Best year for Britain's rarest butterfly since 1930s

Saturday 27th August 2016

Large Blue (c) David Simcox

The once-extinct large blue butterfly, reintroduced to the UK in 1984, flew in its highest numbers for at least 80 years this summer, belying widely-reported warnings that 2016 could be the worst year on record for British butterflies.

Thanks to meticulous conservation management, south-west England now supports the largest concentration of large blues known in the world. Gloucestershire Wildlife Trust and Royal Entomological Society’s Daneway Banks and Somerset Wildlife Trust’s Green Down saw over 10,000 adult large blues in 2016 according to Professor Jeremy Thomas, chair of the Joint Committee for the Restoration of the Large Blue Butterfly – which equates to roughly 60% of the UK population. Together they laid more than a quarter of a million eggs on the abundant thyme and marjoram flowers.

This is no mean feat, for the large blue is the only UK butterfly species that is sufficiently threatened worldwide to be listed in the IUCN’s global Red Data Book, and our only one designated as an ‘Endangered Species’ across Europe. The success of the large blue reintroduction is due to the combined efforts of the Large Blue Project. As well as the Wildlife Trusts in Gloucestershire and Somerset, partners include Natural England, Butterfly Conservation, the University of Oxford and the National Trust.

Gloucestershire Wildlife Trust’s CEO, Roger Mortlock, says: “This is fantastic news for this globally endangered butterfly whose extraordinary life cycle makes its conservation very challenging. Scrub clearance and careful grazing of wildflower-rich grasslands is key to ensuring a future for this beautiful insect. This special management also helps a huge diversity of wild plants and other insects to thrive.”

Professor Jeremy Thomas (Chair of the Royal Entomological Society’s Conservation committee, Emeritus Professor of Ecology at the University of Oxford, and chair of the Joint Committee for the Restoration of the Large Blue Butterfly) said:

"The success of this project is testimony to what large scale collaboration between conservationists, scientists and volunteers can achieve. Its greatest legacy is that it demonstrates that we can reverse the decline of globally-threatened species once we understand the driving factors."

The large blue has a bizarre life-cycle, having fed for three weeks on the flowerbuds of wild thyme or marjoram, the caterpillar produces scents and songs that trick red ants into believing it is one of their own grubs, and is carried underground into the ants nest and placed with the ant brood. The caterpillar spends the next 10 months feeding on the grubs before pupating in the nest the following year and then emerging to crawl above ground as a butterfly.

Despite over 50 years of effort to halt its decline, the large blue butterfly was pronounced extinct in Britain in 1979. Its reintroduction in 1984 was based on the discovery that large blue caterpillars can only survive in the nest of one particular species of red ant, Myrmica sabuleti. Changes in countryside management were responsible for the extinction. Alterations in grazing left grassland too tall and shady for the heat-loving red ant.

Reserves Manager for Somerset Wildlife Trust, Mark Green said: “The amazing numbers of Large Blues recorded this year show what can be achieved through close partnership working and landscape scale conservation land management, underpinned by sound science. Large blue numbers had declined significantly two years ago, due to unfavourable weather conditions. But, thanks to the project partners creating and maintaining a number of well-connected core sites, the butterfly has now bounced back to record numbers. I feel proud to play a part in this highly successful project, which gives me hope that we can reverse the declines of other vulnerable species.”

Today optimum habitat has been restored to more than 50 former sites. The finest of these are Daneway Banks Nature Reserve in the Cotswolds, and Green Down Nature Reserve in Somerset, both Wildlife Trust sites. Thanks to good gazing management coupled with favourable weather, their already massive large blue populations increased by 74% and 64% respectively compared with 2015. The National Trust’s Collard Hill site in Somerset also boasted good numbers, and remains the most accessible place to see large blues thanks to its extensive car park and on-site warden.

A spin-off of our managing grasslands to support the large blue is that it has simultaneously improved conditions for a diversity of other wildlife. 

