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The Specimen

Ephemerella subvaria (Hendrickson) Mayfly NymphEphemerella subvaria (Hendrickson) Mayfly Nymph View 2 PicturesI've never seen this strange coloration on any Ephemerella subvaria nymph in a book before, but it's similar to several other specimens I collected on the same outing, including a larger one that I photographed. They were outnumbered by the "normal" Ephemerella subvaria nymphs in the sample.
Collected March 29, 2005 from Salmon Creek in New York
Added to Troutnut.com by on April 7, 2006

The Discussion

BrookymanMarch 8th, 2013, 12:36 am
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Posts: 797
Why is it on some of the subvaria the pronotum is clear or whitish. Is that part of the
molting process on them ??? And why does it not happen on other Ephemerella's ???


Mack.
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EntomanMarch 8th, 2013, 1:32 am
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Northern CA & ID

Posts: 2604
Good question, Mack. It's one I've asked myself and I'm not sure there is an answer (yet). I believe there are several hypothosis that pose causes from water chemistry, diet, to substrate camouflage adaption. What none of them seem to explain is why only some of the population will appear this way. Like the occasional bright red heptageniid, there are probably genetic reasons for these, I would think.

What I do know is this color pattern has nothing to do with molting and is not limited to subvaria. It is fairly common in several ephemerellid populations, particularly in those streams where the substrate largely consists of clean granitic cobble that makes a good case for camouflage. The real interesting ones are those that live in less sterile environments, often in clumps of green weed. I generally see this most dramatically demonstrated in the Drunella genus, where some can even be dark olive or chocolate all over except for a pale cream pronotum. Check these out.
http://www.laughingrivers.com/images2/drunellanymph-200x.jpg
http://bugguide.net/node/view/569052
http://bugguide.net/node/view/620404
"It's not that I find fishing so important, it's just that I find all other endeavors of Man equally unimportant... And not nearly as much fun!" Robert Traver, Anatomy of a Fisherman
BrookymanMarch 8th, 2013, 1:46 am
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Posts: 797
Wow that's wild The camouflage theory looks very good on those ones. Does it happen on invaria as well just wondering if some of the ones I see are that and not subvaria.

Mack.
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EntomanMarch 8th, 2013, 1:53 am
Site Editor
Northern CA & ID

Posts: 2604
Sure. I've seen this character from time to time in lots of different ephemerellids. The last photo I linked seems to be a camo adaption because this type shows largely population wide in some streams. Those two toned jobs seem to represent a small fraction of any given population, suggesting a different reason for their appearance.
"It's not that I find fishing so important, it's just that I find all other endeavors of Man equally unimportant... And not nearly as much fun!" Robert Traver, Anatomy of a Fisherman
BrookymanMarch 8th, 2013, 2:55 am
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Posts: 797
Cool I will look for some this spring. I can't believe its snowing again :)
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