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Two males Neoitamus socius?

Location: Nestos river, Northern Greece
Alt.: <100m
Date: 01-07-2017

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The look like Machimus species but admittedly the genitalia seem to be weird, probably due to the angle.... more pictures?

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Yes, it is either the angle or another male trying to get hold of the prey.
If the lower one is a female then apparently it is a species where the male is approx. the same size. And they mate in a head to head position. But that leaves too many possible candidates I guess.
Unfortunately this is my only picture. I’ll keep it as an uncertain Machimus. Thanks for your reply.
Regards,
David

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It is a copula, the upper creature is the male grabbing the ovipositor, but because of the angle we can't see the shape of the genitalia. Well, we can reduce the possibilities by the fact that the legs are entirely black and there is also visible a small tab at the margin of the eighth sternite, Could you give a reliable size? We will never know the species unless you collected the specimens.

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Hi Reinoud,
In general, using the focal distance data in the EXIF-file it is possible to do a recalculation of the image width and height of the original uncropped photo. Because in this case the flies seem to be positioned more or less parallel to the image-plane, this would allow a reliable estimation of their size.
Unfortunately, the focal distance value that my Pentax camera stores in its exif-file does not represent the exact distance but a relatively wide distance range. Taking this into account, the size of the male fly (measured without antennas) can be calculated to be between 17mm and 28mm. This will only rule out some of the smallest species.

In my opinion collecting specimens for scientific purposes is justifiable, but collecting them out of personal curiosity for their id is not.
Best regards,
David

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Hello David,
Comparing the specimens to the prey, which seems to be a Vespula species, i think we can safely assume that these robberflies are pretty big, over 20 mm. The genus Machimus is in dire need of a revision, it is a taxonomic nightmare :-). Besides that there is still a lot unknown about the Asilidae of southern Europe. In this case all we can say is that these specimens belong to the group of large Machimus species with black legs.

Of course collecting serves no purpose if not for research or to share with a community. Besides that, collecting is prohibited in most countries. But remember, all science starts with curiosity and an average car kills way more insects than a fanatic entomologist. Billions and billions of insects are killed by traffic, construction activity, agriculture, pesticides etc, etc etc. In short, the discussion about collecting is a difficult one.