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St Marks Fly Bibio sp

Hwe present you with a number of unidentified St Mark's Flies. We can not put a name on them with some certainty. At least three species have to be taken into consideration: Bibio marci, Bibio hortulanus and Bibio johannis. The females can easily be told apart, actually. The females of Bibio marci are entirely black and do not have a black spot in the wings. The females of Bibio hortulanis have a red thorax. The females of Bibio johannis are entirely black, but also have a black dot in the wings. So one may conclude the fames in these pictures are all Bibio marci. And they most probably are. But there are a few other species just like it, so we can't be sure, alas. The males are very hard to tell apart, for all three species have black males with no dot in the wings. So to be on the sure side of it, we call all of these: Bibio sp, or St Mark's Flies.