greatly prized by butterfly collectors. Despite their best efforts to breed perfect specimens in captivity, they failed, and so they caught thousands of wild specimens which drove the species to extinction in parts of north Cornwall and the Cotswolds. But even after collecting was banned from sites, the butterfly continued to disappear.

When the butterfly was reduced to just two colonies in 1972, Thomas, who also works for the Centre for Ecology & Hydrology, was dispatched to live with the butterfly to solve the mystery of its decline.

In a race to save it from extinction, every summer for six years, he "measured everything", counting thousands of eggs, and laying trails of Battenberg cake to attract ants and locate their nests where, bizarrely, the large blue caterpillar spent most of its life. "It was a bit like a detective story," said Thomas.

Entomologists had already uncovered the large blue's dependence on ants but did not fully understand it. The large blue caterpillar drops to the ground after hatching and tricks ants into taking it into their nest by secreting a seductive fluid and even "singing" to the ants so they believe it is a queen ant grub. In the comfort of the nest, the parasitic caterpillar devours ant grubs all winter, pupating and emerging from the ground as a butterfly in June.

Crucially, Thomas discovered the large blue was only able to trick successfully one species of ant, Myrmica sabuleti. If it entered the nests of other ant species, the caterpillar was likely to be attacked and killed.

In research published in the journal Science, Thomas charted how the Myrmica sabuleti ant requires warm ground, only created by short, well-grazed grass, to survive. A near-imperceptible difference of just a centimetre in grass length could change the soil temperature by 2C-3C, causing the ant — and the large blue with it — to perish.

The widespread decline in grazing sheep and cattle and myxomatosis, which decimated wild rabbits after the 1950s, caused traditional grassland to grow too tall and cool for ant and butterfly.

Thomas's discovery was just too late to save Britain's last population of large blues, which died out in 1979. Undeterred, he and David Simcox, his colleague at the Centre for Ecology & Hydrology, reintroduced the butterfly 25 years ago on a carefully restored and managed meadow in Devon known only as Site X. To this day, the location of Site X is still a closely guarded secret to thwart rogue butterfly collectors.

Now reintroduced to six other sites, the large blue has spread to a total of 28 colonies in the Polden Hills, Somerset. This includes one National Trust site, Collard Hill, which is now open to the public. The large blue can even be spotted from the train: some of its largest populations fly on railway embankments close to Castle Cary, Somerset, which are managed by Network Rail to encourage the butterfly. Other landowners who helped revive it are the Somerset Wildlife Trust and even the owners of Clark's shoes, based in nearby Street.

"The restoration of the large blue butterfly to Britain is a remarkable success story, illustrating the power of ecological research to reverse damaging environmental changes," said Sir David Attenborough. "It is, moreover, a tribute to the dedication of many practical conservationists who have skillfully recreated its specialised habitat in our countryside."

Martin Warren, chief executive of Butterfly Conservation, said Thomas's "painstaking" research was a "watershed moment" for conservation because it showed the importance of managing habitat after a mistaken focus on letting nature take its course during the 1970s. The Adonis blue, the silver-spotted skipper and the heath fritillary have all been saved from near extinction using ideas from Thomas's scientific research.

"[The research] was the turning point not just for the large blue but was a watershed moment for conservation because it showed the need for the management of habitat to conserve rare species," said Warren.

Praising the labours of Simcox, and landowners such as Network Rail, Thomas said the success showed that other rare insects could brought back from the brink . "Up until then, everything had failed. There was very little insect conservation being attempted," he said. "It is a practical demonstration that it can be done with a species of butterfly or insect elsewhere in the world."