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Thanks chaps, you really are being very helpful as usual.
Possibly by way of reward, Pieter has presented another useful image, showing the antennae in better detail as Theo requested. I attach it.
Incidentally it also shows the proboscis from a more helpful angle, consistently with Steve's remarks.
John, thanks, and your description of the eyes of the male Chrysops of course matches the full-face image very well.