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The photographer, Espen Tangen Aarnes of the BioForsk research station in Pasvik, Finnmark, came back from fieldwork. He agreed to post the picture here.

I also received feedback from Trevor Williams, the most prolific iridiovirus expert. He said that an iridivuris infection is an unlikely explanation, basically because blue adult diptera have not been reported before.

Yet I haven't found a more plausible explanation for the colour.

I think the species depicted is T. (Beringotipula) unca.

Does anyone know of diptera that occur naturally in this colour