Description: Wingspan 26-34mm. Males have lilac-blue upperwings. The outer fringe of hairs is chequered black and white. The underside is pale silvery blue with black spots. Females differ from males in having a broad black border to the upperside of the forewings. In N. Ireland the Holly Blue is univoltine flying from early April to June. In the south of Britain and Ireland the Holly Blue is bivoltine and this habit is apparently spreading north at least in Britain. The second brood flies from late July to September.

World Distribution: The Holly Blue is a very widespread Holarctic species and is present in the whole of Europe except most of northern Scandinavia, North Africa, Asia Minor and Central Asia, China, Japan and N. and Central America.

Irish Distribution: In N. Ireland the Holly Blue is confined to central and south Down especially in a triangle betweeen Newcastle, Carryduff and Comber and also the Rostrevor area. There have been records from several other areas but the only confirmed colony outside Co. Down is at Correl Glen in Fermanagh.

Ecology: Colonies of Holly Blue are found in open woodland, hedgerows and mature gardens which support its foodplants. In Britain and Ireland the principal foodplants are Holly Ilex aquifolium and Ivy Hedera helix. The spring brood feeds principally on Holly and the second brood mainly on Ivy. In N. Ireland where all populations are univoltine, Holly is probably the sole foodplant. The females lay eggs at the base of base of flowerbuds on plants growing in sunny warm conditions. The larvae feed on the developing flowers and fruit. It overwinters as a pupa.

Key Identification Features:

• Male has lilac-blue upperside
• Female has lilac-blue wings fringed with a broad black band on forewing.
• Silver blue underside with small black spots in both sexes
• Outer fringe of hairs chequered

Distribution Map from NBN: Celastrina argiolus at National Biodiversity Network mapping facility, data for UK.

iNaturalist: Celastrina argiolus at iNaturalist World Species Observations database.