I'm not sure on what you based the color and hairiness attributes stated above for S. opinator...but from your comments below I'm presuming it was Martin's photos. Martin has now posted his male (and female) S. opinator images ...and everything looks well within reasonable limits color-wise (and "hair-wise") to me...click on the thumbnail to see his images:



Color discrepancies often arise from numerous factors, for example: impacts on photographic exposure and white-balance due to differences in lighting, and in contrast conditions with the background; flash-effects (especially for bright-white hairs...like those appearing on the occiput and the lateral edging of the frons in my photo); aging of specimens and/or the effects of chemicals used in capture & storage; and...of course...plain old natural variation!!

Bill, as a summary response to many of the observations you've made concerning this post...in your numerous comments both below and above...there are two key things to consider:

1) How taxonomically significant is the given character trait?2) What degree of variation might be present in that trait, when considered over a population of a taxon?
These two questions are fundamental. And addressing them is, unfortunately, fraught with all sorts of opportunities for ambiguity and subjective disagreement. Such ambiguities and disagreements are the source of a large part of the headaches endured by those of us interested in taxonomy!

I do appreciate your observational finesse, and the constructive value of many of your remarks on this post. But, with all due respect, for some of your remarks I submit that you'd benefit from reflecting on the relevance of the two questions listed above.

We're dealing here with actual biological individuals...which are prone to all sorts of modes of variation and do not give a whit about conforming exactly with every restrictive character trait a human taxonomist might wish to impose in order to fit some preconceived category in the scheme of that human's taxonomic conventions. Members of a biological species are not necessarily identical to each other, nor to their taxonomic representatives within an idealized typological framework.

In addition to the male "Western Forest" and female Univ. of Alberta images you referred to, here are a few more photos links: a male and female in this 2008 UC Davis publication; a female on UC Davis web page; various specimens from BOLD; a male & female in Fig. 4d and a female in Fig. 5a from a 1924 paper (captions for those figures here); and a female image here.

For all the above images, it's hard (or impossible) to discern most the distinguishing nuances gleaned from Vockeroth(1) that I mentioned in my (long!) comment below for separating S. opinator from the troika of Eupeodes (Metasyrphus) species (americanus, fumipennis, and pomus). And separating S. opinator from S. intricatus for any BG posts other than technically pre-planned, high-magnification images will likely not be feasible.

I was unsuccessful in searching for images of Osten Saken's type for S. opinator, and I couldn't even figure out where it is (perhaps at the MCZ?). But there may be paratypes in various collections in the US and Canada, and there must be lots of curated museum specimens.

Researching things for this post drove home to me how difficult and esoteric this group can be. I wasn't aware there were so many very similar looking but distinct taxa at both the generic and species level...and that they were separated by so many seemingly subtle and sometimes arcane characters. I looked at the entries for Syrphus, Metasyrphus and some related genera in the 1965 catalog by Stone(2) and was amazed at the number of taxa listed! Many must have been put in synonymy in recent decades, and I'm guessing most determinations in museum collections may be old and have lots of different names attached to them. The taxonomy of this group is much more difficult than I had thought, and getting a clear handle on its diversity, distinctions, and relationships would be quite a challenging undertaking!

You are right Aaron, the Syrphini are the most difficult group of the Syrphids, and it is very difficult to even get to genus without having the specimen under a microscope.... I spent a lot of time working my way through these flies and even with microscope etc I have not been able to ID every specimen... so don't feel bad about not being able to ID pictures!

Thanks for your consolation and encouragement here :-). Trying to piece together a solution to the problem of clearly separating Syrphus opinator and Eupeodes americanus...based on keys and descriptions from the literature but without being able to discern the "lower calypter hairs character"...is looking more and more tenuous. I think I've advanced significantly in that labyrinthine game, unfortunately ending with what seems to be just a smidgeon short of stalemate.

If we take the hypothesis that my post here is Eupeodes (Metasyrphus) rather than Syrphus, then it keys in Fluke(1952) to Metasyrphus lebanoensis via the couplet sequence: 1→3→39→40→44→45→46→47→48.

Recently, in addition to Fluke(1952), I found two earlier papers by that author: Fluke(1930) and Fluke(1933). My post also goes to M. lebanoensis in the key of Fluke(1933), and the original description appears in Fluke(1930)...it can be read here.

The key and description, make clear that S. lebanoensis, which is currently synonymized with E. americanus, has:

    1) the yellow spots on tergite II reaching the margin; and
    2) no dark medial stripe on the face.

