Surge in butterfly numbers

The marsh fritillary, one of Britain’s most threatened butterflies has seen an unexpected surge in numbers this summer.

A Recent surveys suggest that numbers in Dartmoor and Exmoor may be on the up.

Marsh fritillary – Norman Baldock, Dartmoor National Park Authority

Marsh fritillary – Norman Baldock, Dartmoor National Park Authority

Following the declines noted during the last two very wet summers, the increase in numbers is offering fresh hope.

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.

However, the warm and sunny conditions throughout the spring and early summer encouraged good numbers of fritillary butterflies on many sites across the moors.

Marsh fritillaries, which fly from late May to the end of June, had an especially good year, with counts at some Dartmoor sites two or three times higher than those recorded during the previous two years.

The only remaining marsh fritillary site on Exmoor also enjoyed record numbers.

Butterfly project

However, this may not be only down to the weather! The Two Moors Threatened Butterfly Project, lead by Butterfly Conservation in a 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.

Specialist management advice has been given to landowners, and support provided to access funding towards the costs of management works such as scrub clearance and fencing.

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.”

Other rare fritillary butterflies have also had a promising year. Numbers of high brown fritillary recorded during weekly transect monitoring across known sites on Dartmoor are almost double those recorded in 2008, while the heath fritillary population on the western edge of Dartmoor had the second highest count since weekly recording began in 1994.

Timed counts of the heath fritillary in Exmoor were also very positive.

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