At Daneway, scarce orchids including fly, frog and musk have returned after an absence of many years, and the exceedingly rare cut-leaved germander and cut-leaved self-heal are now flourishing. Among insects, the Downland Villa beefly – not recorded in the UK for 50 years prior to 2000 – bred in great abundance along the tracks and scrapings of Daneway in 2014-16.

At Green Down, cut-leaved self-heal also flowered abundantly in 2016, and meadow brown and marbled white butterflies had their highest and 2nd highest recorded numbers respectively in decades of recording, again belying predictions for low butterfly numbers elsewhere.


Contacts for further details or interviews

Prof Jeremy Thomas: Tel: 01258 880644
David Simcox: 01929 405164 / 07590 817474
Jenny Stevens: Tel: 01452 383333

Additional Notes

• The large blue was re-introduced to Devon in 1984, using an identical race to the extinct British one from Sweden, by Prof Jeremy Thomas and David Simcox after research by Thomas had identified the butterfly’s ecological needs. They made a further introduction to Somerset (Green Down) in 1992, where the butterfly thrived and spread across Somerset’s Polden Hills. In 2010, Green Down butterflies were used to re-establish the large blue in the Cotswolds, when it was re-introduced by David Simcox and Sarah Meredith to Daneway Banks, one of the four best historical large blue sites in Gloucestershire. The re-introductions to Devon and Somerset were led by the Centre for Ecology & Hydrology (CEH), part of the Natural Environment Research Council, and part-funded by Natural England, and to the Cotswolds by the University of Oxford and CEH, funded primarily by the EU Framework programme CLIMIT. Prof Jeremy Thomas chairs the national Joint Committee for the Restoration of the Large Blue Butterfly, with David Simcox serving as Project Officer and Sarah Meredith as Deputy Project Officer. The large blue project is underpinned by science carried out by Oxford University and CEH, implemented by a collaborative partnership between Butterfly Conservation, CEH, Gloucestershire wildlife Trust, J&F Clark Trust, National Trust, Natural England, NetworkRail, Somerset wildlife Trust, South Somerset District Council, Spalding Associates, and the University of Oxford.

• Gloucestershire Wildlife Trust is a countywide charity which manages 60 nature reserves covering over 2,000 acres in addition to identifying key sites of nature importance. Our aim is to secure a natural environment which the people of Gloucestershire and visitors to the area can enjoy for generations to come. We have a local membership of over 26,500 people and work with 500 regular volunteers who give their time to support the Trust’s work. Further information can be found on our website:

• The Royal Entomological Society is one of the oldest entomological societies in the world. Many eminent scientists of the past, including Charles Darwin and Alfred Russel Wallace, have been fellows. The Society organises regular meetings for insect scientists, as well as hosting international symposia and events for the public. It publishes journals and books as well as identification guides. The aim of the Society is “the improvement and diffusion of entomological science”.

• Supported by our members, Somerset Wildlife Trust has been protecting vulnerable wildlife and preserving wild places for over 50 years. We manage over 1,700 hectares of nature reserves, provide wildlife-friendly land management advice, campaign and educate to make sure Somerset remains one of the most wildlife-rich places in the UK. Our vision for the county is ‘an environment rich in wildlife for everyone.’ The Trust is one of 47 in the UK – together they make up the Royal Society of Wildlife Trusts (RSWT)

• The Wildlife Trusts is a network of 47 local Wildlife Trusts across the UK. Our vision is 'an environment richer in wildlife for everyone' and we're the largest UK charity dedicated to conserving all our habitats and species, with a membership of more than 800,000 people including 200,000 junior members. We campaign for the protection of wildlife and invest in the future by helping people of all ages to gain a greater appreciation and understanding of wildlife. Collectively, we manage more than 2,300 nature reserves spanning over 80,000 hectares. For further information about The Wildlife Trusts please telephone 0870 036 7711 or visit