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September 15th, 2003
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My recent column on whether or not mayflies emerge under water has generated some interesting responses:
Q.
From Alan Shepherd: It would seem that a few rare
species of mayfly actually do emerge as a dun underwater.
To my way of thinking, if it actually happens, the angler
will not know anyhow. The take home information is that
duns can be fished underwater as well as on the surface,
trout don't study entomology!
Mr. Shepherd submits the following extract from an article
by John Claassen published on the New Mexico Trout website:
"An interesting aspect of the emergence is that the
metamorphosis from nymph to subimago (dun) takes place
entirely underwater rather than in the water-air interface
as it does with so many other mayflies. This means that
they transform directly from a nymph to a dun while at
depth. The nymphal shuck is removed in the process.
Either during the transformation or after the transformation,
the flathead/clinger (his name for this group of mayflies)
normally drifts for a long distance before reaching the
surface. This gives the trout plenty of time to feed on
them, perhaps without even breaking the surface. This
implies that dun patterns can be fished successfully wet
as well as dry during an emergence.
To read the entire article, go to:
www.newmexicotrout.org/Pro_Tips/ProTips_Flathead%20Mayflies.htm
From Matt Pierce: I thought I read about the bi-colors
being the only mayfly to emerge under water. I believe
it was in Selective Trout. I think I
could have been wrong though. I know they can't inflate
their wings but everything is supposed be ready by the
time they get to the top. Please let me know what you
find out.
From aacfish: (partial text) Thank you for your reply
to my question on underwater mayfly emergence. So far,
I have not been able to find anything that confirms
total underwater wing extension. Check under Epeorus
under entomology in westfly.com.
A.
To Alan Shepherd: Thanks for your input. It brings
up several interesting points. First of all, I do not
know John Claassen or his credentials on the subject.
Of interest, however, is the fact that there is a genus
of stoneflies (Plecoptera) with the name of
Claassenia. The name was coined by a
man named Wu to honor P.W. Claassen, an early taxonomist.
With such an unusual name, it would not be surprising
if there was some connection. Anyway, back to the article.
Mr. Claassen's article is entitled "Mayfles in the
Heptageniidae Family Live in the Fast Lane." and
concerns only the single family. He mentions several
genera in this family and then makes the quote shown
above concerning metamorphosis from nymph to subimago;
it gives the impression that the quote applies to all
genera in this family.
So, what can we deduce from this? Although Mr. Claassen
seems to broadly infer that all Heptageniidae are subsurface
emergers, it appears that only two genera, Epeorus
and Heptagenia, sometimes emerge under water,
and that this appears to be the exception rather than the
rule. Remember, too, that there are 19 species of Epeorus
and 13 species of Heptagenia. Edmunds et al.
were presenting generic characteristics and we cannot be
sure how many of these 32 species exhibit underwater
emergence.
To Matt Pierce: I must admit that I'm not sure what
you mean by "bi-colors," nor do I have a copy of
Selective Trout. Thus, I hope this
column satisfies your interest.
To aacfish: Thanks for the additional information.
Whoever wrote the section on Epeorus
implies that all species in this genus emerge underwater.
Edmonds et al. seem to hedge the bet a bit and, in fact,
imply that surface emergence is more likely.
Summary: How does this fit with my earlier column?
The experts I talked to (4 universities, 1 state
department of natural resources) and four of the
books I consulted provided no support for subsurface
emergence by mayflies. Only upon digging into the
generic details in the Edmunds et al. book, did I
find mention of two genera that occasionally emerge
underwater. Additional information from the
westfly.com website lends credence, though painted
with a broad brush.
I suspect an appropriate, generalized statement as
to mayflies emerging underwater might read something
like: Mayflies, in general, do not emerge underwater;
however, there is some evidence of underwater emergence
in two genera of the family Heptageniidae.
My apologies for misleading anyone in my earlier column.
Seems like we never stop learning.
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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
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