| Family | Lycaenidae |
|---|---|
| Subfamily | Polyommatinae |
| Genus | Phengaris |
| Species | nausithous |
| Authority | (Bergsträsser, 1779) |
| English Name | Dusky Large Blue |
| European Red List 2010 | Near Threatened (NT) |
|---|---|
| EU 27 Red List 2010 | Near Threatened (NT) |
| European Red List 2025 | Near Threatened (NT) |
| EU 27 Red List 2025 | Near Threatened (NT) |
| Habitats Directive | HD II IV |
| Bern Convention | BC II |
| CITES |
The Dusky Large Blue occurs on damp, moderately nutrient-rich grassland and rough vegetation. The butterflies are usually found on or near the foodplant Great Burnet (Sanguisorba officinalis). Having lived on the flowerheads of this plant for a few weeks, the small caterpillars go down to the ground, in order to be carried away by workers of the ant Myrmica rubra to an ant nest. There, they remain feeding on ant grubs, hibernating and pupating in the early summer. The newly-emerged butterflies leave the nest. The Dusky Large Blue is one of the most specialized of the “ant blues” being most adapted to one species of host ant. It is single-brooded.
Austria / Belarus / Bulgaria / Croatia / Czechia / France / France: Mainland / Germany / Hungary / Liechtenstein / Netherlands / Poland / Romania / European Russia / Slovakia / Slovenia / Spain / Spain: Mainland / Switzerland / Ukraine /