Mayfly Family Ephemerellidae (Hendricksons, Sulphurs, PMDs, BWOs)

Do any of you entomologist types know the true color of the PMD spinner? Dorothea or excrucians. Where I fish in MT there are huge spinner falls, many spents are on the water in the morning and others fall again at various periods during the day. I'd like to tie some with egg sacks as I saw many in July but forgot what color they were. Thanks.

Your post on Ephemerella subvaria brought back some memories that might be of interest to some readers.
I got my master’s degree under Ed Cooper at Penn State in 1966. I studied the impact of low oxygen from Penn State’s sewage plant on the mayflies of Spring Creek. The plant mostly removed BOD (organic matter which causes low oxygen) by oxidizing it in a bacteria rich environment. But at that time the plant did not remove phosphorus (and nitrogen) which fertilized the macrophytic algae and other plant growth. There were far more macrophytes (large plants) in Spring Creek below the sewage plant entrance than above, and essentially no mayflies. What was there in the effluent that killed the mayflies? Mayflies put directly in the effluent did not die over a 16 hour day. But oxygen samples taken over 24 hours in summer showed a much greater variation below the effluent (from 16 ppm (or mg/l), 160% of saturation in late afternoon) to 3 ppm (30 percent saturation just before dawn) (vs 14 to 10 ppm, +- 20 percent saturation above the effluent.
I built a Rube Goldberg machine in the lab that would control the oxygen levels and temperature of control and experimental cages that each held 25 mayflies. The control would keep oxygen near saturation and the experimental one would lower the oxygen over 8 hours (the length of night in summer). Mortality was dependent upon both oxygen level and temperature. Virtually no mayflies would die if the oxygen was above 2 PPM (or mg/l) at 8 C, or at 4.5 at 20 C. Seventy five percent of larvae would die at 1 ppm at 8 degrees and 2.5 ppm at 20 degrees. So the mortality was much more if the temperatures were high. Hence most of the mortality would presumably occur in August when the high temperatures (20C) would increase the larvae metabolism and hence need for oxygen, but the water would hold less oxygen even before the night-time respiration of the macrophytes would reduce it much further (to only 3 ppm). Thus the low nighttime oxygen caused by excessive plant growth was a sufficient cause or the near total absence of mayflies below the sewage plant. Recognizing the aquatic impact Penn State started to use land disposal of its effluent which as far as I knew alleviated, and even stopped, the negative impacts on the mayflies. Can anyone verify this ? The otherwise well done “The Fishery of Spring Creek; A Watershed Under Siege “
By Robert F. Carline, Rebecca L. Dunlap Jason E. Detar, Bruce A. Hollender Has nothing on dissolved oxygen or aquatic insects. In my opinion we need much more of an ecosystems approach for streams (Which we are doing for Little Sandy Creek in N.Y.).


Now back to Ephemeralla subvaria. The title of the paper I published on this project (my first of nearly 300 publications) was:
1. Hall, C.A.S. 1969. Mortality of the mayfly nymph, Ephemerella rotunda, at low dissolved oxygen concentrations. J. Elisha Mitchell Sci. Soc. 85(1): 34-39 (M.S. Thesis, Pennsylvania State University, 1966).

Whoa! Ephemeralla rotunda? This was by far the most abundant mayfly in Spring Creek where I sampled! But I could not even find the name in your list. Also I had my samples verified by Burke, author of the authoritative "Mayflies of Illinois", and he said Well that’s what it keyed out to in my book”. (Talk about scientific ass covering! ) Well to make matters worse (as of 24 hours ago) my next girlfriend, Molly, at the University of North Carolina, loved the name of “Ephemerella rotunda”, the rotund one, which comes to think of it described her as well. I liked it too. But n’exist plus: where had the most abundant mayfly gone? Fortunately upon reading the rest of the post I found “Ephemerella invaria is one of the two species frequently known as Sulphurs (the other is Ephemerella dorothea). There used to be a third, Ephemerella rotunda, but entomologists recently discovered that invaria and rotunda are a single species with an incredible range of individual variation." Ahh neither rotunda nor Molly stood the test of time. So I assume what I called rotunda is still alive and well in Spring Creek as invaria. Again, can anyone verify that?

If anyone wants to follow up on the distribution and abundance of mayfly (or any other species) may I recommend: Hall, C.A.S., J.A. Stanford and R. Hauer. 1992. The distribution and abundance of organisms as a consequence of energy balances along multiple environmental gradients. Oikos 65: 377-390. I can send it if you cannot get it from google, which I think you can. (chall@esf.edu)

These mayflies look more like the Sulfurs I see on the Delaware system than the PMD's I see in Montana. The Montana mayfly has a distinct yellow leading edge to an overall light dun gray wing and the abdomen and thorax have a more light greenish/yellow cloration so how is it that Infrequens is now known as Ep Dorothea Dorothea?

4/21/14 - Fished the Brodhead today at the last park before last bridge on PA 191 - downstream of huge riffle section so is a great tretch for this species. I didn't get there until around 1:00 PM, took a nap and started fishing at 2:00 and there were still cornuta coming off sparsely but steadliy - until 3:30 PM. Sparse rises, but I was entertained. Is that normal or could it be because the water is unusually cold this year. Are the males and females of the same size or is one larger - and of slightly more pale coloration at take-off from surface? It almost looked to me to be two different flies, but I'm sure they weren't.

Looks like an imitation would be about a #10 or #8 dark brown nymph pattern. I'm down here in north Fla and trying to match the hatch in the far north central part of the state, mostly to fool the bream. Any ideas or help would be appreciated. I found two patterns so far that seem to work- a little brown nymph with a rusty brown/orange thorax(maybe this is a good representation of the E. Temporalis), and a size 12 buzzer nymph with black body, peacock thorax and white breathing filament. The bream seemed to agree with that choice. I would like to try and copy more local insects as I figure out what they are.There are dragonflies and damselflies and mosquitoes. I could start there.