Thus, when the calypter hairs character is not visible, it seems the only traditional separating character in this group that remains is whether the cheeks have black. In S. lebanoensis the cheeks are described as black, whereas in S. opinator the cheeks, along with the rest of the face, are entirely yellow.

Besides possible subtleties in the width and shapes of the tergal spots & bands...I don't see much hope for other more robust separating characters in the literature. Perhaps some of the many characters Bill has mentioned in his comments under this post (i.e. the bright white hairs or pollen along the lateral edges of the frons in the male) may be useful?

Eupeodes has most of the times black in the face, while Syrphus is all yellow (I just checked a few!), furthermore Syrphus looks way more "hairy" than Eupeodes and is in general a bit more lean and slender, while Eupeodes is more roundish and kind of "hairless", but this is just experiance and gut feeling... Also Syrphus has a bit more a dull thorax, while Eupeodes is shining. On top of it, I do not think that there is Eupeodes americanus in CA. Already Vockeroth siad that the CA records could be misidentifications of fumipennis, and E. fumipennis is next to volucris the most common Eupeodes I collected in CA. And S opinator is very common here on the W-coast. So from the small markings and everything I still think it is very plausible that this is opinator... but who knows?!

This specimen doesn`t seem to fit any likely Eupeodes in the key. It does key to S. opinator if we accept that it is Syrphus. It would mean that this is a very, very variable species and following Martin`s comments I am thinking it could be S. opinator. I have never seen this species, however. Aaron is to be applauded for the fantastic research he has done.

I can certainly make errors, and appreciate correction when that occurs. Perhaps this is Eupeodes? It does look similar to the thumb below:



However, it looks equally close to the current posts under S. opinator. Perhaps some or all of the above are mis-IDed? We can all...amateurs and experts alike...make errors (or sometimes become too over-confident and cavalier!).

But are you certain hairs on the calypters can't be seen in my photo? I'm pretty sure I see them. Look carefully at the full-size version of my image above...and reread the last sentence of the 2nd paragraph of my remarks posted below the photo. Then compare with Fig. 62 on pg. 730 of the MND(1), where the hairy lower calypter is shown from a more transverse viewpoint (in contrast to the more vertical view in my photo). I definitely see hairs on the calypters in the full-size version of my image. And if my interpretation is correct, I think they're on the lower calypters...and that the upper calypters are the relatively bare "small ovals" tucked between the hairy lower calypters and the dark edge of the wing just above the base of the (downward-folded) alula.

I was in the process of considering your original comments and cross-referencing with other resources before you completely rewrote your comment above (your edited version now basically repeats that which you posted under the 2nd image here...so I won't respond there).

Your original comment asserted I'd misidentified this post, and that it's a Eupeodes species, which may well be the case. But you indicated this couldn't be S. opinator because males of that species have characters you saw as inconsistent with this individual: e.g. hind femora black except at tip; mid-femora black on the lower half; and frons with yellow above the antennae.

However the view of the frons in the image above...and of the hind and mid femora in the 2nd image of the series...seem more or less consistent with the characters you pointed out, so those characters would seem to lend more support to a putative ID of S. opinator. (Perhaps that's why you edited that out of your original comment above?)

You also gave a reference to the Bull. of U. S. Geological Survey and a page number,...but no author, title, volume, or date! (I couldn't get very far with that incomplete citation...could you give more info, or better yet a link?)

I am 100% certain you can`t see the hairs which are mentioned in the key. I`ve looked at the enlarged image. The hairs you are seeing are the fringe hairs at the edge of the calypter which can be seen on all Syrphidae. To see the hairs, the wing has to be pushed forward so the calypters will separate. The hairs are on the middle of the lower calypter and difficult to see on a photograph.
I found the Bulletin on Google, typing in Syrphus opinator United States National Museum -
https://books.google.ca/books?id=fMc9AQAAMAAJ
Your specimen has the hind femora BROADLY yellow-orange and the anterior femora are much less than half black, half black in S. opinator ( the mid femora could even be almost entirely orange in this specimen ) and in the lateral view is that a flattened beading at the side edges of tergite as in Eupeodes but not in Syrphus ( not clear )?
I have never seen Syrphus opinator or a picture that I know for sure is correctly identified. As far as the other pictures of Syrphus opinator by Ron Hemberger, they are probably incorrect too. The bulletin says the thorax should be metallic bluish green, the front above the antennae yellow with black hairs and the angle between the eyes greenish black - not in Ron`s picture and his picture also has the problem with the hind femora not being black accept tip. I haven't looked that closely at Ron`s pictures but my first impression is that they are Eupeodes sp.
I`m not certain with this specimen as features could be variable. Should we place it in Syrphini at this moment in time?

