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Thick-headed Fly - Physocephala marginata - female

Thick-headed Fly - Physocephala marginata - Female
South Hampton School, City of Richmond County, Virginia, USA
July 15, 2012

Images of this individual: tag all
Thick-headed Fly - Physocephala marginata - female Thick-headed Fly - Physocephala marginata - female

Moved from Physocephala furcillata.

See comment below.

Beatriz, this is funny...
...because I've learned much of the following by reading, cross-referencing, and reflecting on Lee's comments on various Conopinae posts, and didn't recognize and appreciate many of these points until prompted by his observations. But I too have known things and written them down, only to later forget and err. (In fact, I'm writing all this down as a reference, partly in case I forget, and err in the future! :-) Also, I'm grateful when someone corrects me, so here goes...

While both P. furcillata and P. marginata have hyaline discal cells, I'm nearly certain the conopid in this post is P. marginata for the following reasons:

1) the yellowish-white dusted humeral dashes here (Lee calls them "shoulder pads") are fairly large (in furcillata they're typically short and inset from the lateral edge of the dorsum...or entirely absent);

2) the scutellum is red here (in furcillata it's typically very dark...basically appearing black);

3) the costal cell here (i.e. thin sliver-like cell along leading edge of wing) has the same dark color as the marginal cells beyond it. In furcillata at least the distal portion of the costal cell (i.e. the "2nd" costal) is typically a lighter brown;

4) the pollinose markings on the pleura here (between the middle leg and the wing base) conform to those characteristic of P. marginata (i.e. a lower triangular area with a narrower linear extension approaching the wing base...see this curated image);

5) the 1st segment of the antenna here is not particularly short (in furcillata it is...see couplet 3 in Williston's key here);

6) the range of furcillata is generally northern (i.e. from Pennsylvania northeast to Nova Scotia and west to Alberta), whereas this post is from Virginia, which lies in the more southerly range of marginata (i.e. New Hampshire south to Florida, and west to British Columbia).

Also worth mentioning for reference, though not visible in these two images, are two other significant characters separating marginata and furcillata, which appear in Williston's 1883 key above as well as Camras' 1996 key here and numerous species descriptions. They are:

7) cheeks dark on edges with pale central area in marginata vs. cheeks uniformly black in furcillata; and

8) facial grooves dark in marginata vs. facial grooves pale in furcillata.

Note that the facial grooves lie within the area bounded by the facial ridges, the latter forming an "inverted V" shape between the base of the antennae and the mouthparts. And in many images, care must be taken to avoid confusing possible dark facial grooves with the black linear extensions of the medial line of the frons, which forks at the base of the antennae and runs a short ways along the outer edges of the facial ridges. The two characters 7) and 8) above are illustrated in the posts below for P. marginata and P. furcillata, respectively:

By the way, most of the remarks above apply to the posts currently placed under P. furcillata below:

They are all P. marginata. I'll move those posts soon and refer to the comments here as an explanation.

I was concerned about these after I moved them following Lee's determinations and was thinking of moving them back to a higher taxonomic level. Glad you took care of them.

Thanks for sharing such detailed information. This makes a great guide. I see you added this to the species page.

Your welcome,'s a pleasure :-)
I've been studying this genus (and family) on-and-off now for well over a year: reading references; correcting my often erroneous initial mis-interpretations of tricky nuances; slowly accumulating knowledge; and spending lots of time refining my understanding of the group. At last things are cooking down to where I can integrate them into some sort of comprehensible unity that's consistent and that I can grasp. So I figure sharing what I've learned, and helping others who are interested in learning about it too, is one of the best things I can do with it all. It's pretty satisfying...I love entomology! And BugGuide :-)

Moved from Physocephala.

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