The male upper side is bright violet-blue with narrow dark-blue margins and chequered borders. The female upper side is usually a sky-blue with much wider dark-blue margins. Wingspan 35mm.
The caterpillars feed on Holly in the main, also Dogwood, Spindle, Gorse, Bell Heather, Bramble, Raspberry, Hop, and many other herbaceous plants and shrubs. Ivy is usually the second broods’ main food source. The caterpillar has a special relationship with ants, and the pupae are also attended by them.
It flies April to September in two broods. Found in open woods and woodland margins, hedgerows, and parks and gardens. Apart from the Long-tailed Blue, it is the only other European blue to be seen high up in the trees, mainly feeding on sap and honeydew. Seen all over Britain except Scotland, and is common and resident.
Photographs of female Holly Blue (Celastrina argiolus) taken April 2006, rear garden, Staffordshire. © Pete Hillman 2006. Cameras used Sony Cyber-shot DSC-W1.