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Photo#318827
Bee Fly, cf Geron - Geron

Bee Fly, cf Geron - Geron
Stevens Creek County Park, Santa Clara County, California, USA
August 10, 2009
Size: ~ 6-8 mm
Fly at lower left is smaller, darker and has stubbier wings, but could be same species as that in upper right (out of focus in this shot). Reason: wing venation very similar, possibly identical; aristae and red eyes (hidden in this view) are similar; same long bombyliid-like legs; several of each morph feeding together on pennyroyal. The first two of the linked shots were taken one second apart; the third shot, my #4693 was taken nine seconds later and may be a different individual.

Images of this individual: tag all
Bee Fly, cf Geron - Geron Bee Fly, cf Geron - Geron Bee Fly - Geron - male

Progress towards species ID
I've just been working on IDing some photos I took of a bee fly in the subgenus Empidigeron (not far from your locale here). Here's some of what I've learned...

Six species of Empidigeron are recognized in the 2003 catalog by Evenhuis & Greathead(1), and the same 6 species are treated in Painter (1932) (at the end of his key ...couplets 21 through 27 on pg. 146). Descriptions for all six species are also given in Painter on pp. 162-165 (though some aren't as helpful as I'd hoped for....I'm having difficulty correlating parts of the descriptions consistently with images of specimens on BugGuide.)

The catalog of Evenhuis & Greathead(1) indicates that only two species occur in CA: aequalis and hybus. The former has 1st and 2nd antennal segments nearly equal (hence its epithet), while the other five species have the 1st antennal segment about twice the length of the 2nd...which is what I think I can make out when I zoom in on your 2nd image of the female.

Painter's description of hybus (on pg. 165, actually a copy of Coquillett's) also states, among other things, that hybus has:

    1) "knobs of halteres light yellow" (checks on both your flies...though that's fairly common in flies!);
    2) "two (black) spots on the the upper part of the occiput" (which I think I may see vague indications of in the female in your 2nd image...buried underneath some pile. The other's occiput seems all black.);
    3) "two (black) stripes on the thorax" (hmm...yours are closer to dark brown on the plump female, and this doesn't seem to match narrow black one); and
    4) "...tomentum on upper side of body of female yellow (wanting in male). [Bold emphasis is mine.]

If the narrow black fly is indeed a male of the same species, then item 4) above seems to positively address the question explicitly raised in my earlier comment from 11/26/11 below (i.e. regarding sexual dimorphism in color, an observation perhaps implicit in your original remarks).

One other thing, the key on pg. 111 of the 1894 work of Coquillett, where he described G. hybus, states that G. hybus has "abdomen slender, nearly four times as long as wide ". That seems to be the case for the narrow black one in your post, but not quite for the female (and even less so for my post of a putative G. aequalis). Then again, Coquillett used the wiggle-room word "nearly"...so maybe your female is OK in this regard.

On the other hand, the key of Coquillett implies hybus has all femora black (your female has hind femora yellowish) and Painter's key implies hybus has the middle tibiae yellowish and lighter than the rest (holds for your female, but not the other one). When I read the entire description, I seem to be running into other inconsistencies as well (or "ambiguities" for those who prefer euphemisms :-). I don't know what portion of those inconsistencies arise from error (mine and/or the authors) and how much comes from the inevitable disconnect that variation in "biological species" forces upon the "typological species" concept us neo-platonists try to impose on nature's organisms :-) But if there are indeed only two species of Geron in CA, as circumscribed in the current literature...then at least the female here is likely G. hybus.

Male and Female?
Could the color and size difference here be due sexual dimorphism?

 
Male and Female?
Probably. The skinny one appears to be a male based on the tip of the abdomen (Geron have externally visible genitalia unlike many other bombyliids), and the males in the genus are usually thinner. If you saw the top of the head that would clinch it, as males are always holoptic as far as I know.

Moved
Moved from Geron.

Moved
Moved from Bee Flies.

Moved
Moved from ID Request.

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