Syrphid - Eristalis obscura

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Home » Guide » Arthropods (Arthropoda) » Hexapods (Hexapoda) » Insects (Insecta) » Flies (Diptera) » "Aschiza" » Hover Flies (Syrphidae) » Eristalinae » Eristalini » Eristalina » Drone Flies (Eristalis) » Subgenus Eoseristalis (Eristalis Subgenus Eoseristalis) » Eristalis obscura

Photo#463564

Copyright © 2010 Aaron Schusteff

Syrphid - Eristalis obscura -

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 perplexing...at least for me! (See my response to Ron's comment below).

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Contributed by Aaron Schusteff on 10 October, 2010 - 2:52pm
Last updated 9 October, 2014 - 8:35pm

Moved

Moved from Eristalis.

… Martin Hauser, 9 October, 2014 - 8:36pm

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.

… Aaron Schusteff, 9 October, 2014 - 11:30pm

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)...

… Martin Hauser, 10 October, 2014 - 9:36am

Moved

Moved from Syrphid Flies.

… Aaron Schusteff, 11 October, 2010 - 2:59pm

Eristalis. but I don't know species

It's a female. Note eyes touch on male:

… Ron Hemberger, 11 October, 2010 - 12:27pm

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.

… Aaron Schusteff, 11 October, 2010 - 2:01pm

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.

… Ron Hemberger, 11 October, 2010 - 4:40pm

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