Identification, Images, & Information
For Insects, Spiders & Their Kin
For the United States & Canada
Home
» Guide »
Arthropods (Arthropoda)
»
Hexapods (Hexapoda)
»
Insects (Insecta)
»
Flies (Diptera)
»
"Acalyptratae"
»
Sciomyzoidea
»
Thick-headed Flies (Conopidae)
»
Conopinae
»
Physocephala
»
Physocephala marginata
Photo#674509
Copyright © 2012
James Shelton
Thick-headed Fly -
Physocephala marginata
-
South Hampton School, City of Richmond County, Virginia, USA
July 15, 2012
Images of this individual:
tag all
Contributed by
James Shelton
on 15 July, 2012 - 5:42pm
Last updated 28 June, 2018 - 7:17pm
Moved
Moved from
Physocephala furcillata
.
See comment below.
…
Aaron Schusteff
, 28 December, 2013 - 12:05am
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.
…
Aaron Schusteff
, 28 December, 2013 - 12:01am
Thanks
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.
…
Beatriz Moisset
, 28 December, 2013 - 7:02am
Thanks.
Thanks for sharing such detailed information. This makes a great guide. I see you added this to the species page.
…
James Shelton
, 28 December, 2013 - 12:34am
Your welcome, James...it'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 :-)
…
Aaron Schusteff
, 28 December, 2013 - 12:55am
Moved
Moved from
Physocephala
.
…
Beatriz Moisset
, 11 December, 2013 - 7:32pm