This is one of a family of very similar hairstreaks of the Satyrium family, including Ilex (S. ilicis), False Ilex (S. esculi), White-letter (S. w-album), Black (S. pruni) and the less-similar Blue-spot (S. pruni). Acaciae has larger and rounder red spots on the unh with internal black triangles on the margin and black edging externally. The post-discal white line is also (usually) quite strong and almost straight (c.f. ilicis and w-album). Although it looks superficially similar to the other Satyrium species, with a clear view it can be identified with some confidence.

Prior to 2004 I had only seen it in one locality in the Alpes-Maritimes. In 2004 I saw it in several different localities, all at an altitude of 1000m+, but never more than one individual in any locality. In 2006 I found it in large numbers in Var from late May to late June with a peak emergence around the second week in June when it was out in good numbers, flying in company with both ilicis, esculi, and spini.

The low-lying yellow flowers of the Helichrysum family seemed to be a strongly favoured nectar source of all the Satyrium species, often with several hairstreaks on each flowerhead. I revisited the same site in subsequent years and the Satyrium hairstreaks could be counted in hundreds.

The sexes are similar, but it appears that the female has a more prominent post-discal line, stronger lunules and markings and slightly longer tails. The tip of the female abdomen is black (just about visible in 6799 below).

observations

a male, for the same reasons as 10743.

a male, I suspect, based on the tip of the abdomen is just visible and does not appear to be black. 

a female, based on the strong black-edged white discal line extending the entire length of both wings, and the just-visible black tip at the end of the abdomen.