Whilst Jeremy Thomas and I were rearing Large blue caterpillars for an experimental introduction to Collard Hill, Kevin Keegan was coaching the England football team towards an early exit from the European Championship, Tony Blair was Prime Minister and petrol was 76pence per litre. It was the year 2000 and millennium fever was upon us.
We had spent the previous four years working with the National Trust to ensure that the site was as suitable as possible to receive this fussy butterfly. We were able to collect eggs from the Somerset Wildlife Trust’s nature reserve, Green Down, where the butterfly had already begun to adapt to the UK climate rather than the Swedish one from where they had originated in 1992. Like all Large blue introductions, this one involved rearing caterpillars in individual boxes (they are cannibalistic), over a four week period and making daily trips to the site each evening to put down the caterpillars that had become ready for ant ‘adoption’ during the afternoon of that day.
Then there was an eleven-month wait. Long before any butterflies emerged our attempts to check management on the site were thwarted by the onset of a national outbreak of Foot and Mouth disease. After careful negotiation with the local farmers and having made solemn promises to disinfect ourselves (a pervasive smell that was to linger until autumn), we were eventually able to visit the site. Despite the restrictions on livestock movements Collard was looking the best we had ever seen and our confidence began to grow.
On June 5th 2001, I saw 4 different Large blues flying including an egg laying female and all the signs were good. At that time the breeding area was relatively small and almost entirely confined to the south eastern part of the site as Wild thyme was sparse or absent over the rest of the site. Over the course of the next few years the National Trust propagated and planted out several thousands of plants and wrestled to get to grips with the grazing.
The red ant, Myrmica sabuleti, which is parasitised by the Large blue is a heat-loving ant and will only prosper when the hill is grazed short in the spring and late summer and this proved very difficult to deliver. After much debate, NT were able to fence off the large flat area at the top of the site to create an area of layback land where animals could be moved to prevent overgrazing at critical times of the year.
Grazing is fundamental to correctly managing a Large blue site and we have been incredibly lucky with our graziers Pat and Martin and their herd of Dexter cattle, supplemented by some of their retired riding ponies. They have delivered the perfect conditions for many years and are always happy to move animals at short notice.
Pat and Martin’s Dexter cattle. Fence to layback field on left of picture.
Scrub management has also been crucial to achieving a fine balance of beneficial scrub, which provides shelter on a windy day, and preventing the rich limestone flora from being shaded out. This work is undertaken by NT staff and volunteers helped by partnership organisations the Somerset Wildlife Trust, Butterfly Conservation and the Clark Trust.
Over the last five years the project has been helped with funding from Biffa and SITA in a Butterfly Conservation led project to help the butterfly to expand across the Polden Hills landscape.
Each year Jeremy, Sarah Meredith (Large Blue Collard Ranger 2010) and myself carry out detailed egg surveys at Collard and the fortunes of the colony can be seen in the graph below. The population endured a large decline after the very cold spring of 2013, which impacted badly on the ants, and the searing July temperatures of the same year that desiccated the caterpillar food-plants leading to high mortalities and a poor emergence in 2014. This was a pattern that affected all sites in Somerset. However, owing to the excellent habitat management here record numbers of eggs were laid in 2015 which bodes well for the 2016 season. It is a huge credit to everyone involved with Collard that since 2001 the area of suitable Large blue habitat has increased from 0.7ha to 3.3ha.
David Simcox (Large Blue Project Officer)
The Large Blue Project is underpinned by science, carried out by Oxford University and CEH and implemented by a collaborative partnership between Butterfly Conservation, CEH, Gloucestershire Wildlife Trust, J&F Clark Trust, National Trust, Natural England, Network Rail, Oxford University, Somerset Wildlife Trust, South Somerset District Council and private landowners.