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Here comes some more questions...

Are these two hoverflies Crysotoxum species? Which species? How can I see the difference? (Becauce they are not "the same", are they?)

First fly:



Another picture at the first fly:




Second fly:

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Top one is C. elegans, lower one is festivum. You can see the difference in abdominal pattern, but there are related species to be aware of.
C. festivum has continuous black beading around the sides of the abdomen, and all yellow femora. The bars are also a characteristic shape.
C. elegans has yellow on the lateral margins of the abdomen, antennal segments 1 and 2 equal in length, and 3 equal to 1 and 2 together.
Hope this helps!

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It helps a lot! Thanks. I?m deeply impressed by your ability at this forum.

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Tony, are you sure the first one isn't C. arcuatum (=fasciatum)?

I do often find the lengths of antennal segments very difficult to judge correctly. The ratios apparently depend on gender and size of specimens and wind direction and, well, you get the idea.;) C. arcuatum and C. festivum and the two most common Chrysotoxum at latitude 60 in Scandinavia. But C. elegans has never been found on the Swedish mainland, the only records are from the ?land island where it is very rare and endangered!

Fauna Eur. lists elegans from Finland, but all specimens we have found in collections and checked belong other species (mainly C. arcuatum).

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Kahis is surely right about this not being elegans!
Also not C. arcuatum (=fasciatum) because that species is, in my opinion more rounded and a bit different in color pattern on the abdomen.
For me the species looks more like a female of Chrysotoxum cautum!
How about the distribution of that species in Northern Europe?
Greetings,

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Well, it wouldn't be the first time that a British key has failed to work on the mainland! But I don't think it is arcuatum. If it is, there's a serious problem with our understanding of antennal ratios in this genus! If I've made an error here (and it wouldn't be the first time! :D ) then I'd agree that it could be cautum. Time to go back to the collection for some more study!
Thanks for your comment, Amaira - as you can see, impressions can be misleading! ;)

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C. cautum is common on southern Sweden but idefinitely a rarity as far north as Stockholm.
amaira: Do you perhaps know Hans Bartch? He is writing a book on Swedish hoverflies. I bet he would like to take a look at photos of the cautum-candidate. I'll send his email address to you with an private message on this site if you don't have it.

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Kahis: I don?t know Hans Bartch yet, but I will :D and I have a contact through a contact - or how to say it. (sorry for my english) So I will send the pictures to him.

This is very exciting, and I follow your discussions with great interest! Learning and learning and learning (I hope at least ;) )
And I?m even more impressed!

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Hans B. have helped me before with photos of insects. I actually wrote him this summer with links to a few of my threads, but haven't got a reply. I suspect he is busy this time of year. Hopefully we can convince him to be a regular visitor on diptera.info* ;)

* ... or maybe he is already an anonymous guest B)

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I?m still impressed of your discussing, coming to the right answer.

Hans Bartsch tells it is a Chrysotoxum cautum. :D

C.cautum is rare here, but hot summers it sometimes appear in Stockholm too.


Is this too C. cautum? Seen three weeks later, 10 km away from the first one. It looks the same to me, but the pattern on abdomen is not quite alike. There is one more thin thread of yellow on this one.

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Hello Amaira,
Yes, this is without doubt also a female of Chrysotoxum cautum :D
The amount of yellow on the abdomen varies a little, especially at the hind border of the tergites.
greetings,

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Wonderful! Thanks Gerard!