Regional Species


Holly Blue
Celastrina argiolus

Photograph by Janet Graham (Harlech Forest)

Regional Species

This butterfly is usually seen in lowland districts, flying around trees and shrubs at, or above, head height. It is not unusual to see the butterflies flying high in the canopies of mature oak trees, in which situation they can be confused with Purple Hairstreaks.

The butterfly is bivoltine with the spring brood laying on holly and the autumn brood on ivy. The winter months are passed in the pupal stage.

The species is well known for experiencing a cyclic variation in population size and this phenomenon has been very noticeable in North Wales over last few years. In the late 1990s numbers were exceptionally high and the butterfly was a common sight even in areas where it had not previously been recorded. Indeed, there were even sightings of individuals flying across open moorland. In contrast, since the turn of the millennium numbers have crashed and there have been few recent records. Presumably the butterfly can still be found in coastal villages and hopefully it won’t be too long before we witness another population explosion.

The Holly Blue is not difficult to identify due to the pale, almost unspotted underside and the habit of flying higher than other blues. In March and April this is the only blue butterfly on the wing.