|.............................Fly Fishing Yellowstone National Park
Probably most of you can tell one type of bug from another but for those who
can’t, or are just getting started fly fishing, let me briefly cover some basics of
An aquatic insect is one that is born and lives most of its life in the water. A
terrestrial insect is one that is born on land and spends all of
its life on land, unless it accidentally falls or is blown into the water.
Mayflies, caddisflies, stoneflies and midges are aquatic insects. Grasshoppers,
ants, crickets and such are terrestrial insects. There are others that fit into these
categories, damselflies, dragonflies, crane flies, and so forth, but for the most
part, this represents the bugs trout eat. Trout Bugs 101 is being able to tell a
caddisfly from a mayfly from a stonefly from a midge.
Mayfly nymphs have either two or three tails. They can be easily confused with
stonefly nymphs. If you are not sure, check their legs. Mayfly legs end with a
single claw and stonefly nymphs with two claws. Plate like gills are present along
the abdomen of a mayfly.
Stonefly nymphs have two short tails. Their legs end with two claws. They either
have no visible gills or their gills are found under their head or upper body.
A Caddisfly larva looks like a little worm or if it is a cased caddis, a little worm in a
case with its head and maybe its tail stuck out. They are very easy to distinguish
from a mayfly or stonefly nymph.
A Midge larva is a tiny, worm looking creature that is usually burrowed in the soft
bottom of the stream or lake. They can be confused with an uncased caddisfly
larva, but for the most part, are much smaller. Now lets look at the adult flies.
Mayfly adults look like little sailboats on the water. The have two, larger upright
wings and can and usually do have two little ones called hind wings.
Adult stoneflies have (4) four wings but they are folded flat on top of the fly and
look like one wing when they are at rest. In the air, they look larger than they
Adult caddisflies also have (4) four wings but they are folded in a tent shape
when the fly is at rest. They two look much larger in the air than they really are.
Midges are tiny (2) two winged flies that look like mosquitoes. Much of the time
they are difficult to see in the air or on the water. Don’t just assume the small
flies you see are midges. They may be mayflies. Take a closer look.
You should learn to be able to recognize these (4) four different types of flies as
a nymph or larva, as a pupa (if this stage of life exist), and as a full grown adult
whether they are at rest, on the water or in the air. There are others, but they
are easy to tell apart, like the crane fly, the dragonfly and the damselfly.
Most of you probably familiar with the life of a mayfly, but for those who don’t,
here is a brief overview. I’ll call this Mayflies 101.
The mayfly life cycle is one of incomplete metamorphous - a big word that means
he or she starts their life as an egg and then as a nymph that has several
stages of growth or instars they are called. In other words they get larger and
larger during the one to two years (usually one) that they are nymphs.
When they hatch, they turn into adult flies, which anglers call duns. In short, the
life cycle of a mayfly is an egg, a nymph and a dun. During its entire life, which
is usually a year but can be two years depending on the species, the mayfly is a
fly with wings only for a day or two, sometimes even less.
Caddisflies and Midges undergo complete metamorphoses which means they
insect start as an egg, then become a larva, then a pupa and finally an
Types of Mayfly Nymphs:
There are basically (4) four types of mayfly nymphs. The swimming nymphs that
actually can swim, some like a minnow and others not so good. In the Smokies,
the Baetis species and most other Blue-winged Olives are swimmers. The
Isonychia bicolor, or Slate Winged Drake is a swimmer is a strong swimmer. The
swimmers are available for trout to eat most of the time.
Then there is the burrowing nymph that lives most of its life in burrows in the
bottom of the stream's soft soil or fine gravel. Most of these are the big drakes.
These are only available to trout some of the time, mainly when they come out of
their holes to eat or hatch. There are only a few types of burrowing mayfly nymphs in
The clinger nymphs can attach themselves to a rock and live most of their lives
under rocks in fast water. They are only available to trout at certain times -such
as just before the hatch. There are a lot of clingers in Yellowstone waters.
For the most part, the crawler nymphs are moderate water nymphs but their habitat can
vary quite a bit. PMDs and Green Drakes are examples of crawler nymphs. They are
available to trout much of the time. There is a moderate amount of crawler nymphs in
A swimmer mayfly nymph looks and behaves as much like a clinger nymph as a
deer looks like an antelope. A crawler nymph looks and behaves as much like a
burrower nymph as a moose looks like a buffalo.
You need to know which type of nymph you are imitating. Otherwise, to be
frank, when you are fishing a nymph imitation, you simply do not know what you
are doing - much less what it is you are imitating.
