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Syrphid - Eristalis obscura - female

Syrphid - Eristalis obscura - Female
Wilder Ranch State Park, Santa Cruz County, California, USA
March 20, 2010
Photographed on flowers of Death Camas (Zigadenus fremontii).

I tried to key this in the "Manual of Nearctic Diptera"(1) but was having difficulties at various junctures. So I began searching through BugGuide images and found Eristalis dimidiata to be a good match. I then worked backwards through the key from Eristalis and, disregarding couplets involving things I couldn't see in my images, satisfied myself it was a likely candidate.

I think this may be a male, as the first break in the Syrphidae key in the "Manual of Nearctic Diptera"(1) (on pg 718) states "Male abdomen with tergite 5 not visible in dorsal view" for members of the subfamily Eristalinae.

Correction on 10/11/10: Apparently this is a female, from the separated eyes. It seems counting visible dorsal tergites for this (and other Eristalis) can be very least for me! (See my response to Ron's comment below).

Images of this individual: tag all
Syrphid - Eristalis obscura - female Syrphid - Eristalis obscura - female

Moved from Eristalis.

Thanks, Martin
Guess this was the 1st BG post of this species :-)

I'm wondering if it's an introduced species? I couldn't really tell from a first quick look at Hull (1925)...but there are probably more recent ref's.

Yeah, it was new for BG, Bill
Yeah, it was new for BG, Bill Dean went and identified it, and I confirmed and moved it. It is a holarctic species, but it is a northern one, and native to Canada and the northern US. It is difficult to ID just from pictures, and it is mainly in the north, so it took a while until Bill got confident enough to ID most Eristalis, but we found a few more specimens, which is really great (and doing so we found interrupta, which is also new for BG)...

Moved from Syrphid Flies.

Eristalis. but I don't know species
It's a female. Note eyes touch on male:

Thanks for the info Ron!
Guess mine's a female then!

I think I counted abdominal segments incorrectly. I just learned that's an easy error to make...while studying Herschel Raney's (wonderfully) illustrated key to Eastern Syrphidae.

It turns out that in Syrphidae:
1) What appear to be terminal tergites are often actually sternites; and
2) The 1st abdominal tergite is often exceedingly thin!

For illustrations of the above, see this diagram, or this diagram, or this one, or this one.

I just looked at a bunch of BG Eristalis images and I couldn't really make sense of the "abdominal tergite count" character for determining gender. That character is mentioned in the first break of the syrphid key in the "Manual for Nearctic Diptera"...but I guess eye separation is a far easier character to use!

I'll mark this post as a female.

Glad to help
Strictly a non-scientist, I work from observation and am not up on names of bug parts. The eye thing works with most syrphids and is usually easy to find out which by posts here.

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