This, our smallest butterfly, is easy to identify. The tiny upperwings have no pattern: females are dark brown, males smokey-black with a dusting of silvery-blue scales near the body. The fringes are clear white with no veining. The underwings are very distinctive: silver-grey with a scattering of tiny black dots and none of the orange markings found on other blues.

Although unmistakable at rest, its silvery wings resemble the Brown Argus during flight.

Dimensions:
Adult wingspan: 18-27mm.

National:
This species occurs very locally and predominantly upon chalk and limestone grasslands throughout much of southern England but occurs sporadically elsewhere in Britain. The population is declining.

At Durlston:
This butterfly is restricted to Round Down, the Gully area and grassland areas adjacent to the coast. In the Round Down area, numbers have fluctuated greatly. Numbers were low in the east sector but have slowly increased since the mid-1990’s. Two colonies are present in fields 7 and 9 and fields 14 and 17 and it is apparent that the species has been expanding in the last ten years.

The larval foodplant is Kidney Vetch Anthyllis vulneraria. The butterfly is generally single brooded and is on the wing from mid May (occasionally early April) to mid July with a second brood occurring from late July to early September. The adult lays a single egg within the flower heads of the vetch. The larvae, when fully grown, descend and overwinter in the soil until the following spring when they pupate, except second broods that presumably pupate immediately. Under normal conditions, the butterfly is seemingly sedentary and thus forms distinct colonies. However, adults may move greater distances under certain conditions, e.g., hot weather, over-population, etc.