The butterflies are back

One of Britain’s most threatened butterfly species has seen a surge in numbers this summer – offering fresh hope that a program designed to protect them is working. Recent surveys suggest that numbers of marsh fritillary butterflies in Dartmoor and Exmoor may be on the increase.

Butterflies can’t fly in the rain, which limits their ability to find nectar and breed, so there was a real concern that the dire conditions in 2007 and 2008 would have had a serious impact on numbers this year. The warm and sunny conditions throughout the spring and early summer encouraged good numbers on many sites across the moors, and marsh fritillaries – which fly from late May to the end of June – had an especially good year. Counts at some Dartmoor sites were two or three times higher than those recorded during the previous two years, while the only remaining marsh fritillary site on Exmoor also enjoyed strong numbers. Other rare fritillary butterflies have also had a promising year. The number of high brown fritillary on Dartmoor were almost double from last year, while the heath fritillary population on the western edge of Dartmoor had the second highest count since weekly recording began in 1994. Counts of the heath fritillary in Exmoor were also very positive.

Weather isn’t the only factor, though. The Two Moors Threatened Butterfly Project, lead by Butterfly Conservation in partnership with Dartmoor and Exmoor National Park Authorities, Natural England and the Environment Agency, has been working with landowners and land managers over the past four years to carry out management works to improve the butterflies’ habitat. Ideal habitat management for the butterfly is achieved through traditional farming practices, such as light grazing.

Jenny Plackett, Butterfly Conservation’s Project Officer, said “The marsh fritillary is one of Britain’s rarest butterflies, so it’s fantastic that this species seems to be making a real recovery on Dartmoor and Exmoor. The landowners are working really hard to improve conditions on their land for the butterfly, and it’s very encouraging that their efforts are now showing such positive results.”

Photo: Marsh fritillary by Norman Baldock, Dartmoor National Park Authority