Holly Blue (Celastrina argiolus)
C. argiolus is primarily found in the southern half of the British Isles and is a frequent visitor to gardens, churchyards and parks. This species is renowned for fluctuating in numbers, forming a predictable cycle over several seasons, thought to be caused by the abundance of the parasitic wasp Listrodomus nycthemerus whose sole host is the Holly Blue. The wasp lays its eggs in the larvae of C. argiolous, with a single adult wasp eventually emerging from the pupa. In England and Wales this species is widespread and common, south of a line running from Cumberland in the west to County Durham in the east. It is also found on the Isle of Man and throughout Ireland, but is absent from Scotland except as a scarce vagrant.
There are two broods each year, although there may be only one brood in the north. Adults from overwintering pupae emerge as early as the first week of April in a typical season, with the next generation emerging during mid July and early August. The three images above are of summer brood individuals. The first two pictures depict the same male. The third image is a female nectaring on bramble blossom.