The Stream Doctor

October 13th, 2003

Email YOUR Questions directly to the Stream Doctor. This is your opportunity to get an experts professional opinion on anything stream related.

Here is a letter from John Claassen, the author of the article on mayflies which emerge as duns which sparked a great deal of interest here:

October 2, 2003
Dr. C. E. Cushing, Stream Doctor
105 W Cherokee Drive
Estes Park, Co 80517

Dear Bert,
A fly tying friend of mine has just indicated to me that my article on flathead mayflies has raised a question as to which of the heptageniids, if any, can emerge as duns before arising to the surface. has shared with me a copy of "the Stream Doctor" article dated 15 September in which the question was raised. The article that I wrote certainly implied that March Browns, Yellow Quills, and Blue Winged Red Quills all exhibited this behavior. I must say that I impressed that someone's diligent research on mayflies should take him to the New Mexico's Trout's web site searching for insights into fishing certain mayfly hatches. I am glad my article on heptageniids stimulated questions and motivated some to seek additional understanding. I am certainly challenged by the queries made by Mr. Shepherd and Mr. Pierce.

I am flattered that I may have been momentarily regarded as an authority on aquatic insects. Of course, nothing could be further from the truth. Although I have PhD credentials, the credentials certainly do not apply to the field of entomology. However, as a result of my scientific bent, I find myself simply writing articles on aquatic insects to increase my understanding of fly fishing and hopefully in the process, I will impart some insight to other fly fishing anglers.

Since I have only studied fly fishing for a limited time (almost a decade now), when I do write, I am careful to base my writings on sources that I regard more qualified than I. In this case my research into heptageniids led me to two sources which are cited at the end my article. One article I suspect was written by the resident entomologist at the McCloud Preserve in California. His name was not disclosed in the McCloud Preserve newsletter. The other reference was written by Jim Schollmeyer, a well respected trout fishing authority, author, and lecturer. Without attempting to discredit Jim, I suspect that Jim's understanding of entomology was largely based on knowledge imparted by his friend Dr. Richard Hafele, a specialist in entomology. Jim's stream experience has undoubtedly confirmed his understanding of aquatic insects.

The article appearing in the McCloud Preserve Newsletter specifically states that with regard to heptageniids "that metamorphosis from nymph to subimago takes place underwater rather than at the water-air interface like so many other mayflies". The article implies that flatheads are a distinct group within the clinger family that can exhibit this behavior. The article further states that the genera Rhithrogena and Epeorus are the most notable flatheads appearing within the Preserve. Cinygmula also appear there.

In Schollmeyer's discussion of the Epeorus mayfly, he states that Yellow Quills "leave their nymphal shucks while still under water, either at the bottom or close to the surface". In his discussions of other western Heptageniidae he simply stated that the nymphs crawl to calmer water before emerging. There the nymphs quickly swim to surface where the duns waste no time emerging. There may be a tacit assumption here that they could really emerge from just below the surface since they take flight so rapidly.

These two references agree and confirm that at least one flathead emerges (Epeorus) from the water column as a dun. Your research suggests that Heptagenia are also capable of emerging in the same way. I further checked with Dr. Hafele to determine whether the heptageniids as a family practiced this type of emergence. He indicated that some species among the genera in this family emerge beneath the surface. In particular, certain species within the Epeorus (Yellow Quills), Heptagenia (PEDs), Rhithrogena (Western March Browns), and Cinygmula (Blue Wing Red Quill) genera exhibit this behavior. He interestingly indicated that this behavior is not unique to species within the Heptageniidae family. Genera in other families also exhibiting this emergence behavior included the Mahogany Dun (Paraleptophebia), the Green Drake (Drunella grandis), and the PMDs (Ephermerella ). He cites a technical article by Edmonds and Berner to support this position.

I regard these findings important to fly fishers because they imply an approach to fishing with heptageniid patterns. First, routinely fishing with heptageniid nymphal patterns will be largely futile.. These invertebrates are so effective at clinging to the bottoms of rocks that they simply are not available to trout in the water column except during a hatch. Second, nymphal patterns will be suitable for use just as a hatch begins because the nymphs release themselves from the rocks. Third, wet hackle and weighted dun patterns can be effective as the hatch progresses. These patterns would simulate an emerging nymph and a dun, respectively. This technique is advised for use on the McCloud River in California during their March Brown and Yellow Quill hatches. I would conjecture that trailing a nymph might be doubly effective.

I hope that this additional information will be helpful to your readers.

John Claassen

If you have a question, please feel free to contact me.
~ C. E. (Bert) Cushing, aka Streamdoctor
105 W. Cherokee Dr.
Estes Park, CO 80517
Phone: 970-577-1584

The 'Stream Doctor' is a retired professional stream ecologist and author, now living in the West and spending way too much time fly-fishing. You are invited to submit questions relating to anything stream related directly to him for use in this Q & A Feature at

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