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Hello Jorg,

xylota: hind tibia is said to have 20% of the base yellowish-white. the species in your photo has a black base.
chalcosyrphus: abdomen has four large and rectangular yellow or gray spots versus smaller yellow spots of abiens.
I lean towards Chalcosyrphus nemorum but you would have to ask a Syrphidae specialist since i would require a specimen or a view of genitalia.

Best wishes,
John

Hi Jörg

I cannot get to my foto drive at the moment, i have to get my son to school. I will post some photos here later today and also send to you an email message

Best wishes,
John

Hi Jörg,

I have photos of Chalcosyrphus nemorum male and a comparison photo of Xylota segnis female. Your photo contains a female Chalcosyrphus nemorum - the only other Chalcosyrphus recorded in Germany, to my knowledge, is chalcosyrphus femoratus and the femora are reddish orange.

note the pale base of the hind tibiae on Xylota spp.

edit: there are 3 other Chalcosyrphus recorded in Germany besides femoratus and none of them are candidates. I do not see a need for a confer. Also, the hind femora of Chalcosyrphus are swollen compared to Xylota.

Best wishes,
John

Hallo Jörg,

The hind femur and the overall appearance is a determining factor for me whenever i am in the field. The size of the spots on the abdomen are also a factor. I find it difficult to describe but there is a visual difference between the two species and i deduce it to be stoutness of body and the hind femur. Bristles on the hind femur are also different. I can see larger bristles in your photo which are smaller on X. abiens. The best photographic angle of these flies is lateral so that the hind femur is clearly visible. However, one can see the swollen hind femur even when viewed from above but that takes practice to recognize. In my experience, the fly is a better match with Chalcosyrphus. Despite the fact that abiens may also have a dark base on the hind tibia. I have to investigate abiens a bit more on my own. I need to view several males and females under a microscope.

I do not focus on Syrphidae but i do have documents with keys, descriptions and drawings of genitalia. I will try to learn more about Syrphidae but i specialize in Calliphoridae and Pollenidae. I also study Helina and Phaonia of Muscidae. I like Fanniidae because of the forensically important relationship with Calliphoridae. Pollenia flies are my favorites! Most important is the fact that i am technically just a man that likes to study flies and spiders. I am certainly not an expert and i do not have a degree in Biology.

Best wishes,
John