Thanks to all of you for your kind comments. It feels good to be in the company of fellow nature lovers--and even some fellow fly fishers.
There is another facet of this story that is quite interesting to me, and maybe it will be to you. There is a big gender difference in the size of mayfly eyes, with the male's being much bigger, as hopefully you can see in the next image that I'm attaching below. Compare to the females in the pictures in my initial post. The theory usually offered to explain it is that mating occurs in swarms in the air, with males typically staying low and looking upwards to identify and approach females. Thus, supposedly, their eyes have evolved extra size and resolving power for that purpose.
Beyond size, in some families of mayflies, the eyes of both sexes actually change color between daylight and night. For instance, when this species first emerges from the water, it has eyes that are almost black. They soon turn to the yellow-green color that is apparent in the images above. As darkness falls, the eyes go dark too, and then lighten again the next morning. I have never read a good hypothesis for why this occurs, but it is very striking.
Image 4. PED male dun with big black eyes, freshly netted from the water surface. Shot several years ago, Canon 5D, 100mm macro lens.
Peter: No, although I've heard great things about the Olympus 50mm lens you are using, the new lens that I'm now testing with my E-M1 is the one that Olympus designed specifically for the micro four thirds format, the 60mm f2.8 macro; and it focuses all the way to 1:1. It has also received excellent reviews for the quality of the images it delivers; for instance see Ming Thein's review at
http://blog.mingthein.com/2012/09/21/olympus-60-2-8-macro/. The main thing that I have been concerned about is that some users have complained that its manual focus ring is a "by wire" design, so that it's hard to know where you are in the focus range, and thus difficult to use in the field at macro range. I'm finding that manual focusing does take some getting used to, coming from the Canon, but once you get the hang of it it's not too troublesome.
Both my Olympus and Canon macro lens focus to 1:1 reproduction ratio, but because of the 2x crop factor of the Olympus camera, an insect like this one almost fills the frame at 1:1 focus, whereas with the Canon it only fills about half the frame. This is generally an advantage in capturing more small details, but 1:1 focus in the Olympus is at a scant 3 inches, which frightens many bugs a lot more than the 6 inch distance of the Canon. Of course I can just focus the Olympus at 1:2 and get the same size image as with the Canon, and be back at about 6 inches again.
In insect photography, one thing I look for of course is how sharp the lens is, detail that can be captured, and how the depth of field plays out. All those look very good to great with the Olympus lens. At 1:1 macro distance, images are rendered very sharp up to a nominal f5.8, falls off modestly at f8, and is still quite usable for many purposes at a nominal f11, if you really need to reach for that extra depth of field. The next two images below are 100% crops of two similar 1:1 macro focus exposures, differing only in aperture setting. Both are identically capture-sharpened in LR, but not output sharpened.
Image 5. PED female spinner, f8; 1:1 macro distance (~3 inches from front lens element), 100% crop.
Image 6. PED female spinner, f11; 1:1 macro distance (~3 inches from front lens element), 100% crop.
Another quality of a macro lens that is very important to me is how it renders out of focus areas. I'm very happy with how this lens does that. See the flower shot below for a wide-open aperture example, as well as the vegetation backgrounds in the images in my first post, which were about 6-15 ft. away and shot at f5.6 (image 1) or f8 (images 2 & 3).
Image 7. Flowers at near 1:1 focus distance, f.2.8. White flowers are about 5mm width, against a large yellow flower in background.
So I'm pretty excited about the new lens, and having lots of fun trying it out on various subjects.