The large males are unmistakable both in flight and when basking, due to their cold, pale, silvery-blue upperwings. The underwings are also distinctive - heavily spotted on a light grey background that appears almost white in the sun.

The females have chocolate-brown upperwings, tinged to a variable extent by silver-blue near the body. Elderly females overlap with the first Adonis Blues in late August and early September.

They differ from female Adonis Blues in having white rather than blue outer circles to the eye spots along the bottom edges of the upper hindwings, and from all other Blues in having brown vein ends across the white fringes, making the edges look chequered.

Dimensions:
Adult wingspan: 33-40mm.

National:
This blue is restricted to the chalk and limestone downlands of southern England.

At Durlston:
It appears to be restricted to Round Down and the Gully but is not uncommon, with a few wanderers appearing in the east sector. It would be useful to identify the location and extent of the colonies on Round Down particularly as there has been a decline. It is now found predominantly at the top of The Gully.

As the butterfly overwinters in the egg stage, the eggs are not always laid directly on the plant. In the spring the larvae hatch and are attended by ants. This attraction remains into the pupal stage where the ants take them into their nests or bury them. The adults emerge from early July and remain active to mid-September.