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Topic: Mayfly - Ephemerella excrucians - nymph
EntomanNov 14, 2011 23:02 0132-0001

Northern California

Topics started: 55
Replies made:  783


Can you help with I.D.?

Location: Fall River, CA
Date: November 12, 2011
Habitat: Weedy slow run
Size: 10 mm.
Specimen status in photo: Live
Collection method: D-net swished through weeds

Entoman
TaxonNov 15, 2011 01:01 0132-0002

WA, USA

Topics started: 127
Replies made:  623
Kurt-

I believe it to be Ephemerella tibialis. What are you thinking?


Roger Rohrbeck
EntomanNov 15, 2011 17:54 0132-0003

Northern California

Topics started: 55
Replies made:  783
Hi Roger,

Well, I don't know what to think. I agree with you that it sure looks like tibialis. The photo isn't sharp enough to rule out small rounded dorsal tubercles and the tails are pretty banded and don't look hairy enough distally to be infrequens or excrucians. The problem is it's way too big for tibialis.

I've never looked at this critter with this kind of magnification before and always assumed it was just a dark phase of infrequens due to its size. I'm fairly confident that this is the nymphal stage of the olive-green dun I posted a few weeks ago. I must admit the color and prominent lateral spikes on the dun have always puzzled me. Perhaps we're looking at something different? Fall River is an unusual fishery. Do you think Luke might be interested? I have both preserved...

Regards,

Kurt
Entoman
EntomanDec 15, 2011 23:06 0132-0004

Northern California

Topics started: 55
Replies made:  783
Hi Roger -

Thanks for the help in contacting an entomologist.

After inspecting the specimen, it seems the best that biologists can do with any certainty at this point is classify this specimen as a strain of Ephemerella in the PMD category. It's not tibialis as we suspected over lack of terga tubercles. E. d. infrequens is as sure a bet as any, so that's where I'll place it until better information becomes available. Why not leave it at the genus level? Because this specimen is as assuredly infrequens as any other specimen of infrequens is at this point. If this sounds murky, it's because it is.

Regards,

Kurt


Entoman
EntomanFeb 12, 2013 01:16 0132-0005

Northern California

Topics started: 55
Replies made:  783
Roger -

Well, the latest info that seems to be reliable is that the tips of the claws curve in sharply with excrucians while the curve is more uniform with infrequens. This specimen clearly shows the former. Coupled with the date of emergence, that is probably where it needs to moved for now. Konchu raised the real possibility that it could eventually be found to be something else, but for now those are the two species of PMD's recognized.
Entoman


Created: 01/12/2010   Last modified: 12/26/2014    www.FlyfishingEntomology.com