Regional Species


Silver-studded Blue
Plebeius argus

Photograph by Janet Graham (Hafod Garregog)

Regional Species

More than one subspecies of this scarce butterfly occurs in North Wales.

* Ssp. caernensis is restricted to the Great Orme’s Head along with a few colonies elsewhere which are the result of deliberate introductions. The population density on the Great Orme is so great that scores of butterflies can be seen at once and this must count as one of the more spectacular sights for the lepidopterist in Britain.

* Ssp. argus, the heathland race, still occurs at South Stack, Anglesey but appears to have been lost elsewhere. A recent Butterfly Conservation survey on the Lleyn Peninsula failed to find the butterfly in any of its old sites.

* It has been suggested that the nationally important population at Hafod Garregog NNR represents the last surviving colony of a third subspecies, masseyi, which was described from northern England but is now extinct there. However, these butterflies are now thought to be of independent origin and are regarded as no more than a form. Regardless of their taxonomic status they represent the only surviving bog-dwelling population in Britain.

The habitat on the Great Orme’s Head appears to be kept in a favourable state by continuous light grazing but elsewhere some degree of disturbance may be needed to provide the necessary open vegetation structure with vigorously growing young plants. Burning and soil stripping are two possible management activities that can be used to ‘restart the succession’ but naturally it is important that only small areas are involved at one time.

There is only one brood per year with the flight season peaking in early July on the Great Orme and towards the end of July elsewhere. Various foodplants are used including Common Bird’s-foot Trefoil (Lotus corniculatus) and Common Rockrose (Helianthemum nummularium) on calcareous sites and heather species elsewhere. The butterfly is renowned for its dependence on certain species of ant, which provide essential care for the larvae and pupae.

Silver-studded Blues do look very similar to Common Blues and a close examination of the underside wing pattern may be needed to be sure of the identification. Apparently, the highly competent entomologists who surveyed Hafod Garregog in the 1970s completely overlooked the presence of the Silver-studded Blues, dismissing them as Common Blues. This story should be a lesson to the rest of us and it does suggest that, even now, there could still be unknown colonies in North Wales.