Wingspan: 30–34 mm
Flight period: in one generation from June to August
Host plants of caterpillars: swamp gentian (Gentiana pneumonanthe)
The Alcon blue (Phengaris alcon or Maculinea alcon) is a large blue butterfly, whose grey-brown undersides of the wings are adorned with prominent white-edged spots in the middle of the wings and a series of scattered spots along the outer edge. The male has the upperside of the wings blue in color with a broad, almost black, outer margin. The central part of the upperside of the wings is without a pattern of black spots. The upperside of the wings in the female is more or less uniformly dark gray with a slight blue sheen along the body.
The Alcon blue lives in marsh meadows and low bogs, where swamp gentian grows and host ant species also live. It is found up to about 1000 m above sea level.
Even the larvae of the Alcon blue develop in ant nests, but they do not prey on the ants' brood. The worker ants feed the caterpillars and care for them just as they do for their own larvae.
Also this butterfly species is protected in Slovenia; in addition, as a threatened species (E) it is listed on the Slovenian Red List of endangered butterflies, because it is tied to human disturbances, it has extremely sensitive habitats and a highly specialized life cycle ... experts on this species have unfortunately found that in the last twenty years it has disappeared from a large part of the area of its former distribution...
