Silver Studded Blue (Plebejus argus)
A small butterfly, it is smaller than a Common Blue with much brighter markings on the under side of its wings. It is quite distinctive in habitat, however, as a heathland butterfly
and can be found from late June until early August on the heathland of Purbeck, notably at Arne. It also occurs on grass downland and can be found on Portland too.
Being a heath specialist, it is not surprising that it's favoured food plants are Gorse and Broom and the larvae also feed on heather and Bird's-foot Trefoil.
Blue butterflies are in general lovely insects and the Silver Studded Blue is certainly one of the best.