Large blue butterfly spreads wings again in Cotswolds after 150 years

The large blue butterfly is flying again over the hills of England where it hasn’t been seen in 150 years.

Conservationists are hailing the success of a project launched last year to try and bring the species back to Britain.

Around 1,100 larvae were released last autumn in Gloucestershire and this summer the sight of roughly 750 butterflies filled the sky.

But that’s only half the story. Before the larvae could be planted, experts undertook five years of grassland management to make sure the habitat was suitable to reintroduce the species.

This painstaking work is being heralded as the most successful insect reintroduction worldwide. The large blue butterfly is endangered around the world but now flies in greater numbers here in the UK than anywhere else.

Large blues are very fussy insects and require an extremely specific species of ant to eat as well as wild thyme and marjoram in which to lay their eggs.

The ground they occupy also has to be grazed by cattle to provide them with the correct environment.

Electric fences were deployed on Rodborough Common in the Cotswolds to persuade several different traditional breeds of cattle to graze on suitable areas of sloping land before the larvae were released.

‘With a wingspan of more than two inches, the large blue is the largest and rarest of all nine British blue butterflies. It was last recorded at Minchinhampton and Rodborough Commons 150 years ago and was declared extinct in Britain in 1979,’ explained the National Trust.

‘The butterfly was then re-introduced from continental Europe as part of a long-term conservation project nearly forty years ago and since then has established a stronghold at several core sites and has naturally colonised others across southern England.’

David Simcox, research ecologist and co-author of the commons management plan added: ‘The butterfly needs high densities of the heat-loving red ant, Myrmica sabuleti which has a crucial role to play in the lifecycle of the butterfly.

‘The grazing cows create the ideal conditions for them by keeping the grass down so sunlight can reach the soil which gently warms it creating perfect conditions for the ants, which are cold-blooded and therefore need warmth in order to actively scout for food throughout the spring, summer and autumn.

‘Then, in the summer when the ants are out foraging, nature performs a very neat trick – the ants are deceived into thinking that the parasitic larva 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 herbivore to carnivore, feeding on ant grubs throughout the autumn and spring until it is ready to pupate and emerge the following summer.’

Julian Bendle, Conservation Officer for the Back from the Brink project and Butterfly Conservation said: ‘Bringing such an important and rare species back to Rodborough Common is a testament to what collaborations between organisations and individuals can achieve. Creating the right conditions has been vital to the programme and this doesn’t happen overnight.’

Richard Evans, Area Ranger for the Commons, added: ‘Butterflies are such sensitive creatures, and with the large blue’s particular requirements they are real barometers for what is happening with our environment and the changing climate.

‘Large blues were once a common sight on the commons but some of the grassy slopes had become overgrown which had a severe impact on the red ant’s habitat. The long grass and scrub had caused the soil to cool which made it difficult for the ants to survive. As the ant population dwindled in the late nineteenth century, so did the numbers of large blues

‘Creating the right conditions for this globally endangered butterfly to not only survive but to hopefully thrive has been the culmination of many years work. None of this would’ve been possible without the combined efforts of conservationists and the local graziers.’

Just over forty years ago the large blue was declared extinct in the UK – but now, thanks to conservation work across Southern England, the future looks promising for the species.

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