I just compared to other images on the Guide like this one...

I think most of the flies that look like yours are T. pennipes but nobody seems to know for sure. There are six American species in the genus, four of them found in the East. One or two have more black on the abdomen than your fly and one of those has more clear on the wings also. So there might be one, two, or three species that look like this. I know of no published key.

how old they are, and if they're ever updated. Of the six species listed here, only three are represented as images on the internet, and all are from Bug Guide. While it may simply be ignorance on my part, I question the value of such lists.

Hi Ron,
I just wanted to say (although I'm not sure what you mean by "species list") but in terms of species determination and delineation, there are professional scientists that work with issues of taxonomy. I took my first taxonomy (faunistics) class with a renowned entomologist/taxonomist - he revolutionized the taxonomy of several entire groups of insects. See his webpage at: http://insects.ummz.lsa.umich.edu/~ethanbr/chiro/Books-Bibs/saethref.html --- many scientists such as him work in the lab & field, and publish findings in intl. sci journals, and their resulting Identification Keys (based on their studies) are constantly being updated as OTHER scientists contribute new findings in new publications. It might take a while for new findings to be incorporated in the "newfangled" online observation-sharing sites.

I was referring to the Bug Guide Info page for this genus http://bugguide.net/node/view/2798, most specifically to the Numbers heading. In this case, we have just a quantity (6) for species.

Often with flies - particularly syrphids - there are many more species, and they're listed by individual names. Trying to find more info on many of these flies on-line turns up nothing, and I often wonder if the lists are overly expansive.

Example: For Eristalis, we have images of just seven species on display here. Nearctica and Arnett list 23 species, while ITIS lists 27 species. With as many people as we have shooting syrphids, I question whether we've missed so many species. And I note that the experts don't agree amongst themselves as to the number of species. I'd guess there really aren't clear-cut answers to questions like mine.

In my opinion, biodiversity surveys and the participation by observers/the public are becoming very important. The power of this tool far outstrips the speed at which the researchers can go out and "collect" data. But the observations on this site will be useful only if the data can become sortable - and as you say, if ID's are being made based on the list only on this site, well that (seems to me) can create a mess. If there are too few species listed, then wouldn't it be best just to relegate the species to genus, until the list on this site at least somewhat more complete as per one of the official sources? That way some expert can sort out all of it at some later date? I am creating a biodiversity database for the Shelby Forest where I live (I'd like it to contribute to its conservation), and so questions like this are important in terms of actually measuring the biodiversity based on species #.

what you mean. However, I have not seen a page that lists all the species found within a genus, so that is one way of seeing those, and perhaps some images (at least). I'm new to the site (started last month), so I have not learned everything about it yet - by a long shot!]
thanks, though.

I've been edging out of the site for a couple years, after being a major contributor. Memory doesn't serve well on which syrphids were "overrepresented" wrt species. I think Copestylum might be a good example, but am too lazy and disconnected to look more deeply into this.

I just added unknown Copestylum image today :) Please look deeply, Ron ;) lol

I noticed there are some imges looks little different. So, I understand your dilemma (?).
Do you think I shouldn't add this image as T.pennipes? Just go Trichopoda to be safe?

Anyway, thanks for the information, John!