Marsh fritillary

The Marsh firtillary (Euphydryas aurinia) is a threatened European butterfly species, and protected by the Habitats Directive and Bern Convention. In slovenia the species and its habitats are protected by law.

The species’ habitats on Ljubljana Marsh are alkaline fens and oligotrophic (non-fertilised) wet meadows with Purple Moorgrass (Molinia caerulea). Adults fly in a single generation in May and June. They are not selective regarding nectar plants. But, as larval habitats are usually very pure with nectar plant species, they need additional food in the nearby grasslands. Female lays eggs in a batch of cca. 250 (600) eggs on the under-side of a leaf of Devil’s-bit Scabious (Succisa pratensis). Large and sun exposed leaves of branched Succisa plants growing in large and dense stands and surrounded by lower vegetation are prefered by egg-laying females. After hatching, larvae spin a silken nest around the food plant (Succisa pratensis). Caterpillars feed and bask gregariously during sunny days until September, when they enter a hibernation in a collective compact and water-proof winter nest on host-plant. In March they start feeding and basking collectively, and become solitary owing to the increase in their food needs. The pupate on stems or leaves in herb vegetation.

In the last century, the species occured mainly in the southeastern part of Ljubljana Marsh. Five years ago, the Marsh fritillary was observed on Ljubljansko barje for the last time, on the alkaline fen in a small forest valley near Gorenje Blato. The major factor that led to extinction of the population in this site is the destruction of habitat caused by a drainage ditch which was dug across the entire width of the habitat before 2001. This resulted in fast overgrowing of the fen with Alder buckthorn (Frangula alnus) and Common reed (Phragmites australis). The draining has enabled further interventions, such as intensification of land use in the close vicinity of the fen, and enlargement of a path across the habitat to the surrounding forest. The key reasons which prevent species survival in other parts of Ljubljana Marsh are above all: early mowing (June, July) and baling of hay; mowing the entire grassland in a single year; intensive grazing; fertilisation, ploughing and burning of wet grasslands; regular cleaning of drainage ditches and depositing the excavated material on the grassland surface along the ditch.

Marsh fritillary (Euphydryas aurinia), Photo: Čelik T.