Hi Sayfu,
Sorry for taking so long to get back to you, but I've been out of town for several days in important business meetings with Mr. Trout.:)
Sounds like you have the species worked out. Since the difference between E. albertae and Ecdyonurus simplicioides from a fishing standpoint is probably unimportant (they both look very close and emerge in the same fashion) it certainly isn't vital for fishing success to know which one it actually is.
Just for grins though, if you would like to know for sure which one it is there are a couple of things you could look for:
The easiest are nymphs - Check the cobble for ripe flat-headed nymphs. There wing-cases will be darker (though not so much as baetis and PMD's) and their undersides will take on the bright colors of the dun (the ones not quite ready, though lighter underneath as well, will usually be duller). Straight cream, or with a yellowish or pinkish cast are the most common. Two tails - albertae, Three tails - simplicioides.
The duns are more difficult as both are two-tailed pale flies. From a behavioral standpoint, it's been my experience that generally Epeorus species will spend a little time on the water making the duns often worth imitating. on the other hand, Ecdyonurus (prev. Heptagenia) species get off pretty quick and fishing the dry can often be pretty tough. You can also find Epeorus hatching in calmer water which is rarely the case with Ecdyonurus (which may explain why they want to get off the water so fast). As far as comparing their appearance goes:
Size - Both are about the same
Wings - albertae wings are plain. The wings of simplicioides can be as well though they are usually lighter. They can also have a very pale blotchy appearance or even more common dark crossveins giving them a slight (pale) window screen look. If they do, they are easy to tell from the alberts. I'm not so lucky in my neck of the woods.
Eyes - Epeorus are usually kind of a Dk. blue gray, the males are large and look to touch each other. simplicioides on the other hand are usually almost black, and separated in the males. Separation is more important as color may be "too close to call."
Legs - Epeorus will be similar in color to the top of the body and usually have a single little dot (not band) in the middle of its thigh on the front leg. The legs on simplicioides will usually be noticeably lighter than the top of the body and will be plain or with a very feint banding.
Bodies - To the naked eye, this can also be "too close to call". Both can be cream, pale yellow, or even "pink". One observation though is that I've seen difference in the male alberts that can be fairly dramatic (almost grayish), while the western lt. cahills, ginger quills, pale evening duns, yellow quills, pink lady's (whatever we decide to call them), (simplicioides) are usually the same color in both sexes with the orange or pink highlights of the males most often in the thorax area rather than the abdomen.
Timing - The alberts are an earlier hatch. I agree though, this isn't conclusive, especially this year. I saw some critters this weekend that shouldn't have been there according to the hatch charts. They must not read.:)
I'm not all that familiar with the S. Fork, but both Schwiebert (Nymphs) and Arbona (Mayflies the Angler and the Trout) report good Fall hatches of simplicioides specifically on the South Fork, so I wouldn't discount the possibility.
Regards,
Kurt
"It's not that I find fishing so important, it's just that I find all other endeavors of Man equally unimportant... And not nearly as much fun!" Robert Traver, Anatomy of a Fisherman