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There is also a key here:
https://rua.ua.es/dspace/bitstream/10045/77172/5/2018_Nedeljkovic_etal_CanEntomol_revised.pdf

The latest version of the Syrph the Net key that I could find is this one:
https://pollinators.ie/wordpress/wp-content/uploads/2018/05/StN-2017-KEYS-to-SPECIES.pdf

I am convinced that we also have X. dives in Denmark, but that it has been misidentified as X. stackelbergi. I identified all my specimens using the Dutch and the StN keys. The result: 7 X. dives, 9 X. pedissequum, 0 X stackelbergi.

But I may be wrong, off course.;)