1. Troutnut Forum
›
2. Fly Fishing
›
3. Ephemerella dorothea nymphs

I just returned from a ten day trip to the Beaverhead and a few other SW Montana streams. I'm hoping some of the really knowlegeable bug men here can explain something to me. When I did some investigation of the nypmh life in the stream we fished most of the aquatic vegetation was full of light olive green nymphs that appeared to be Ep dorothea aka Ep infrequens for those older fly guys like me who don't keep up with the name changes.

The nymphs I collected were slender and no longer then 12 mm. They were uniformly the same color green and appeared to have gills along the abdomen. Now the query ---when the nymphs started to drift, and the duns began emerging the shucks were totally black. Do the nymphs change color, from olive green to black just prior to emergence?

By the way the fishing was very good and if I can figure out how to reduce the size of my pictures I'll post some of them here. Thanks in advance!

Hi,
Could it be because the exoskeleton on the nymph is dark that once empty it appears black? The fly is comparatively lighter than the nymphs, meaning the internal fly is lighter,and shows through the darker covering? This is what I'm thinking, anyway.

Mark

Wbranch, can you recall whether any of the olive green nymphs you saw in the aquatic vegetation had black (or darkened) wingpads?

Sounds like you found some Ephemerella excrucians (was inermis). I reared some of the nymphs to the spinner stage a few years ago from that area.

They do kind of change color.

I've always thought enermis was much smaller than dorothea??? Swisher and Richards "Selective Trout" indicate the size to be 5.5 mm - 7 mm or a #20 - #22 hook. The live nymphs and the empty shucks were in the 10 mm - 12 mm range. I collected more than one on the tip of my index finger and they are not olive at all (like the live nymph) but very dark - dark gray to black. I guess I'll just have to wait unti next year and collect a few live nymphs and empty shucks and post some pictures here so you guys can see the actual specimens. Thanks anyway.

Here is a pretty good representation of the browns we were catching.

Stunning fish, Wbranch. I'd say that a trip back to the Beaverhead is essential--strictly for taxonomic clarification, you understand. At least, that would be my story, and I'd stick to it. ;)

Holy crap, Wbranch! No wonder you had to reduce the size of the pictures before you uploaded them! What a fish!

-Shawn

Thanks guys!, yes it was a lovely male a bit more than 22". It ate a #18 PMD with medium dun CDC wings and a yellow grizzly hackle. My friend took a few other pictures that better portray the full depth of this fish and I'll post them when he sends me the file. I agree another scientific trip is necessary to capture some nymph specimens but I'm not sure that my wife will understand that I wouldn't ask to go if it wasn't for the advancement of entomological research!

Great fish! We're awaiting your next scientific excursion. It should be interesting.

Mark

inermis and infrequens (=excrucians and =dorothea infrequens) can live in the same stream, with infrequens in the higher gradient areas and inermis usually in the slower, flatter places, often in with the filamentous algae. there still are a lot of questions about the IDs of Ephemerella spp., especially in places like SW Montana, so you will just have to keep going back until all the entomologists agree on the answer. ;)

Konchu,

"especially in places like SW Montana, so you will just have to keep going back until all the entomologists agree on the answer. ;)"

Okay, that sounds like a fine plan to me!

The picture of the large brown was my largest fish of the trip here is a picture of the average we caught. While I didn't measure it it appears to be in the 18" - 19" range.