After dramatic declines caused by land-use change, the Marsh Fritillary is protected across Europe (EU Habitats Directive, Annex II) and is considered critically endangered in Germany. One of the last stable populations is found in the Niederwerdenfelser Land, a biodiversity hotspot in the Bavarian pre-alps. Here, the Marsh Fritillary inhabits a wide range of habitats, from wet grasslands and fens to dry areas such as calcareous grasslands. The “Buckelwiesen” (hummocky meadows) – calcareous grasslands with small-scale variations due to pits and mounds – play a particularly important role. This species-rich habitat has also largely disappeared over the past century. To ensure the long-term survival of the Marsh Fritillary population, a research project supported by the “Federal Biological Diversity Programme” was initiated. The goal of our project is to expand the knowledge of the butterfly’s ecology and to support the species through the restoration of its unique habitat.