Our summer workday at Common Wood had a focus on clearing bracken encroachment for the benefit of Marsh Fritillary butterflies. These threatened butterflies require areas of flower rich wet grassland, called rhos pastures, with a plentiful supply of devil’s-bit scabious, which is the food plant of their caterpillar. One of six fritillary species found on Dartmoor, the Marsh Fritillary is a focus for conservation, having suffered severe declines in recent decades.
6 DPA Conservation Volunteers were joined by 3 corporate volunteers from Babcock International, who were released from work for a day to volunteer within the local community. The morning was spent working on the lower, marshy area of the site, with volunteers requiring wellies to access the marshy pasture. Volunteers cut back a sizeable section of bracken, making a big impact, despite the unwelcome attention of hundreds of midges. In order to diminish the vigor of bracken, cuts must be carried out repeatedly, over a number of years, as this fast growing plant has an ability to store nutrients underground, which help it to bounce back from damage. Too much bracken in this area of precious rhos pasture risks shading out and out-competing slower growing wild flowers, including the devil’s-bit scabious which Marsh Fritillary caterpillars feed on.
Marsh Fritillaries are brightly coloured, with a mosaic of orange, yellow, and brown markings on the upper surface of both the forewings and hindwings, which form distinct rows of the same colour. Adult butterflies can be spotted flying from the middle of May to the end of June, with the males setting up small territories around a favoured perching spot. After mating, female butterflies will seek out a devil’s-bit scabious plant and lay a batch of up to 300 eggs. As soon as the caterpillars hatch, they create a protective web to help hide themselves from predators, and continue to eat the leaves of the scabious plant. By late summer the caterpillars are half-grown and they build a new communal web, where they overwinter together until around March, when they emerge to bask in the sun and continue feeding. When fully grown, the caterpillars are about 35mm long, almost black, and covered in spikes and small white spots. After pupating in a colourful chrysalis, they emerge as a new generation of adult butterflies.
Following bracken clearance on the lower part of the site, the group turned their attention to the upper site, which is much dryer and home to a population of Small Pearl Bordered Fritillary butterflies. Volunteers worked using slashers and loppers to create additional paths through the bracken and clear grassy areas within the scrubland for butterflies to fly. The plan was to shape an overall mosaic of habitat, including open grassy areas, swathes of bracken, paths with trampled edges, patches of gorse and some trees, as advised by Jenny Plackett of Butterfly Conservation. The trampled edges to the paths are particularly important, meaning there is dry brash for Fritillary caterpillars to overwinter in.
After lunch, ponies from the field above Common Wood wandered down to see what was happening, and quickly set about testing the new paths through the bracken. It is hoped that their movements will provide further natural trampling action, opening up small patches in the bracken, which allow light in so that Common Dog Violets can grow. These are the preferred food plant of the caterpillars of the Small Pearl Bordered Fritillary, and needed to nourish them over the winter and early spring.
While onsite, volunteers also aimed to carry out a butterfly survey, but did not identify any Fritillary butterflies flying on this occasion, although these butterflies have been seen onsite at Common Wood in previous years. Undeterred, one volunteer did spot a Small Pearl Bordered Fritillary while walking back to their car, so it’s good to know they are active in the area. The hard working team were all invited for tea and cakes when they had finished for the day, courtesy of the owner of the cottage by the entrance to the site.
If you’re feeling inspired by the success of our Conservation Volunteers, why not join them? The DPA host regular workdays and we’re always looking to recruit more volunteers for our friendly team. All training and tools are provided, plus there are plenty of coffee breaks and jobs for all abilities. Find a full list of upcoming workdays on our website.
Images: Sylvia Hamilton