Bill, after studying this link, I see your point about the hairs on the lower calypter...even though the dipiction in Fig. 62 on pg. 730 of the MND(1) looks significantly different, and led me to believe that based on the representation of things in the MND(1) the character might be vaguely discernible. I'm not a longtime sage on all things syrphid...but looking at the bigger picture...I honestly have to say that from my (perhaps naive) viewpoint the contrast in character states shown in this link seem like a fairly insubstantial basis for separating genera. (I have difficulty imagining a physiological or ecological function which might make those hairs a significant character to coherently select for over time in the evolution of a new clade.)

However, even if the appropriate calypter hairs character cannot be ascertained here, alternate avenues allow one to reach a reasonable resolution, as explained below.

Using the CJAI Key to Neartic Syrphidae (and Vockeroth(2), among other things) this syrphid can be narrowed down to either Syrphus or Eupeodes. If it's Eupeodes, then Table 3 of the checklist here (scroll down to near bottom) would imply subgenus Metasyrphus...as this is not E. volucris, due to the lack of paired "comma-like" (or kidney-shaped) spots on tergites II-IV and the absence of protruding terminalia for this male. By the way, Vockeroth(2) clearly states that members of both Syrphus and Metasyrphus share the character of a "distinctly margined edge" from around tergite II to tergite V or VI. I believe that's what you were referring to as a "flattened beading" on the lateral edges of the tergites...and it doesn't separate the genera here.

Bill, I'll address the specific comments & doubts you raised about S. opinator for this post in what follows...but first I'd like to note a few more things. The U.S. National Museum reference you gave is to Williston's 1886 "Synopsis of North American Syphidae". At that time, Williston treated (the then known) members of subgenus Metasyrphus as lying within the genus Syrphus rather than Eupeodes. And in his key my images unambiguously go to S. opinator via the couplet sequence 1→12→13→14→15→16→17.

Also, the bulk of the description in Williston is a verbatim duplication of Osten Sacken's original 1877 description of S. opinator. Osten Sacken's description was based on just 4 specimens from north of the San Francisco Bay area: 2 males and 2 females. Williston stated he'd seen nearly 50 specimens (male & female from California to Washington) which agreed "closely" with Osten Sacken's description.

I went through Osten Sacken's detailed 1877 description, character by character, and I would say that overall it is in close agreement with the individual in this post...modulo the normal discrepancies one usually encounters in such an exercise (i.e due to lack of accounting for possible variation within such a widespread and fairly common species; or confusion that can arise from an authors imperfect choices of words...which often entails ambiguously subjective perceptions of color!).

Now I'd like to address your comments. Let's begin with the femora. You indicated concern over a perceived discrepancy in the proportions on the femora of black to "yellow-orange" (or brown, or even better..."testaceous") vis-a-vis my photos and Osten Sacken's description. Such proportions are usually only approximate, and are often somewhat variable among specimens. But, more reassuringly, if you read the 1992 description of S. opinator in Vockeroth(2) (presumably based on consideration of many(!) more specimens than Osten Sacken or Williston examined), you'll find he states:

"Fore and mid femora with basal one-third black, apical two-thirds yellow...; hind femur mostly black, apical one-third to one-fifth yellow..."
The proportions of black on the femora in my photos are in good agreement with Vockeroth's description...thus, rather than constituting a discrepancy, they add yet further affirming characters to the list supporting a putative ID of S. opinator!

Secondly, you expressed concern about Osten Sacken's description of the frons...to quote him:

"Front above the antennae yellow, the angle between the eyes greenish-black, yellowish-pruinose beset, with black hair; small brown marks above the root of the antennae."
Again, much of this actually affirms a putative ID of S. opinator! A close look at the full-size image confirms that the frons is mostly yellow; with black hairs; and with small brown marks above the root of the antenna. BUT...I agree the greenish-black part seems off. I do see a small bit of black at the apex of the frons...though I don't perceive any significant "greenish" tint (at least on this individual). Perhaps the "greenish-black" is referring to the underlying sclerite surface...and the yellow appearance of most of the frons (and the white on lateral edges of its apex) are the effects of pruinosity? For comparison, Vockeroth states: "Frons entirely yellowish, gray pruinose on upper half or less" and a University of Alberta S. opinator web page states:

