Assessing the status of the marsh fritillary butterfly (Eurodryas aurinia): an example from Glamorgan, UK

Abstract

We surveyed populations of Eurodryas aurinia (a butterfly listed as ‘Threatened in Europe’) in Glamorgan (South Wales, UK). The survey may provide a model for similar work, which is urgently needed throughout the species' European range. For each colony, we established population size, vegetation types, and current management regimes. Populations were assessed using larval surveys, a method which has several advantages over conventional adult surveys. With approximately 35 local populations, Glamorgan is among the most important areas for E. aurinia in the UK, and is of importance in a European context. However, 15 local populations were under immediate threat from unfavourable management or industrial developments, and only seven populations were on Sites of Special Scientific Interest. Colonies showed a clustered pattern, and varied greatly in size: 50% supported 20 or fewer larval webs. Many of the small populations may be temporary offshoots of larger, more permanent populations nearby. The largest local populations occupied Molinia caerulea - Cirsium dissectum fen meadow habitats (National Vegetation Community M24), which were unmanaged, grazed by cattle, horses or ponies, or subject to periodic burning. Detailed local surveys such as this one, which assess the relative sizes of populations and the impact of current management practices, may be the best way to plan future conservation measures for E. aurinia.