I have great difficulty with the huge variety of forms of
athalia and
diamina. In the Swiss Alps it is easy, but in the Pyrenees, for example, with form
vernetensis flying, I'm not sure I've really mastered it (the underside of
vernetensis is quite unlike that of the nominate form). That said, I think I agree with you that yours is probably
athalia - a rather dark male.
I would rule out
golgus, incidentally, for your female blue, because the underside is clearly not
Plebicula (the white submarginal area on the forewing is obvious in
Plebicula species). It is true that
thersites females usually have some blue on, but this is more true for the first generation. Did you notice the flowers?
Thersites is always found in close proximity to sainfoin - I have never known an exception to this rule.
Border width can be dodgy with
idas/
argus. I have a theory which seems to hold in the vast, vast majority of cases, but hasn't yet been patented. On the hindwing, there is a fork enclosing space 6 (I think it is space 6). In
argus, the area above this is solid dark and the dark extends into the fork, at least in the form of scattered dark scaling obscuring it a little. In
idas the fork is completely clear of dark scaling and the area above it usually shows at least some clear blue, basally. In the picture below, the upper is
idas, the lower
argus, both taken this year. The red lines indicate the area I mean:
Your butterfly has the dark leading edge of
argus, and dark scaling within the fork, as well as the broad margins, which in this case are sufficient alone. But I have found my theory to be useful in many difficult cases.
Guy
