Perched on a bare twig of a tall shrub (about eye height) at the edge of an oak woodland.
At first sight I thought this was a small wasp. But once in focus under the macro lens I realized it was a conopid...my first!! I've been looking forward to seeing one for a while now :-). Unfortunately, it flew before I could get a 2nd shot.
Keying in the Manual of Nearctic Diptera
(1) begins fine since this fly clearly has a dorsal arista on its antennae (rather than terminal stylus)...so it's
not in the subfamily Conopinae. But I didn't get a wing venation shot, which is necessary for the primary character in the second step of keying (couplet 6). Trying both choices at couplet 6 leads to
Dalmannia, or to
Thecophora (or possibly
Myopa...but they typically have gena more than half the eye length, and this one's is equal). All three genera have "double bent" proboscis, as is subtly visible here: the "forward" basal segment is beige-ish, the "backward" second segment is (at least basally) blackish.
Both the Manual of Nearctic Diptera key, and the key in Cole
(2) refer to females of
Dalmannia having abdominal segments beyond 7th narrowed and produced forward...which appears to be the case here, though a clear view is blocked by the right hind tibia. Also,
Cole indicates that
Thecophora has "antennae longer than frons" (which is
not the case here) and that
Dalmannia are "yellow and black" (which
is the case here).
Finally, in the keys in Camras & Hurd
(3), the lack a wing venation shot again makes keying results ambiguous...but the ambiguity is narrowed down to a choice between three taxa at the species level...either
Occemyia(=Thecophora) luteipes,
O. modesta, or
Dalmannia blaisdelli. Of these three candidates, Camras & Hurd
(3) state (on pg. 43) that
O. luteipes & modesta intergrade, and the most compelling character leading to them is that their rear femora are more than two-thirds yellow. But what seemed to me more compelling are the following key characters of
Dalmannia blaisdelli:
1) Scutellum and humeri partly yellow;
2) Thoracic pile relatively short; shorter than arista;
3) Pile of dorsum of thorax predominantly black in the center, yellow anteriorly.
All these characters seem to fit the fly in my photo perfectly. Also, Cole (pg 337) mentions that
D. blaisdelli "is said to partial to wooded areas" and "the wings are typically smoky"...both of which apply to this fly.
All this would lead me to believe that this is most likely
D. blaisdelli...except that
this curated image of
D. blaisdelli shows the hind and fore femura
more than half black!. Since my fly has the hind femur more than 2/3 yellow, perhaps I have
Thecophora luteipes or
modesta?
Postscript (1/5/14): I just found Cresson's original 1919 description here. He describes the femora as sexually dimorphic: in the males black in the basal portion (as in the curated image referred to in the last paragraph above); and in the females "yellow except fore one above; and the hind one with a sub-apical ring". That agrees perfectly with the female in my image here.
