Farmers and conservationist alike must adapt quickly to the extreme weather events that we have regularly experienced over the last ten years.
At the time of writing this article (February 2014), the Somerset levels, which can be clearly seen from Collard Hill, resemble an inland sea, the army have been deployed to help the emergency services rescue local residents from their houses, politicians are donning waders for photo-shoots and everyone seems to have a theory as to who should shoulder the blame.
A quick search on the Met Office website confirms that we are indeed in unchartered waters:
Spring 2012 – drought with hosepipe bans
Summer 2012 – wettest summer for 100 years
Autumn 2012 – wettest Autumn since records began
Spring 2013 – coldest for 50 years
Summer 2013 – 7th hottest and 16th driest since records began
January 2014 – wettest January since records began
The Large blue butterfly, like all other wildlife, must negotiate a way through this meteorological hiatus and adapt accordingly, or perish! In 2012 the population increased for the eighth year in a row and nearly 50,000 eggs were laid on Collard Hill. However, detailed scientific research undertaken by Oxford University and the Centre for Ecology and Hydrology has shown that Myrmica ants do not prosper during cold springs which prevent them from foraging and collecting food to feed their grubs, which are the staple diet of the Large blue caterpillar. In a particularly long cold spring, like in 2013, the ants begin to starve and will eat their own grubs and any caterpillars that are living in their nest!
I have been fortunate to be working on a piece of research with Sarah Meredith (funded by Oxford University and The People’s Trust for endangered Species), exploring the synchronicity between the flowering of Wild thyme and the emergence of the Large blue. Because the butterfly will only lay its eggs on young tight flower-buds, it is vital that they emerge when the majority of the flowers are in the right condition. For the last three years Sarah has been monitoring the flowering phenology of the Thyme on Collard every 4 or 5 days between Mid May and the end of July and carrying out butterfly transects at the same time.
Since the early 2000s Large blues have emerged on Collard during the last week of May but in 2013 the first was seen on 14th of June, over two weeks late. Encouragingly the Thyme was also late to flower so the synchronicity between food-plant and butterfly was maintained. The cold spring did have a major impact on the size of the Large blue population and egg surveys revealed that the number of eggs laid on the site was just over 24,000, about half of 2012’s total. This trend was replicated across all monitored populations in Somerset and, although disappointing, is what happens to populations under adverse climatic conditions. Thankfully, because the management at Collard has been so good, a 50% drop in a large population is not catastrophic and I fully expect Large blues to be flying in good numbers in 2014.
The National Trust Rangers, Hayley Dorrington and Ian Clemett, together with Pat Burroughs the grazier had delivered perfect grazing on the site and once again organized signage and volunteer wardens to welcome the hundreds of visitors who came to see the butterfly. The site has been improved by excellent scrub management, carried out by NT staff and contractors, and partially funded by SITA under the Butterfly Conservation led project Expanding the Large Blue Landscape in the Polden Hills. Additional scrub was cleared by the generous efforts of volunteers recruited and encouraged by Butterfly Conservation’s Caroline Kelly and Rachel Jones. It is the combined efforts of all these people that have ensured that the prospects for Large blues on Collard in June 2014 are good.
Finally I must pay tribute to the late Barry Hillier who recently passed away. Barry volunteered for the National Trust and put in a huge amount of effort and will be remembered by many as one of the volunteers who helped visitors to Collard to see the Large blue and to understand their remarkable ecology. I will miss his kindness, knowledge and great sense of humour.
By David Simcox