Ladyfisher called my attention to a very
interesting dialogue in the FAOL Bulletin
Board pertaining to a "almost hatch" phenomena
and the resulting exchange on mayfly taxonomy.
She has asked me for my comments.
First, I can't comment knowingly on the "almost
hatch" phenomena. It could well be related to
one of the types of drift phenomena, but the
brief description precludes anything definitive.
Second, I do have some comments on the related
taxonomical discussion. To start, I want to
emphasize that the following comments are not
meant to sound elitist nor in any way denigrate
the comments/opinions of those who participated
in the exchange. I firmly believe that much can
be learned from dedicated non-professionals and
the pros can learn much from them. Having said
that, however, I think some cautionary comments
The contributors to the bulletin board dialogue
spent a lot of time discussing the identification
of nymphs to species. The fact of the matter is
that even the pros are reluctant to do this except
in certain cases. For instance, if you have a
baetid nymph with two tails, it's a pretty good
bet that it is Baetis bicaudatus.
However, most specific identifications are based
on patterns of wing veination, structure of
reproductive organs, and other characteristics
that manifest themselves in adults, but not
immatures. Taxonomists typically raise nymphs
under laboratory conditions to collect the adults
and thus match them with known nymphs. Even then,
they hesitate identifying immatures to the species
level in the field because of (1) inherent variations
in color and other characteristics that can be
influenced by habitat conditions, and (2) the
lack of distinctive morphological characteristics
in immatures. The latter makes field identification
of immatures to species particularly difficult when
more than one species of the same genus is present.
I know of streams where there are several species
of Ephemerella present; it would be
risky to try to put specific names on these unless
(1) they were quite distinctive morphologically from
the others, and (2) you had confirmative information
from adult identifications.
To pursue this a bit further, let's look at the genus
Ephemerella, the genus addressed in the
bulletin board dialogue. The family Ephemerellidae
contains 90 species within its 7 genera, and the genus
Ephemerella contains 47 of these. All
are morphologically similar, to some degree, and the
other 6 genera have only recently been separated from
Ephemerella. So, can a person distinguish
which of the 47 species he finds? Some species, of
course, can be eliminated because of distributional
ranges, but some ranges overlap. What I'm trying to
point out here is that it is extremely risky to put
specific names on immatures unless you have a
pretty damned good knowledge of what has been identified
from the stream as adults.
Ecologists are sometimes successful in naming
immatures to the species level when they have a
limited number of species of the same genera
present in their study site and they are
able to collect adults for positive specific
identification. In this case, it is reasonably
safe to then put a specific name on the nymphs.
I guess this is why those of us with scientific
backgrounds in this area and who are also fly
anglers tend to be rather skeptical when we see
specific names published in the popular literature.
For instance, many streams have several species of
Baetis present that even a taxonomist
would hesitate in identifying to species as nymphs;
yet the fishing literature is full of names to the
specific level. I can't say they're wrong; it's
only that I get skeptical when knowing how difficult
it is to identify insects to the species level. Another
example: Baetis and Callibaetis
can be found in the same environment in places and the
main morphological difference that separates the two
genera are that the gills on Callibaetis
have a small flap that can only be seen under a dissecting
microscope! Adults are quite similar, yet writers don't
hesitate in giving scientific names to the hatch they're
fishing. I know some taxonomists who have confided that
they wish they had as good an eye as some angler writers!
I'm very impressed by the knowledge and interest shown
by all of you and certainly encourage your efforts.
I guess a career as a scientist and the need for
showing proof of what I say instilled a healthy dose
of skepticism in my personality. So be it.
If you have a question, please feel free to contact me.
~ C. E. (Bert) Cushing, aka Streamdoctor
105 W. Cherokee Dr.
Estes Park, CO 80517
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