In 2000, after several years of working with the National Trust to get the grazing right, we were able to re-introduce the Large blue to Collard Hill with 267 caterpillars and 14 female butterflies from the nearby Somerset Wildlife Trust site of Green Down. Bizarrely, when they emerged the following year the country was in lockdown, owing to Foot and Mouth disease, and the site we had always planned as a public access site was closed!
When the first Large blue egg is laid in 2020, it will be part of the 20th generation and, at the time of writing (8th May), it seems likely that the site could again be inaccessible to all but the locals. Please check this blog regularly for updates regarding advice about visiting the site.
Every year we survey the distribution and egg numbers on Collard so we can produce a scientific estimate of the population. The graph above shows that in 2018, following excellent management and a warm spring, record numbers were found on the site. However, July 2018 fell into drought and we knew this would impact on the survival of caterpillars and their host ants. As expected, the population on Collard fell quite dramatically in 2019 but to very respectable numbers still ranking it is the 3rd largest known population of Large blues anywhere in the world.
Prospects for 2020
I was able to visit Collard on 7th May to assess grazing levels and was pleased to see that, despite a very wet winter and record-breaking warm April, the site is looking in excellent condition. My visit coincided with the brilliant white blossoms of Hawthorn across the site.
One of the main reasons that the Large blue population continues to thrive here is due to our excellent grazier, Pat Bishop, and her small herd of Dexter cattle, augmented by a few retired riding school ponies.
The cattle and ponies ensure that the turf height is short in both the spring and late summer ensuring that the soil is warm and conditions are right for the Red ant Myrmica sabuleti which the butterfly needs to survive.
Given the very dry April this year, I was delighted that the rain which fell at the very end of the month had allowed the Wild Thyme to remain green and continue to grow. The ant hill above is literally enveloped by Thyme and within a few weeks will produce pink flowers that will hopefully be visited by egg-laying Large blue females.
Provided the site has some rain over the course of the next three weeks, there should be good numbers of Large blues flying across this beautiful site again.
Before you consider travelling to Collard this year please check the Large Blue Blog and follow the rules and advice displayed here.
David Simcox (Large Blue Project Officer)
9th May 2020
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.