Insects and other foods the trout may be eating:
1. Blue-winged Olives
2 . Sculpin, baitfish and small crayfish (Imitate with streamers)
3. Great Autumn Brown Caddisfly
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Part Five - Subimago Mayflies
New Great Smoky Mountains National Park Trout Food Series
Now I can just see some of you frowning, thinking "what the ____is a subimago"? I'll
explain in just a split.
So far, we have covered the larvae stage of life of the four types of common aquatic
insects found in the park. We have also covered the pupae stage of life for the
caddisflies and midges that undergo full metamorphosis. Now we will get into the
fully grown stage of life of these four, main aquatic insects, starting with mayflies.
A mayfly is different from many other aquatic insects in respect to the way it
matures. Once the larva (nymph) reach maturity, it transforms into what scientist call
a "Subimago" or what anglers call a "Dun". This process is usually called the
"hatch". To a new guy, just starting to learn about aquatic insects, it makes more
sense that the "hatch" is when the eggs hatch into nymphs. However, that's not
consistent with typical angler terminology. The "hatch" occurs when the nymphs
change into a dun. I guess you could say they "hatch" out of the water instead of
hatch out of an egg.
It's during the "hatch" that mayflies are very likely to become trout food. Depending
on the species of mayfly, the larvae can swim, drift in the current or crawl to the
surface of the water to molt (hatch). They can also crawl out of the water to molt, or
even molt underwater - requiring the dun to have to swim to the surface. Quill
Gordon mayflies molt this way - underwater. Most mayfly nymphs swim to the
surface to hatch. Only a few crawl out of the water to molt. The Slate Drake is a
mayfly that molts out of the water. Irregardless of which method they use to molt,
during the molting process, the mayflies become very vulnerable to predators,
mainly trout. This "hatch", or "emergence", or "molting process", whatever you want
to call it, takes anywhere from a few seconds to a few minutes for the wings to clear
the wing cases of the larvae and dry to the point the insect can fly. Instead of the
phase "sitting ducks", I guess you could say mayflies are "sitting mayflies" during
this time. Trout can easily pick them off.
The appearance of the insects, starting out as a nymph and ending up as a fly with
wings, undergoes a huge physical transition. In fact, the insect looks almost
completely different every few seconds, so to speak. At one point it looks more like
a pregnant nymph than a fly due to the expanded wing pads..A few seconds later,
after the wing pads open, it looks more like a fly with collapsed wings than it does a
nymph. We imitate this look with an plain emerger pattern. Yet a few seconds later,
it looks like a nymph with a translucent shuck or skin attached to its tail. Anglers
imitate this look with what's called a emerger fly pattern with a trailing shuck. Finally,
it becomes a subimago with fully upright wings, ready to fly away. Anglers call this a
dun and imitate it with a dun fly pattern. The dun usually only sits or drifts on the
water (assuming it hatches on the surface of the water) for a very few seconds,
depending on many variables and especially the water temperature and weather
Next, comes the part of a mayfly hatch that's different from other aquatic
insects. The mayfly is called a "Sub" imago because it hasn't yet reached maturity.
They normally remain a subimago or dun, for a day or two, but the time depends on
the species and weather. It is only a few minutes in some cases for certain species.
During this time the wings generally become translucent and the males eyes, legs
and genitalia continue to fully develop. The tails and legs become much longer. The
Dun, or subimago, changes into what scientist call an "Imago" and anglers call a
"spinner". If you want to use the "adult" terminology, then a mayfly becomes an adult
when it becomes an imago, or a spinner.
These spinners only live for a short time. They cannot eat. Their behavior is strictly
oriented towards mating and oviposition (fancy word for egg laying). This
reproductive behavior gets them swarming and in some cases, into upstream flights.
The swarming mayflies are usually males. There are a few exceptions but it is
usually males flying up and down out over the water. When a female joins the
swarming males, she is caught from below by a male and mating takes place during
the flight. This activity usually takes place late in the afternoons, early evenings or
in some cases, early mornings. When the male finishes mating, he falls dead,
usually on the water.
The female spinner lays her eggs three different ways. Some drop them when they
are flying low above the water; others touch the water and knock the eggs off or
either just land on the water and deposit them; and others dive into the water and
deposit them on underwater objects. When the females finish, they usually end up
on the water in most cases. When they die, both the males and the females get into
what anglers call the spent position with their wings floating flat on the water, not
any longer in an upright position. These are called "spent spinners". Trout can feed
on them with ease. In fact, this is the easiest meal a trout ever gets. Their prey
cannot escape. They usually just gently sip the spinners from the surface and about
all the angler can see, if there is enough light, is the fish itself or a rise ring. Most of
the time, the rise ring is the only indication of a trout eating a spinner. The spent
mayflies soon drift off and get caught up in eddies or along the banks or objects
such as rocks that extend out of the water. They will soon sink. The trout will
continue to eat them even after they start sinking. Trout are not the only thing that
eats the spinners. Birds, dragonflies, damselflies, spiders, and even biting midges
Aren't humans lucky. Most of the time, not always, but most of the time, they have
sex and continue to live. Mayflies don't have that option.
Copyright 2010 James Marsh
Although experienced fly fishers may know several or
even most all of the tips included in the "Top 85 Tips on
Fly Fishing" program, any one of them could prove to be
well worth their time and money invested in viewing this
program. Being reminded of some of the ones they may
be guilty of overlooking could also be of value. The
program applies to the entire spectrum of fly-fishing for
trout including tips on gear, methods, techniques,
approaches, strategies and many other elements of the
sport. The program is introduced and concluded on
Montana's Blackfoot River, home to the movie "A River
Runs Through It".
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