The marsh fritillary butterfly is distributed across Europe, but listed as ‘vulnerable’ throughout it’s range. In the UK, there are only six regional strongholds for this butterfly, Devon and Cornwall being one of them, which makes our Dartmoor populations so precious.
The marsh fritillary makes its home in a range of damp grassland habitats, and have a complex life cycle. The adults emerge in late May to early July, and fly for only a few weeks. They seek out Devil’s bit scabious to lay their bright yellow clusters of up to 350 eggs. The eggs hatch in August and live as a colony, spinning a protective web amongst the grass, from which they emerge to eat the scabious. In the following spring the caterpillars will pupate, ready to emerge as adults in summer.
The marsh fritillary lives as metapopulations, meaning that several sub-populations will occur in one geographical area. In any particular year, the sub-population at any given site may fluctuate greatly. Adult butterflies generally do not disperse far, but these sub-populations are linked through occasional dispersal, and are therefore reliant on eachother’s existence for the overall health of the population.
The Tavy valley, from Peter Tavy to Standon Hill form one of these metapopulations, with sub-populations establishing everywhere there is suitable vegetation. An ideal site has plentiful Devil’s bit scabious, as well as a range of other herbs for the adults to feed on, plus grassy tussocks for the caterpillars to hibernate in. Low intensity cattle or pony grazing works best to create these ideal conditions. Achieving the perfect level of management is a balancing act – too much grazing results in the loss of scabious and tussocks – too little grazing and the tussocky grass and bracken take over and smother the scabious and other herbs. At Common Wood, DPA volunteers clear away encroaching bracken to maintain the open habitat.
Each year, Devon Wildlife Trust and Butterfly Conservation, with the help of local volunteers, monitor populations. They provide free advice to landowners on how to best manage habitats for the marsh fritillary, and can assist with seeking grant funding to restore habitats. They’d love to hear from you if you spot any marsh fritillary butterflies in the area, or if you’d like to discuss habitat management to ensure survival of this beautiful species.
Contact: Rachel Kaleta. DWT Farm Advisor rkaleta@devonwildlifetrust.org