"Males: The frons is either entirely yellow, or the upper half of it is dark gray and covered with a waxy, whitish powder (i.e. pruinose), with lower half of frons bright yellow."
These three descriptions seem slightly inconsistent here. This is typically what happens when one tries to piece together descriptions from different authors. I think it can likely and reasonably be attributed to a combination of variation within the species (which is the bane of the "typological" approach to taxonomy) and perhaps also variation in perception (and sometimes not entirely precise communication) by authors (i.e. "gray vs. white" pruinose on "upper half" vs. upper lateral edges of frons, etc.). But overall I think this is typical of how a determination from the literature proceeds, and on balance I'd call this a reasonable fit.

Thirdly, you brought up Osten Sacken's statement: "Thorax metallic-bluish-green, densely beset with yellow pile". On the affirmative side, dense yellow pile is clearly apparent on the scutum in the full-size lateral photo...but I definitely agree that, at least to my eye, the color of the thorax there looks largely "bronzy", not "bluish-green"! However, from the viewing angle in the full-size dorsal photo, there is a definite greenish cast in the well-lit central portion of the overall shining-black scutum. I think the discrepancy in thorax color between Osten Sacken's description and the photo here (and perhaps other posts as well) may arise from a number of factors. For instance: 1) possible interspecies variation; 2) angle of view, i.e. in my lateral view, the bronze-colored appearance is likely caused by fine yellow pruinosity overlaying the black (and ever so slightly greenish) substrate; 3) differing subjective perception of color among individuals (you may find this last item suspect, but I know a number of botanists who are color-blind in various spectra...and am aware that has had repercussions in some botanical keys!). I read a number of authors comments on S. opinator, and none of them mentioned (let alone emphasized) a "bluish-green" color for the thorax. The closest thing to this was in Vockeroth's genus description for Syrphus...where he stated: "Scutum shining to subshining, blackish green; sides of scutum and all pleura distinctly yellowish or grayish pruinose". This seems consistent with my image, and with this Univ. of Alberta female image. The female image here from the LA County Museum collection shows a black thorax with a touch of greenish tint. A more clearly "greenish"-black is evident in the images of other Syrphus species at this link. (BTW, note that, unlike S. opinator, the species in that preceding link have yellow bands on tergites III and IV that reach the margin of the tergite).

Overall, I believe the discussion above yields a good case for Syrphus opinator (which, by the way, has records Marin Co. and other locales surrounding where I found this individual). Nevertheless, to more thoroughly vet the question I carefully went through the keys to species for Eupeodes (Metasyrphus) in both Vockeroth(2)(1992) and Fluke(1952). In doing so I was able to account for all 20 species listed on the Metasyrphus species list from 2013 here. Following all key leads whenever the photos didn't allow for characters to be discerned, most of the 20 species could clearly be eliminated by character conflicts apparent in the key breaks. This left only three putative species: pomus, americanus, and fumipennis...all of which are very similar-looking to each other (and to S. opinator) in cursory gestalt.

Separating males of those three species in the key depends heavily on details of genitalia and microsetulae of the wings...characters not visible in typical BugGuide images. (And Vorkeroth's key and descriptions indicate females of those species can't be distinguished.) But upon reading the male's descriptions, all three candidates have the following discrepancies with the individual in my photos: 1) all have the yellow spots of tergite II not reaching the outer margin; 2) all have black or brown on their cheeks; 3) all have a dark medial stripe along the forward edge of the face (i.e. below the antennae). Vokeroth lists E. americanus and E. fumipennis as occuring in California, but not E. pomus. They also have subtle discrepancies in the details of the yellow maculations on the tergites III and IV. . For instance, in S. americanus the yellow bands of tergites III and IV of S. americanus are quite broad...more than half the front-to-back breadth of their tergites (see full-size image here). In constrast, reference figures for S. opinator, indicate the yellow bands on tergites III and IV are much narrower...more like a third of the front-to-back breadth of their tergites (which is in excellent agreement with my photos).

