Scarce Large Blue

The Scarce Large Blue (Phengaris teleius) 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 mainly mesotrophic moist meadows characterised by an abundance of the larval host plant Greater Burnet (Sanguisorba officinalis). Adults fly in a single generation in July and August. Females deposit eggs into the flowerheads of the Great Burnet, where caterpillars develop for a few weeks by feeding on seeds. Larvae then descend to ground and await for being adopted by ant workers (Myrmica sp.). The caterpillars produce specific host ant’s pheromones, which prevent the caterpillars from being attacked by the ants, even when they start to feed on the host ant’s own brood. The larvae spend the rest of their lives below ground in ants’ nests where they also pupate.

The Scarce Large Blue occurs very localy on Ljubljana Marsh, mainly in its western part. The major threats to the species on Ljubljana Marsh are: early and frequent mowing (2–3 times/year); mowing the entire grassland in a single year; intensive grazing; fertilisation and ploughing of wet meadows; regular cleaning of drainage ditches and depositing the excavated material on the grassland surface along the ditch.

Scarce Large Blue (Phengaris teleius), Photo: Čelik T.