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Lateral view of a Male Baetis (Baetidae) (Blue-Winged Olive) Mayfly Dun from Mystery Creek #43 in New York
Blue-winged Olives

Tiny Baetis mayflies are perhaps the most commonly encountered and imitated by anglers on all American trout streams due to their great abundance, widespread distribution, and trout-friendly emergence habits.

Dorsal view of a Holocentropus (Polycentropodidae) Caddisfly Larva from the Yakima River in Washington
This one seems to tentatively key to Holocentropus, although I can't make out the anal spines in Couplet 7 of the Key to Genera of Polycentropodidae Larvae nor the dark bands in Couplet 4 of the Key to Genera of Polycentropodidae Larvae, making me wonder if I went wrong somewhere in keying it out. I don't see where that could have happened, though. It might also be that it's a very immature larva and doesn't possess all the identifying characteristics in the key yet. If Holocentropus is correct, then Holocentropus flavus and Holocentropus interruptus are the two likely possibilities based on range, but I was not able to find a description of their larvae.
27" brown trout, my largest ever. It was the sub-dominant fish in its pool. After this, I hooked the bigger one, but I couldn't land it.
Troutnut is a project started in 2003 by salmonid ecologist Jason "Troutnut" Neuswanger to help anglers and fly tyers unabashedly embrace the entomological side of the sport. Learn more about Troutnut or support the project for an enhanced experience here.

This topic is about the Mayfly Species Ephoron leukon

See the main Ephoron page for details about this species, which is not known to differ in any important ways (besides location) from the other species.

On page 243 of Hatches II there is a passage from an 1802 speech before the American Philosophical Society in which this mayfly was introduced to science. It was the first mayfly species described in the United States, so it is ironic that it went unnoticed through so many of the early decades of our sport.
Posts: 2
BFornadley on Feb 8, 2007February 8th, 2007, 3:29 am EST
I need some help here. I have been looking all over the web for someone who may have taken some Ephoron Leukon nymph underwater (or out of water) photos.I saw the description here at "Troutnut.com" and advice that a smaller Brown Drake (Ephemera) nymph would be a good natural to use as a tying model but I really want to see the real thing. Does any body have any of these pics or can anyone definitively tell me where to look?
May you always keep your powder, martinis and flies dry !
Taxon's profile picture
Site Editor
Plano, TX

Posts: 1311
Taxon on Feb 8, 2007February 8th, 2007, 12:26 pm EST

Mayflies by Knopp/Cormier (on page 125) has three excellent black and white drawings, a dorsal view of a mature Ephoron leukon nymph, an anterolateral view of its head, and a dorsal view of its gill structure.

Mayflies by Fauceglia (on page 188) has an beautiful (dorsal view) color photo of a mature Ephoron leukon nymph.

If you were to contact me via my website, perhaps I could further assist you.
Best regards,
Roger Rohrbeck
Troutnut's profile picture
Bellevue, WA

Posts: 2758
Troutnut on Feb 11, 2007February 11th, 2007, 8:07 am EST
I'm afraid I don't have any Ephoron nymph pictures. I'm not sure I'll be able to get any this year -- maybe if the hatch starts early in the Delaware system. I've tried to catch them in the past but for some reason I couldn't get any to turn up in a kick net sample, even in rivers with high populations.
Jason Neuswanger, Ph.D.
Troutnut and salmonid ecologist
Site Editor
"Bear Swamp," PA

Posts: 1681
GONZO on Feb 12, 2007February 12th, 2007, 6:07 am EST

In addition to the references that Taxon mentioned, there is also a nice picture of an Ephoron nymph in Thomas Ames' Hatch Guide for New England Streams. What is missing when you view dorsal photographs of these nymphs, however, is that the thorax of the mature nymph often has a distinct pinkish-orange coloration. Many anglers who fish the famous "white fly" hatches on the Yellow Breeches consider this to be an important and attractive trait to imitate.
Troutnut's profile picture
Bellevue, WA

Posts: 2758
Troutnut on Feb 12, 2007February 12th, 2007, 8:34 am EST
I know they're burrowers. I've turned up plenty of small burrower nymphs in my search, but they all turned out to be immature Hexagenia or Ephemera. I'll just have to keep looking.
Jason Neuswanger, Ph.D.
Troutnut and salmonid ecologist
Posts: 2
BFornadley on Feb 12, 2007February 12th, 2007, 12:30 pm EST
To Everyone who commented on my question concerning Ephoron Leukon Nymph Photos - Thank you all so very much- already I have what I need - it is so great to have good knowledgeable help at my fingertips and I wont forget it - I am at the ready to help all of you. Talk to me on things like great bamboo rods /makers- nymph fishing in general, exotic travel on the cheap and my personal favorite- Lake Erie feeder stream steelhead fly fishing
May you always keep your powder, martinis and flies dry !
Bolivar, MO

Posts: 14
Sirhoops23 on Feb 13, 2007February 13th, 2007, 2:26 am EST
I would love to hear advice on nymph fishing from you. Just good tactics, drifts, waters etc. I came from Colorado where I did a lot of dry fly fishing and could use all the help I can get on nymphing.
Posts: 1
Riverhead on Jul 30, 2007July 30th, 2007, 1:01 pm EDT
Here's a link to a nymph pic that I just found while preparing for the upcoming hatch.

Wiflyfisher's profile picture

Posts: 622
Wiflyfisher on Aug 2, 2007August 2nd, 2007, 9:11 am EDT
Okay, over the next few evenings I am going to try to put down my rod (ha!!) and get some Ephoron luekon (or album) duns, emergers and nymphs on my favorite Midwest river. We had a major cool front come through last night so hopefully the fish and white bugs will cooperate.

I have a small mesh, bug seine and I plan on taking some ice in a cooler to hopefully delay the bugs transitioning from one stage to another. Any thoughts or tips for collecting and shooting photos of this elusive nighttime flyers?

So far I have captured Ephoron luekon duns and spinners (no nymphs):

See: http://www.wiflyfisher.com/ephoron-leukon-mayfly-hatch.asp
Posts: 107
Gene on Aug 14, 2007August 14th, 2007, 9:58 am EDT

You are welcome to use the photograph of an emerging Ephoron nymph from the Yellow Breeches from my website; www.limestoner.com; just don't abuse it; here's the actual page link:


If you tie a pattern similar and fish it in the film and as emerger I believe on most streams you will be rewarded. The fly fishes much better than dun patterns which are not that effective on most streams

tight lines...rising trout

gene macri
Wiflyfisher's profile picture

Posts: 622
Wiflyfisher on Aug 14, 2007August 14th, 2007, 10:56 am EDT
Gene, may I post you E. leukon nymph photo on my web page dedicated to Ephoron leukon? I would include a link to your web site with full credit.


In all my years fishing this hatch in the Upper Midwest on a great trout stream I have never caught the elusive nymph. Thank you!

BTW, I am finding the hatch seems to be occurring later in the evening then it use too 20-25 years ago on my favorite freestone trout river. And it's not because the water temps are warmer on this river. This may be coincidence since I have no scientific data to back it up, just my observations.

Posts: 107
Gene on Aug 14, 2007August 14th, 2007, 3:46 pm EDT
Sure go ahead and post it and thanks for the link.

tight lines and rising trout


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