Alcetas is very similar to Short-tailed Blue (E. argiades), usually slightly smaller, but principally differentiated by the unh marginal lunule(s) (s1c and s2) adjacent to the tail: in argiades the lunules are orange-filled whereas in alcetas there is no trace of orange (maybe only a few orange scales). There is virtually no difference in the undersides of the sexes of alcetas. The male alcetas tends to have thinner black borders to the blue on the upperside, as compared to argiades, and the argiades male uph sometimes has black marginal spots. The female alcetas upperside is entirely black with no trace of blue scales, and otherwise unmarked, probably the darkest butterfly upperside; the female argiades usually has areas of blue scales in the basal region and an orange spot at the uph anal angle. The argiades tails are usually slightly longer than those of alcetas. The alcetas tails can sometimes be so small that only the "bump" in the marginal line indicates their existence.

Alcetas is a butterfly of southern France, quite localised in Provence, where I have only ever seen it in in singles in two locations. In 2010 I saw 22437 in the Hautes-Alpes in a location where it is not supposed to exist according to the distribution atlas. It seems more common (or less uncommon) in the northern parts of its range, and I have seen it near Lyon and in the Dordogne where on occasions it has been common in certain locations, although the numbers seem to vary year on year.

In the new European taxonomy, this species now has the scientific name Cupido alcetas.

observations

a typical male although the black borders are rather thicker than normal. This photo shows the blue colour as rather paler than would be expected, perhaps a camera effect.

a female, with constant black-brown colouration.

a female, slightly fresher than 9143, almost black with no loss of scales as yet.

a beautiful very pale ground colour and quite strong marginal marks. The unh marginal lunule in s1c has, untypically, a few orange scales, only visible in close-up.

a female, only known for certain because it was seen in flight.