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Species ID help - Polybiomyia townsendi - male

Species ID help - Polybiomyia townsendi - Male
Albuquerque, Bernalillo County, New Mexico, USA
May 9, 2014
Size: ~12mm
Backyard on a yucca plant leaf. Image is a little blurry hope a species ID is possible, frass if image is not up to par.

Moved from Polybiomyia.

Mystery least to genus
Moved from Conopinae.

Mark sent me a set of photos for a similar specimen that had enough detail to key. It went unequivocally to family Syrphidae in the MND I(1), and to either genus Polybiomyia or Sphiximorpha in the key to syrphid genera in MND II(2). The (somewhat obscure) character separating those two genera was not visible in any of Mark's photos...but studying the images of both species on BugGuide and the online Key to Nearctic Syrphidae (see here and here) made it clear this was the former.

In fact, it seems very likely this is Polybiomyia townsendi...from a comparison with the post below (also from New Mexico):

But until I can get a hold of a copy of the reference below:

  Shannon, R.C. 1925. The Syrphid-flies of the subfamily Ceriodinae in the U.S. National Museum collection. Insecutor Inscitiae Menstruus. 13: 48-65. try to verify species...I figure it's best to move this image to genus. (Perhaps Martin or someone else knowledgeable with this genus, or in possesion of the above reference, will see this post and be able to appropriately place it to species...else I'll try to get a copy of Shannon (1925) next time I visit a good library.)

Polybiomyia townsendi
I have a copy of the above paper.

This specimen keys out to [i]Polybiomyia townsendi{/i]

It lacks prescutellar spots. It has prescullar stripes. It lacks a yellow pteropleura. This leaves only the above species.

Your the man,
Thanks again for all your work!

Yea!! I found one in CA! :-)
See post below:


By the way, the holoptic eyes of your post here indicate a male (as opposed to dichoptic-eyed female in my post).

Bizarre...very anomalous for Conopinae!!
I agree that, in overall gestalt, this fly looks like a member of Conopinae (and I'd think genus Physoconops)...but if so it is highly aberrant! Below are a number of peculiarities of this individual...assuming it is indeed in the subfamily Conopinae of Conopidae:

1) First off, the eyes of this fly appear to be touching along much of the vertex, except for a the tiny ocellar tubercle at the hind edge of the vertex. Of course male flies of many dipteran taxa have the upper edges of their eyes touching. However I believe this is not the case for any (non-aberrant) members of the subfamily far as I know both females and males there have eyes well separated, at least in the nearctic species.

2) Though the photo in this post isn't as clear as you or I would like, one can still discern from the full-size version that the wing venation is quite abnormal for either of the nearctic genera of Conopinae. Compare the left wing in the photo with the typical venation shown for Physocephala and Physoconops, respectively, in the diagrams below (click on the diagrams to get larger images, complete with explanations of wing vein and cell terms):


In the full-size version of the photo it appears that the normally short basal medial cell (labelled "bm" in the reference diagram at left) is distorted into an extremely elongate form, and the basal radial cell ("br" in the diagram) is also abnormally elongate. The short black cross-vein in the darkest central part of the left wing infuscation looks like the vestige of what would normally be cross-vein "r-m"...except that it's more obliquely angled than usual and (more significantly) its posterior end meets the medial vein well before the tip of the basal radial cell, rather than midway along the discal cell ("dm"). That's very strange!! Usually cross-vein r-m forms the distal edge of cell br...separating it from the 1st posterior cell, of which it forms the proximal edge. The discal cell here is consequently very distorted...very much shortened and squeezed out towards the distal end of the wing.

3) Another unusual aspect of this fly is the color of its's entirely pale-yellow (almost white, but the conopid literature often refers to such almost-white areas as "yellow", and vice-versa). The scutellum in Conopinae is usually dark (i.e. red, brown, or black...or sometimes partly yellow...but I've never seen one with that large a patch of yellow!)

4) If this were in Physoconops (which would be my impression, assuming it's indeed in Conopinae), another anomaly would be the fairly light color of the tarsi. In Physoconops every individual I've scrutinized has all the tarsi a dark contrast to many Physocephala, which have at least the upper tarsi yellowish to dark red, but relatively light compared to Physoconops.

Maybe we're erring in thinking this is in Conopidae? If it is, I'd think it would indeed have to be in the subfamily Conopinae, and from the antennal proportions; uniform width of the hind tibiae; and wing infuscation...I'd think in would be in genus Physoconops. Beyond that, from the well-defined lateral (pale) yellow stripes on the dorsum of the thorax; overall rufous coloration; and what appears to be the semblance of a "complete post-vertical pollinose stripe" best shot at species would be Physoconops townsendi. That species, along with P. fronto, P. gracilis, P. brachyrhynchus and P. discalis are the species of Physoconops recorded from New Mexico in the literature. P. brachyrhynchus and P. discalis are dark species overall, and I'd think they can be eliminated.

At any rate, as this was found in your yard, perhaps you'll get a future opportunity to take photos of another (perhaps less anomalous) one?! :-) Ideally, you'd want to get clear images of wing venation, together with dorsal and profiles shot for overall color pattern of the body...AND...frontal and profile views of the head (in particular, showing the color of the facial grooves under the antennae and above the mouthparts, and the "cheeks" under the eye).

If it's indeed in Physoconops, it's one that is underrepresented on BugGuide...and a set of clear, diagnostic images would be a wonderful and useful addition to BugGuide!

If it's a conopid...then it's definitely an aberrant Physoconops
I just checked the Conopidae treatment in the MND(1) and it states right near the beginning that all members of the family have: "Frons broad, widely separating eyes in both sexes." So if this is a conopid, it's definitely an aberrant individual.

However, I can't say with certainty this isn't a "conopid look-alike" in some other family. I did try to run it through the key to families in the MND(2), but there were way too many key couplets where the salient characters couldn't be assessed from the photo. So that point will have to be left to someone with more knowledge to ascertain.

But if we assume it is an aberrant conopid, then from the antenna (with terminal style) and basally constricted abdomen it keys to subfamily Conopinae in the MND(1), and to genus Physoconops...since a small triangular cluster of three ocelli are apparent at the rear edge of the vertex in the full-size image. (Physocephala lack ocelli.)

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