The male has brilliant upperwings of almost turquoise blue, and outer margins edged with a fine black line. The female upperwings are mainly chocolate-brown, but often dusted near the base with turquoise-blue, and have small black eyespots within orange and blue surrounds along the lower margins. Dark veins cross the white fringes in both sexes, just entering the body of the wings. The underwings are spotted with orange near the edges.

Many female Adonis and Chalkhill Blues are identical, except on the undersides where the pupil between eyespot and wing edge is blue on this species but white on the Chalkhill blue. The Common blue has no dark veins across its white fringes in either sex.

Dimensions:
Adult wingspan: 30-40mm.

National:
As with the Chalkhill Blue, this butterfly is restricted to the calcareous grasslands of southern England.

At Durlston:
The numbers on the Park have been relatively low with none seen in some years. However, there was a dramatic increase in numbers from 1997. The reason for this is unknown. It is now common on Round Down and around the Gully area.

It lays its eggs only on Horseshoe Vetch and then usually on the smallest plants close to the ground which provide the optimum micro-climate for the larvae. Throughout its development it is attended to by ants. The larvae of the second generation overwinter and pupate in the spring where they may be buried or taken into ant nests. The adult is active from mid May to early June with the second generation active from early August to late September.