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Unfortunately, I have not yet received any information regarding my enquiry about Thereva valida (https://diptera.i..._id=106959). But I suspect what the reason is - these Thereva females really are a mess. I encountered two more specimens in the same place, drinking in water-filled ruts on a forest path. One looked like T. nobilitata with its yellow-brown pubescence, also the halters (stalk brown, head whitish) matched. However, the shape of the frontal callus was not triangular-heart-shaped (as illustrated e.g. in http://soldierfli...20v1_1.pdf), but rather straight with a middle notch like in T. valida. The second specimen was less hairy and its colouration was more reminiscent of what I had already posted as a possible T. valida. In particular, the hairs on the head were not yellow, but white. The shape of the frontal callus corresponded to the yellow individual, but was slightly broader than that of the presumed T. valida. However, the halters should be darker in T. valida. In pictures from reliable sources like https://www.flick...893639875/ this varies quite a bit.
I have the feeling that all three could belong to the same species - based on the callus shape, this would be T. valida. The bristles on the underside of the hind legs were not clearly visible in the photos. So if anyone has more experience with variability in hair colouration and callus shape, I would be grateful for any information.
Thanks in advance, Sundew

Here is the yellow one.