01/14/10

Basics of Fly Fishing - Trout Food Series - Mayflies - Part 3
The mayflies that exist in the streams of Great Smoky Mountains National Park are
mostly clingers. There are also several species of swimming mayfly nymphs but
relatively few crawlers and very few burrowers. The fast water of the mountain
freestone streams are a much better habitat for the clinger nymphs than the other
three types of mayfly nymphs. Most all of the stonefly nymphs are also clinger
nymphs. The swimmers can find plenty of places to get out of the fast water. All of
the streams have pools and some small areas of calm and slower moving water.
Even in the fast water, the swimming nymphs can find plenty of places out of the
direct current to avoid it. Even so, there are still fewer swimming nymphs than you
would find in most moderate to slow water trout streams.

If you have ever tried to pick up a clinger nymphs from a rock, you would
understand why they can survive in fast water.  Most of the time you will find them
under the rock, not exposed on top of them. When you try to pick one up, you will
find that you have to pry its flat, clinging body from the rock. It is streamlined in such
a way that the water flows over it's body. A round shaped crawler nymph cannot
handle the fast water near as well. The swimmers dart through it but mostly just
avoid it. The burrowers want be found in it at all. They prefer a slow water with a
soft bottom where they can live in their burrows. There's little habit suitable for them
in the Smokies.

These four types of mayfly nymphs don't resemble each other very much at all.
They each have 6 legs, a head, body and thorax and two or three tails but that is
about the extent of their resemblance. The clingers, which again are the most
plentiful mayflies in the Smokies, have long legs that can grip the rocks, and flat
heads, abdomens and bodies that offer little resistance to the current. You cannot
really tell the thickness of the nymph from the image, but it is shaped very flat. Look
at the size of its legs. They help it grip the bottom. When it isn't crawling around on
the bottom feeding, it is hidden down between and under the rocks on the bottom of
the stream in the faster current in highly oxygenated water. Notice its gills are
relatively small compared to many mayfly nymphs. It must have lots of oxygen in the
water to obtain the amount it needs. Notice the eyes on top of its head, not the side.






The swimmer nymphs, consisting mostly of Blue-winged Olives and larger Slate
Drakes in the Smokies, sometimes locally incorrectly called Mahogany Duns
(Isonychia bicolor) have longer, skinny, streamlined bodies. The Slate Drake nymph
shown below is so round it want even lay on its stomach. It rolls over on its side
because its legs tend to extend downward, not out to its sides. They can be folded
up out of the way when it swims. They look more like little minnows in the water than
mayfly nymphs. They swim much like miniature otters. Their gills are stung out
along the entire length of their bodies and they can live in a variety of different
types of water with only moderate amount of dissolved oxygen.


                                                           



The crawler nymphs, which are not very plentiful in the Smokies, can adapt to a
large variety of types of water. Notice they have larger gills, short legs and tails.
This particular one is an Eastern Blue-winged Olive. That common name is
misleading because it isn't a swimming nymph like most all other BWOs. It is a
crawler nymph and a member of the Drunella family of mayflies. In fact, it's in the
same family as a Western Green Drake, it is just a small version. Its big front legs
makes it easy to identify. If this mayfly nymph gets caught in fast water, it will be
send tumbling down the stream trying to catch hold of something. It cannot swim.
This one was found in calm water near the end of a pool in Little River near
Elkmont. There are few of them in the park. Most of the Sulphurs and Eastern Pale
Evening Duns are crawlers. The Hendricksons are crawler nymphs. The prefer slow
to moderately flowing water. Their gills are large enough to get oxygen from that
type of water. That is why there are few of them in the Smokies and when you do
find them, they are in moderate to slower moving water in isolated areas of the
streams. Notice their eyes are on the sides, unlike the flat clingers.





Not only do these three types of nymphs look different, especially if you could hold
one in your hand and see the difference in the shapes of them, they behave
entirely different.

The crawlers do just that - crawl along the bottom in moderate water. They hold on
as best they can but stay out of the fast current. They hide behind what ever they
can find. Leaves, sticks, rocks, and normally, vegetation which there is little of in the
Smokies. You will find more of these in the marginal areas of the fast water and in
the pools.

The clingers are found in the fast water of the runs and riffles but alway under the
rocks or down in between them. They can hold on in the fast current. These are the
March Browns, Quill Gordons, Cahills and Little Yellow Quills. They are the most
plentiful mayflies found in the Smokies because most of the water is fast, pocket
water that provides the perfect habitat for them. Although they are plentiful, keep in
mind that they only time they are really exposed to the trout is part of the time they
are feeding or they are getting ready to hatch.

The swimmers are found in the marginal areas of the fast water, in pockets of slow
to moderate water and the pools. The do what their name implies. They swim but do
so it short, darting motions and in comparison to fish, swim rather poorly. Mostly
Slate Drakes and Blue-winged Olives, consisting of several varieties including the
baetis species you often hear about, but there are others. Although there are a lot
of species, none of them are found in very large quantities because only part of the
streams in the Smokies provide the type of habitat they prefer.

The burrowers are not common at all in the Smokies. The largest  of them, the
Eastern Green Drakes are found mostly in Abrams Creek. There are also some
huge Great Olive Winged Duns, called Hexs in Michigan, found in the warmer
sections of some of the streams such as Little River where the slightly warmer water
is marginal for trout. We have also found some Brown Drakes and Yellow Drakes in
some of the streams where there is a soft bottom suitable for the burrows they live
in as nymphs but mostly outside the park boundaries. Except in these isolated
areas, you would do best just to forget burrowing mayflies in the Smokies.

I hope you are beginning to see a nymph isn't just a nymph. They resemble
each other about as much as a bear resembles a billy goat. More importantly, they
don't live together, eat or behave the same way. You should have also noticed from
reading yesterday's article that trout eat far more mayfly nymphs than duns - my off
hand guess would be maybe 100 or a 1000 times more.

How many Quill Gordon nymphs do you have in your fly box? How many Blue Quill
nymphs do you have? Both of them will hatch in another month or two. Oh, and by
the way, how is your stock of Light Cahill nymphs? When you ask for them at your
local fly shop, don't be surprised if you either get a dumb look or a dumb answer.
Either way, I feel sure you will leave with some hooks with some hair tied on them
that are "supposed to work just fine".
Click on image to expand the size and
see the detail I want you to see.
Click on image to expand the size and
see the detail I want you to see.
Click on image to expand the size and
see the detail I want you to see.