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Photo#103438
Unknown Insect In Pasqueflower - Lapposyrphus lapponicus

Unknown Insect In Pasqueflower - Lapposyrphus lapponicus
Near Fort Collins, Larimer County, Colorado, USA
April 14, 2007
Size: 1/2 inch
I have no idea what this is. It looks like something is on its back.

Moved
Moved from Eupeodes.

Moved
Moved from Scaeva selenitica.

Scaeva pyrastri
Cumuseum doesnt list Scaeva selenitica. It is an Eastern species and European species.

Cumuseum lists only

Genus Scaeva
Scaeva melanostoma (Macquart 1842)
Scaeva pyrastri (Linnaeus 1758)

Cockerell wrote: Scaeva Fabricius. 8. pyrastri Linne*; University Campus, November (C.).,Boulder CO.

 
S pyrastri is wide spread all
S pyrastri is wide spread all over the US, melanostoma is a Neotropical species and selenitica is European, but it might have been introduced to the US, but I have never seen a specimen and the one in the picture is very close to selenitica.

Moved
Moved from Syrphini.

Looks very much like a female
Looks very much like a female of the introduced Scaeva selenitica. In contrast, S. pyrastri has white bands while selenitica has yellow one's...

 
Scaeva pyrastri
has YELLOW (female) and white (male) bands according to
wikipwedia ,
see also Joachim & Hiroko Haupt: Fliegen und Muecken, 1998, page 202,
which shows yellow bands for S. pyrastri (color photo).
check also here

 
Sorry but the wiki site only
Sorry but the wiki site only mentions that the females sometimes have a completely black abdomen and it only refers to the spots as "hell" meaning light, without a reference to the color. The picture in Haupts book is indeed yellow, but this is a male (so it would contradict your statement about the wiki page) and the authors are not the best experts in the field.
The more important character is the shape of the "half moon" spots. In selenitica the beginning and the end of the spots on tergite 3 &4 are in equal distance from the front margin of the tergite, while in pyrastri the inner end of the spots is closer to the front margin of the tergite, which is very well visible in the picture in the link Ron provided. Also pyrastri is more robust the marks are white and thicker, while selenitica has thinner yellowish marks on the abdomen.
But in general Scaeva is not that easy of a genus (although there are not too many species) and before I give a definite identification as selenetica, I would like to have a specimen on hand. There is also the outside chance that the fly here in the picture might be a different genus - unlikely but possible.

 
I just showed the pic to Chri
I just showed the pic to Chris Thompson, and he said that this is a Eupeodes! And selenitica was only found in NC and very likely did not establish successfully...

 
Dueling Photos
Wikipedia looks white to me. Photo in J&H has a strong color cast. See here: http://perdidoenelamazonas.blogspot.com/2009_02_01_archive.html

 
Thanks, Martin.
That clears things up. I'll scurry to my files and see if I have any S. selenitica.

Moved
Moved from Syrphid Flies.

Scaeva pyrastri, most likely
I've shot several, but the markings were more white than yours. That seems to hold true on other posts, but I'd guess it's a variation. Let's hope an expert weighs in on this.

If memory serves, the markings are distinct and different than other syrphids. (That often isn't the case with syrphids, as Joe pointed out.)

 
Distinct and different...
from this specimen :)

See the comments on this image:

 
Missing link for "Distilnct and different..."?
Chuck, can you reconstruct?

 
'Fraid not...
My gray matter has faded a little after being through the wash a few times...

At any rate, your thumbnail has apparently since transformed from a Scaeva to a Eupeodes, rendering my comments moot.

 
Thanks for responding.
This one and its offspring have gotten messy. (Peter Bryant calls such identity changers "imposters". I tend to agree.)

 
There are three pairs of light "bands" on each
On Eupeodes, the pair nearest the thorax doesn't touch, while the others do. On Scaeva, none of the pairs touch. Also, the shapes of the bands differ, with those of Scaeva being more curved. I continue to call their appearance distinct and different.

Eupeodes and Syrphus are the look-alikes.

Flower Fly
Looks to me like a fly in the family Syrphidae. They're a large family that tend to mimic bees and wasps, often visiting flowers for nectar. Some feed on decaying organic matter as larvae, while others eat aphids and other small pests.

As for which species, I'm not nearly knowledgable enough to even guess.

 
Thanks, Chuck!
It looks to me like that's the correct family, so I'll move it there. I'm still curious what the thing on its back is.

 
Probably part of its back...
They have the thorax (the middle of the three main body sections) subdivided into smaller structures, with a technical term for each which I've forgotten. This particular structure is bigger in proportion to the others than I've seen, but it looks to be normal otherwise. We have some real fly experts here who'll be able to give much much more detail than my vague half-rememberings

 
I suppose the structure being
I suppose the structure being alluded to is the scutellum... a structure worth remembering, as it is used heavily for IDing flies, beetles and true bugs.... as per this fly: all I can say is that it's in the tribe Syrphini... there are about a half dozen genera that all look more-or-less like this (which I take to mean that this group has been studied by 'splitters')... Gerard can probably ID it

 
I think I was thinking...
of the mesoscutellum as opposed to the postscutellum, but looking further I see that the mesoscutellum is usually refered to simply as the scutellum. Probably best for me to leave explanations of fly anatomy to dipterists...

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