Background
Insect Decline
Insects are disappearing worldwide at an alarming rate. These creatures, which make up more than half of all known species, provide essential ecosystem services like pollination, soil enrichment, and pest control. European butterflies have been particularly hard hit, with many species struggling to survive due to changing weather patterns and habitat loss.
The marsh fritillary (Euphydryas aurinia) exemplifies this trend. Once common across Europe, this species has experienced such severe declines that it’s now classified as vulnerable in Sweden.
Current Status and Climate Threats
On mainland Sweden, marsh fritillaries now survive mainly in power line corridors and forest clearcuts. The species remains more abundant on Gotland and Öland, where traditional landscapes persist.
However, these areas are also threathened. The 2018 drought drastically affected the butterfly’s host plant (Succisa pratensis) across the landscape, causing significant population crashes. This event demonstrated how climate extremes can rapidly undo conservation progress and highlighted the urgent need to understand what habitat conditions these butterflies require.
Understanding marsh fritillary habitat needs extends beyond saving one species—it’s about preserving entire grassland ecosystems. This butterfly serves as an indicator of grassland health, and supporting marsh fritillaries also benefits numerous other plants, insects, and wildlife. As Sweden balances agricultural productivity with conservation goals, this research provides the scientific foundation for informed land management decisions that can help threatened species recover while maintaining the landscapes that define Sweden’s natural heritage.
Aims
The aim of this study is to investigate the population size of E. aurinia using a catch-mark-recapture (CMR) and larvae nest inventory and to assess the population size in 2024 in comparison to previous years. Additionally, the study seeks to examine the effects of various habitat factors, such as ground moisture, ground temperature and bush cover on butterfly population size across temporal and spatial scales. Understanding which habitat factors have the greatest impact on the population and population trends over time is crucial to deepen the understanding of how changes in climate affect the species and to provide recommendations for future management.