The globally endangered large blue butterfly has been successfully reintroduced at Rodborough Common in Gloucestershire in efforts to halt the worldwide decline of this special insect.
The project marks the largest ever reintroduction of large blues in the UK with 1,100 larvae released on the 351 hectare (867 acre) site last August after five years of prepping the commons for their return. An estimated 750 butterflies successfully emerged on the site over the summer.
The commons, which are Sites of Special Scientific Interest and a Special Area of Conservation, were selected for release because they support all of the key elements and habitat required by the butterfly. As well as supporting fourteen species of orchid and the rare pasqueflower, the calcareous grassland is also home to a large number of rare and endangered insects including the duke of burgundy butterfly and rock rose pot beetle.
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 Common 150 years ago and was declared extinct in Britain in 1979. 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.
Partners worked together to create the right conditions for the butterfly’s survival including the introduction of an innovative grazing regime and programme of scrub control. Small, temporary grazing areas were created by using electric fences. This allowed cows, including Luing, Hereford and Long-horn cattle, to graze some of the slopes that were traditionally less attractive to the free roaming cattle throughout the year. The combination of restricted targeted grazing and scrub control provided the right conditions for the Myrmica sabuleti ant which is vital for the butterfly’s success, as well as encouraging growth of wild thyme and marjoram where the butterfly likes to lay its eggs. These are also the main source of food for the butterflies.