Finally, I should reiterate a point made in my original remarks with this post: without being able to view the microscopic setulae of the wings, is seems one can't distinguish S. opinator Osten Sacken 1877 from S. intricatus Vockeroth 1983. However, Vockeroth(2) indicated they may both be part of a single variable species...and if so, clearly S. opinator would have nomenclatural priority. Furthermore, while both are recorded from California in Vockeroth(1992), it seems from the literature that S. opinator is the more common species in CA...though that impression could be an artifact of it being the better known alternative over decades of (possible mis-)identifications. So, while I'm fairly confident that S. opinator is the most appropriate ID here, it would be more taxonomically cautious to place this under a joint "S. opinator/intricatus" guide page.

My goodness you have been busy and I have been reading too. The amount of black on the femora apparently is very variable. I have been in touch with Martin Hauser who has S. opinator in his collection and he has sent me some photographs. Seeing his pictures there are a number of features which show your specimen not to be S. opinator. I am hoping Martin will post his pictures on Bugguide. At this moment in time I will mention one feature. The angle formed by the eyes of the male on the frons is only about 80 degrees in his picture whilst your specimen the angle is obtuse.
It does key out as S. opinator but only if you have assumed it is Syrphus and not Eupeodes. The beading is very restricted in Syrphus whereas much more complete in Eupeodes. Martin`s pictures show the tergites clearly rolled; the colour of hairs behind the eyes are diferent, the colour of the pleurae are different, the hairs on the sternopleura are quite sparse compared to yours. The hairs at the top of the head are restricted in your specimen not in Martin`s picture. The black hairs along the sides are much more pronounced in your specimen. I think when talking about the angle between the eyes, he means the ocellar triangle. The frons is totally yellow in Martin`s specimen. The feature of the hairs on the lower calypter is the MOST, MOST, MOST important feature in identification and can`t be overlooked and is the ONLY, ONLY reliable feature separating Syphus in the Syrphini. If you know where to look, this is not a DOUBTFUL feature. Impossible to see unless the calypters are separated. Syrphus opinator has only the sub costal cell, ( the costal cell contrasting with it ), and the cell before the humeral cross vein and two cells below it at extreme base of the wing infuscated with the rest of the wing hyaline. Your specimen has the wing widely infuscated. In you specimen the markings on tergite 2 are very much cut away behind and narrowing towards margins whereas S. opinator has this marking more parallel and reaching the sides more broadly. The picture of S. opinator has black hairs on the frons and at the sides of the antennae but they are thin and sparse whilst your specimen has thick hairs and more dense, looking very different.

...the photographs you refer to from Martin's collection...though I still have a number of hesitations.

For instance, the 80° opening angle for the male frons doesn't agree with the published images in the "Western Forest" book; or this 2008 UC Davis publication; or this 1924 Bull. of So. Cal. Acad. Sci. paper.

Moreover, you also stated: "It does key out as S. opinator but only if you have assumed it is Syrphus and not Eupeodes. The beading is very restricted in Syrphus whereas much more complete in Eupeodes. Martin`s pictures show the tergites clearly rolled".

I'm assuming your use of the term "beading" here refers to the "thinly-crimped" common edges of adjoining tergites & sternites...which is often visible as a string of bead-like specular highlights along the lateral edge of the abdomen. That crimped, beaded, lateral edge is what I understand the phrase "abdomen margined" to mean for these genera. In that context, I presume the character "tergites clearly rolled" is in opposition to that of "abdomen margined".

But the genus descriptions in Vockeroth(1992) state (green emphasis mine):

For Eupeodes, on pg. 94: "Abdomen oval, usually nearly flat above, with strong margin from near middle of tergite 2 to apex of tergite 5."
              ...and...

For Syrphus, on pg. 363: "Abdomen oval, moderately broad, slightly convex above, distinctly margined from about middle of tergite 2 to apex of tergite 5 or 6"
The above would seem to indicate that the "beading in Syrphus is generally more complete (i.e. up to tergite 6) than in Eupeodes, rather than more restricted. Thus don't Vockeroth's genus characterizations seem to conflict with a S. opinator specimen having tergites clearly rolled (= the opposite of margined)?

And regarding another character you expressed concern about, namely that: "The black hairs along the sides are much more pronounced in your specimen" — check out the 4th image I recently posted here. In that image, Fig. 201 for S. opinator from Vockeroth, appears to be completely consistent with those straight, outwardly-pointing black hairs in my photo. Regarding the other details you mentioned in your comment, I think they may be of interest...but at this point, I don't have any clear basis for evaluating their relative diagnostic significance for species determination.

