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Photo#1329146
cool fly - Eulonchus marialiciae - male

cool fly - Eulonchus marialiciae - Male
Canaan Mountain, Tucker County, West Virginia, USA
June 4, 2015
In sphagnum dominated fen

Moved
Moved from Ocnaea.

This is a significant range extension for a rare Eulonchus
Revisiting this post, I realized we erred earlier in taking this for Ocnaea. It appears it's actually the relatively rare Eulonchus marialiciae...which has unusually long & widely-flattened antennae for a Eulonchus (making it more easily mistaken for Ocnaea).

Eulonchus marialiciae is also distinctive in being the only eastern U.S. species in the genus (see map here). Moreover, studying the literature (e.g. Borkent et al(2016) and Adler et al(1997)) I could find just 9 records of distinct collection locales...which I mapped (including yours as "icon I") at this Acme Mapper link. Studying that map will show that all the previously recorded sites are within about 40 miles of each other in the Great Smoky Mountains of western North Carolina...while the locale here is about 320 miles to the northeast. That's very encouraging, as it suggests this species may be present over a much larger portion of the Appalachian Mountains (and perhaps beyond) than previously known. Adler et al(1997) mention that one larval host for E. marialiciae, the folding trap door spider (Antrodiaetus unicolor), ranges at least from Alabama to Pennsylvania. (BTW, there's a remarkably detailed treatment of that mygalomorph on pp. 271-284 of Coyle(1971)...and on it's relationship to E. marialiciae on pp. 281-282.)

I happened into this post again while studying other Ocnaea, and what made me reconsider the ID was the metallic-green body, almost entirely yellow legs, and the rather uniformly cylindrical abdomen (it's usually more "globular" in Ocnaea). What clinched the correction to Eulonchus was scrutiny of the wing venation. Note the difference in the comparative position of the vein "R5" in the wing venation diagrams for Ocnaea and Eulonchus, respectively, below (you can click to enlarge if desired):

Ocnaea             Eulonchus    
If one closely examines the photo in this post (it helps to "zoom in" using your web browser, e.g. by simultaneously pressing "ctrl" and "+" on your keyboard, repeatedly) it becomes clear that vein R5 bends upward and reaches the wing margin near the wing apex (as in Eulonchus), rather than bending downward and reaching the margin far below the wing apex (as in Ocnaea).

It's also interesting that you found the Eulonchus in a sphagnum dominated fen...since the only other current BugGuide post of E. marialiciae was similarly found on a "moss mat":

   

Eulonchus have a long proboscis, and the western species are often found nectaring on flowers. But Alder et al(1997) reported that during their concerted search efforts (spending 42 days over 2 summers visiting 43 sites along the Blue Ridge Parkway in North Carolina) they observed a total of just 10 adults visiting the flowers of smooth blackberry, Rubus canadensis (plant images & info here & here). On the other hand, Coyle(1971) reported finding on August 1-2, 1966: 18 adults flying around burrow aggregations of the folding trap door spider Antrodiaetus unicolor, as well as one freshly-emerged adult vibrating its wings within a burrow, and a pupa within a burrow that produced an adult a few hours after being found. Numerous abandoned pupal skins of E. marialiciae and host spider remains were also found amidst the A. unicolor burrow aggregations. So it seems the presence of burrow aggregations for its larval host A. unicolor may be a better predictor for the presence of E. marialiciae than the floral resources used by adults. The post of A. unicolor below appears on a "mossy mat":

   

And while Coyle(1971) indicates the trap door spiders don't build their burrows in flooded habitat like a fen, he states they do like cool, humid, forested areas with stable, inclined ground (for instance mossy banks without too much leaf litter)...and presumably such habitat exists nearby the fen here.

Many other acrocerid genera have vestigial mouthparts and do not visit flowers...and are much less-commonly encountered by people. But given your sighting here, it seems a bit surprising that E. marialiciae hasn't been recorded before to the north of the Great Smoky Mountains. (Note the other current BugGuide post is from Mt. Mitchell, NC...which is about 50 mi northeast of the area for the previous collection records...it appears as "icon K" in this updated Acme Mapper link).

Moved
Moved from Small-headed Flies.

Antennae are diagnostic of genus Ocnaea here (in their position atop the head, and more crucially in their extra long, laterally-flattened shape).

Moved
Moved from ID Request.

Acroceridae?
It bears a resemblance to this one:



The experts will let you know if I'm anywhere close. :)

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