This Blue has a wing span of 20-31 cm. Its characteristic is the strong black spots, clear orange seam band and 4-5 metallic shining eye spots. But else the various Blues are much alike. The male of the Plebejus argus has a broad black seam with a "blurred" border towards the blue. The females are easier to recognize, since they are usually brown with a golden glow, while females of Ida's Blue (Plebejus idas) are more or less blue.
Elsewhere in Europe the argus females have often blue root fields. It is often necessary to use a magnifying glass to see if the argus has a small amber coloured prickle at the tip of the front legs. The Blue species can be difficult to recognize from one another in general, and I haven't used a magnifying glass, but there were many Plebejus argus in Lille Vildmose during this week, and this is one of them. A strong wind was teasing both the Blue and me!
Plebejus argus' flying period is from mid June till late August. Its habitats are heaths and dune-heaths with worn-out vegetation or new sprouts of heather. It overwinters as an egg, which is placed separately at low plants, and the larvae's fodder-plant is low or new sprouts of heather (Calluna vulgaris) and Bell heather ( Erica tetralix), but probably also other low plants.
It is found in spread populations all over Denmark, but is declining everywhere, especially on the islands. Extinct af the island Funen in 1989, but found in isolated populations in a few places on Zealand/Møn/Falster
Source : Michael Stoltze, "Dagsommerfugle i Danmark", 1997.
Photo Lille Vildmose 26 June 2010: grethe bachmann.