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Hi,
I found this Chalcosyrphus sp. on a dead Aspen in the end of May in Saxony (Germany). Ten days earlier I photographed at the same place a male Chalcosyrphus femoratus. Are the hind tibiae enough bended for a female Chalosyrphus femoratus? Halteres seem to be dark yellow on the first picture. Do you agree with C. femoratus or is it a C. valgus?
Greetings
Marion

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2nd picture

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It is difficult to say, we need to see the ventral tip of the hind tibia. I add a character comparison of Chalcosyrphus from my Syrphidae paper of last October (I could send you a PDF if you are interested). In my two gallery pictures of C. femoratus, especially in https://diptera.i...to_id=8785, you can see the very light halter knob and the orange basoflagellomeres. Your fly is a bit too dark for C. femoratus, I am afraid...
Regards, Sundew

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Hi Sundew,
thank you very much for the detailed answer. Your paper is very welcome and would be helpful for me. I have only the old book with the key of Gerald Bothe where the flies are hidden under names which were valid 38 years ago.
I will look again to all picture of that fly.
Best regards, Marion

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Difficult. I attach 2 more pictures.
Unfortunately the tip of the hind tibiae is not visible in any picture. The arista seems to be a little lighter than the pedicellus and basoflagellomer and at least the left wing stigma looks light or yellow-brown. Now I think the probability is higher that it is an Chalcosyrphus valgus. If you agree I will store it as Chalcosyrphus cf. valgus.

Greetings, Marion

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another picture

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To confirm this ID, consider that Ch. valgus should have a long 4th tergite, the abdomen should look longer than in other Chalcosyrphus species, or the species should look slimmer, respectively. Stigma should be quite pale.

Sometimes it is difficult, I have pictures of all these species, but sometimes I am not able to identify a new one.

Regards, Matej

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Interesting - differences in tergite length are not mentioned in the keys I know.
Here is a nice picture of a C. femoratus female: https://www.galer..._rouge.jpg. The pale haltere knob is striking, and the arista that is darker than the orange basoflagellomere is well seen. Also the large, triangular flange at the apex of the hind tibia is visible.
I consider your female C. valgus.
Best wishes, Sundew
PS. Did you get my Syrphidae paper that I sent you via e-mail?

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Thank you very much for ID.
It's nice to find 2 Chalcosyrphus species on the same aspen.

Best wishes, Marion

PS: Thanks, I received the Syrphidae paper and answered.