BTW, do Martin's photos clearly show the lower calypter hairs character? Given that you've indicated it's impossible to see that crucial character unless the wings are spread forward...and assuming the bulk of pinned, dried specimens (let alone field images!!) may not be so positioned...I can imagine folks might frequently bypass the difficulty of checking that character. One then has the challenge of avoiding a mis-ID in trying to use the alternate characters I've been attempting to employ to separate the very similar-looking and easily-confused taxa among S. opinator/intricatus and Eupeodes americanus and friends. Numerous possible mis-ID's compounded over time may have created a mess in terms of name usage here!

Thus, for the purposes of photo ID on BugGuide, it would clearly be very helpful to get the details of how to distinguish S. opinator/intricatus and E. americanus straightened out and clearly presented (if possible!), especially considering many references state these are both very common and widespread species throughout the US & Canada...and we likely have a whole lot of currently unplaced (and/or misplaced) posts for this "opinator/americanus" complex at various nodes under Syrphini. For example, consider the post below, suggested as possibly S. opinator by Wouter van Steenis:



So far, scrutinizing everything in our comments, with an emphasis on the published literature, my best shot at the ID here is still S. opinator...though that may be in error, and I don't mean to be intransigent (like you almost seem to be in repeated asserting in can't be! :-) I would change my opinion if I could see clearly supportable and incontrovertible evidence indicating otherwise by studying bonafide S. opinator material, and/or viewing Martin's photos and getting further pertinent info from him and/or other experts. I'll try to study specimens at the CAS and Essig museum if I get a chance in the coming weeks too.

So I added the pics I took for Dean and placed them under opinator, a species very common here on the West coast.
The specimen Aaron photographed looks to me like opinator, but this is more a guess than a fact. Syrphus species have a strangely dull thorax, while Eupeodes are more often polished and shiny. But this can be influenced by light and angle a lot! There are a lot of good arguments and interesting characters evaluated... I wish I could join in a bit more, but I have more than 20 drawers full of flies, which need an ID, so I can not spend too much time of photo ID's, which might not be possibly identified to species in the first place.... Aaron, you are always welcom to take a look at the CDFA collection whenever you want...(of course Bill is also invited, but he lives further away, and therefore is less likely to stop by). I hope the pics I posted help a bit...Cheers
Martin

Those are three fine photos in your post:



Good angles, excellent lighting, focus, resolution, and presentation of diagnostic characters!! (Wondering if it was formed from multiple stacked images?)

I must say I'm surprised at how pale (nearly white!) the face, venter, and tergal fasciae are! And also the reddish tint in the ground color of the tergites. I wonder if the fresh specimen had those colors, or if they're might be (at least partially) an effect of aging, and/or chemicals present in a storage cabinet or in a killing jar?

I think I can see the hairs on the posterior end of the dorsum of the lower calypter in the 2nd photo. However, I can't discern the pertinent hairs in the 3rd image, it almost looks like they're absent from the posterior end of the dorsum of calypter there...though I see plenty of hairs on the edge. Easy to misinterpret those edge hairs, what a tricky character!

Anyway, nice to have the calyter hairs visible...that eliminates the biggest nagging ambiguity of IDing members of what I'd call the "intergeneric opinator/americanus complex". Your post confirms that there's no dark medial stripe on the face, and that there's absolutely no dark color on the cheeks...which is the main character I ended up with for diagnosing S. opinator over E. americanus when the decisive info on the calypter hair character is lacking.

BTW, I see from the dichoptic eyes your specimen here is a female...which I think may account for a number of the discrepancies Bill had pointed to between my photos and yours (under his apparently mistaken notion that it was a male). In particular, the 80° opening of the frons, and it's yellow lower half and grey pollinose upper half; the shorter outward-spreading hairs along the abdominal margin; and the length & amount of shaggy hairs along the forward edges of tergite I...those are all likely sexually dimorphic. characters. For instance, compare the female abdominal figures in the top row of the following post with the males abdomens shown in the 2nd and 3rd rows:



Would love to similar photos of a male S. opinator.

The specimen is a bit lighter and off colored because it was caught in alcohol and then chemically dried with HMDS (http://phorid.net/hmds_index/)which lets them appear more "clean" and more pale, because they are lacking all the oils in the body... The picture was one of the first ones I took with the Olympus tough F 2.0, which has a microscope setting with automated stacking... works rather well and is quick. The lighting was with a self build light dome, which gives very nice and soft light, and makes the "dust" pattern very clear.

Just noticed you posted a trio of images of the male too!!



My wish come true...talk about immediate gratification!! Thank you "Santa" Martin :-)