The Brown Argus is is one of the so-called 'blues' that has no blue scales on its upperwings. Males and females are quite similar in appearance but females are nearer the upper end of the 2.5 to 3.1cm wingspan range, males being smaller.
The specimen shown here is Aricia agestis f. cramera and was photographed in the Algarve region of Portugal. (Picture: Rob Petley-Jones)
In Britain the Brown Argus is mainly concentrated in the chalk downland areas of central and eastern England, with scattered populations along the calcium-rich sand dune areas of coastal Wales but none in Ireland. Further north this species is replaced by the Northern Brown Argus, Aricia artaxerxes.
Elsewhere the Brown Argus can be found locally throughout most of Europe except Scandinavia. To the south its range extends into northern Africa and to the east this butterfly also occurs in parts of the Middle East and Asia.
In northern and central Europe there are two overlapping generations of the Brown Argus; they emerge in May and in August, with the males preceding the females by a few days. On the Iberian peninsula and in Mediterranean countries there are normally three broods, the adults appearing in April, July and finally October.
The main larval foodplant is Common Rock-rose (Helianthemum nummularium), although some members of the plant family Geraniaceae are also used occasionally. The pale eggs, laid on the undersides of leaves of the larval foodplant, hatch in about a week; then the tiny larvae eat the underside of the leaves so that just the upper cuticle rtemains in the form of shiny translucent patches.
As the caterpillars from the first generation develop, they are tended by ants that take honey dew from them. In Britain, when fully grown these green caterpillars with purplish stripes pupate on the ground in July, and their chrysalises are buried by ants. A week or so later the winged adults emerge.
Second generation eggs hatch in August, and the caterpillars feed for a short time and then go into hibernation right through the winter until March of the following year; then they resume feeding before by the end of March.