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Photo#574641
Ferdinandea croesus - male

Ferdinandea croesus - Male
Off the Pacific Crest Trail, near Buck's Lake Road summit, Plumas County, California, USA
July 18, 2011
Found on flowers of Prunus emarginata along a mountain trail through coniferous forest and montane chaparral.

The genus here is clear: beyond being a solid visual match to previously ID'd Ferdinandea posts, it keyed well to that genus in the Manual of Nearctic Diptera(1) and Cole(2) (modulo the apparent error in Cole's key at couplet 33 on pg 304, where one has to take the inaccurate "Eyes bare" choice to get to Ferdinandea...the MND(1) correctly states "Eyes haired" in their couplet 58 on pg 731).

Upon searching for resources to key Ferdinandea to species, I found two useful items: an 1887 treatment by Osten-Sacken, and a short 1924 article by Shannon.

Shannon recognized 5 species (as did MND(1))...adding one, F. aeneicolor, to the four species treated by Osten-Sacken. However, the ITIS Ferdinandea web page lists only 3 of the 5 species mentioned in Shannon, relegating the other two to synonomy with F. buccata. This appears to be in accord with recent work of Thompson and Skevington mentioned at the top of this CanaColl F. buccata web page. So I'm presuming the 3 currently recognized species are aeneicolor, buccata, and croesus. Of these three species, Shannon, Cole, Osten-Sacken (and other web resources) indicate that aeneicolor and croesus are species of western North America, while bucatta is primarily an eastern species.

The primary key character Osten-Sacken gave for F. croesus is "Arista black" (vs. "Arista reddish" for the other species). Shannon also mentions that F. croesus has arista black, while the other species have what he describes as yellowish aristae.

The primary key character Shannon gave for F. croesus is "Four notopleurals (setae)" (vs. 3 or 2 for the other species). While I believe I can see four setae near the notopleural region in some of my photos (especially in last two images of this series)...I'm not absolutely certain whether or not some of those may belong to different technical groupings of setae (partly from my lack of expertise, and partly from the various angles of the images).

Another key character mentioned by both Shannon and Osten-Sacken for F. aeneicolor and F. bucatta is the presence of dark rear margins on anterior abdominal terga (Shannon refers to 2nd & 3rd terga, Osten-Sacken to 1st & 2nd). These dark rear margins are said to be absent on F. croesus. The distinction appears to be borne out in these curated images of F. bucatta and F. croesus.

So, in the context of the image in my post here, all the above seems persuasive for an ID of F. croesus. And indeed, most (all?) of the current BugGuide Ferdinandea posts seem likely to belong to this species using these same criteria, e.g. arista black, lack of dark hind margins on anterior terga, and western N.A. distribution. While the number of notopleural seta would be good to verify, it's difficult to discern in most images, and (with some hesitation) I'm taking the other characters as sufficient basis for the ID here. As always, any corrections or confirmations will be greatly appreciated.

Images of this individual: tag all
Ferdinandea croesus - male Ferdinandea croesus - male Ferdinandea croesus - male Ferdinandea croesus - male Ferdinandea croesus - male Ferdinandea croesus - male

Beautiful photos
of Ferdinandea croesus!
I saw several recently near Sturtevant Falls, Santa Anita Canyon, San Gabriel Mtns., also a Chrysotoxum sp. Unfortunately, I didn't have the right lens with me.
Jim Hogue has found Ferdinandea croesus in our local mountains as well.

 
Thanks, Hartmut
They're subtly beautiful flies, with that dense, glistening, golden pile on the abdomen.

This LACM web page lists a record near Red Box, in the San Gabriel's...so guess it makes sense you'd see them around there. I guess they're fairly well-distributed in the west. I saw them high in the northern Sierra Nevada in my post here...and also at around 900' elevation along edge of dense coastal scrub on the San Francisco peninsula:


I wonder if they're a mimic of something like this:

 
I've seen the specimens
but had not seen a live one until recently:

The mimicry issue is worth pondering, but at this point I'd just be making wild guesses.
Since larvae are supposed to be found in sap runs, I'll keep an eye open for those.

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