Common Blue Lycaenidae

Polyommatus icarus (Rottemburg, 1775)

Description: Wingspan 29-38mm. Males and females differ. The males are a vivid violet blue on the upperside with a prominent white fringe along the margins of both wings. The females are dark and the blue colour is less extensive, though this is prone to some variation. The rest of the upperside is brown with a series of orange spots along the outer margin. The undersides, which are similar in both sexes, are grey-brown marked with black centred white spots and large triangular orange spots along the margins.

Similar Species: This is the commonest blue in N. Ireland and the only blue-coloured butterfly likely to be seen in open habitats. Identification is easily confirmed by looking for the orange spots on the underside which is not shown by the only similar butterfly, the Holly Blue. Also the Holly Blue is a woodland species and has an earlier flight period than this species.

Key Identification Features:

Sets:  male upperside male underside female upperside female underside

Flight Period: Univoltine in N. Ireland flying from June to August.

Status: This is a common species on the coast. Inland it is largely confined to grassland on well-drained soils such as the limestone hills in Fermanagh and Armagh and the chalk and basalt in Antrim. Consequently it is rare or absent in much of Tyrone, Londonderry and Antrim which are underlain by acid rocks or are poorly drained uplands.

Ecology: Occurs in loose colonies. These are found in open habitats including sand dunes, calcareous grassland, cuttings and abandoned quarries. Occasionally in damper sites and heaths. Males fly low over vegetation searching for females. Females once mated lay eggs on leaves of foodplant choosing isolated plants in open areas. In N. Ireland Common Bird's-foot Trefoil Lotus corniculatus is the principal foodplant in dry grassland but it may use related plants including Large Bird's-foot Trefoil L. pedunculatus on wetter sites. The larvae overwinter in third instar.

World Distribution: Found in the whole of Europe, in North Africa and across temperate Asia.

Bradley & Fletcher number: 1574 Agassiz number: 61.018

Additional information:

UK Butterflies account


 Thompson, R. S. & Nelson, B., 2003 (Oct 2). [In] The Butterflies and Moths of Northern Ireland