The Mayfly Hatch:
Near the end of the year or second and even third year in a very few cases, the
mayfly nymphs hatch. In other words, they turn into a fly. They do this by:
1. Swimming to the surface and shedding their nymphal shucks.
2. Crawling to the bank or up rocks or plants to emerge.
3. In some cases, emerging on the bottom and swimming to the surface as a fly.
You need to know which way this activity occurs, when it occurs and
where it occurs for all the mayfly species you may encounter.
Most of them swim or float to the surface (aided by gas bubbles) and hatch into
a fly. During this time they can easily be eaten by trout. This is when we fish an
emerger pattern or a fly that represents the nymph changing into a fly with wings.
If it crawls out of the water to emerge, we don’t need to imitate the dun.
The dun will never touch the water. Slate Drakes do this.
When the mayflies hatch they fly off to the trees or bushes for a short time. They
stay there for a few hours but up to two or three days depending on the species
and the weather conditions. During this time, almost all, duns change into what
we call a spinner. They actually shed their thin shucks, their tails get longer,
and their wings get clearer. In layman terms, they become sexually mature.
After they become a spinner, the males will usually congregate out over the
water. They typically dance up and down, supposedly to attract the females, who
join them shortly afterwards. Then they mate and the males drop dead - similarly
to the way a lot of us older men will probably die.
In most cases, or with most species, the females fly back to the trees, their eggs
develop or ripen, if I get by with calling it such. After a few minutes or hours,
again depending on the species and weather, they fly back out over the water
and deposit their eggs.
1. Some drop them from the air
2. Some dip to the water and drop them
3. Some dive to the bottom and paste them to rocks and plants.
You need to know which way or you simply do not know what your doing when
you imitate the egg laying process. After depositing their eggs, the females die
and fall to the water or if they dive to deposit their eggs, they rise to the surface
and float off.
If they drop their eggs from the air you do not need to imitate the female
spinners at all as an egg layer. You may imitate them dead in what we call a
spent position with the wings flat but not dipping to the water or diving under the
If the mayfly dives to deposit her eggs, you need to be fishing a wet fly to
imitate that activity.
This is a brief overview of the stoneflies. Like the mayflies, stoneflies undergo
incomplete metamorphoses. Again, this simply means they start life as an
egg, change to a nymph and finally an adult. You will see shorty that
caddisflies and midges have another stage of life - the pupa.
Most of the stonefly nymphs are clingers but there are others called sprawlers.
Like the clinger mayfly nymphs they spend most of their life down between and
underneath rocks. For the most part, they are not available for trout to eat until
they move to the banks or crawl upon rocks to hatch.
All of the stoneflies that are important to anglers crawl out of the water to hatch.
They do this on the bottom of the stream. During this time they are subject to
being eaten by trout. This is when the nymph imitation is most effective.
When the nymphs crawl on the bank or upon a rock, they emerge into adults.
The adults quickly fly off into the bushes and other stream side vegetation.
The stoneflies mate and do not return to the water until they deposit their eggs
or otherwise accidentally get into the water. Some of the stoneflies drop their
eggs from the air but most of them actually dip to the water to deposit their eggs.
This is when we imitate the female adults.
Caddisfleis undergo complete metamorphoses. This simply means the caddisfly
starts its life as an egg; then changes to a larva; changes to a pupa; and
finally changes to an adult. Caddisflies and midges have one more stage of life
to imitate than the mayflies and stoneflies.
The caddisfly larva comes in two basic forms - cased and uncased. To get a little
more technical, they come in five basic varieties - the free-living caddises, net
spinners, saddle case makers, purse case makers and tube case makers. The
larvae, uncased or the cased variety, out of their cases look like worms. They
are segmented and have six legs and of course, a head.
When the larvae mature they enter the pupal stage of life for a relatively short
time. The cased variety seal themselves inside their cases. The free-living
variety build retreats and stay there until the metamorphosis is complete. You
may be more familiar with a butterfly that lives in a cocoon in its pupa stage of
life. When the pupae come out of their retreats, they are called pharate adults.
They are fully formed but they are still in a skin with their wings compressed.
This is when most of the species are most subject to being eaten by trout. When
we imitate the pupa, we are imitating the pharate adult.
Most of them emerge on the surface of the water but other species may rise to
the surface and run across the water to the banks. Still others climb out onto
rocks or the bank and hatch into adults.
The adult caddisflies mate in the bushes or on the banks or rocks. The females
return to the water and lay their eggs in different ways. Some deposit their eggs
on the surface. Some skitter across the water, knocking them off. Some crawl or
dive to the bottom and deposit their eggs. Most caddisflies die away from the
water but others die during the egg-laying process. You should know the egg-
laying habits of each caddisfly genus, otherwise, you really do not know what
you are doing when you imitate them.
Midges are another important aquatic insect that anglers need to be familiar
with. It is a mistake to think that midges are not an important food item for trout in
the waters of Yellowstone.
Midge larvae look like tiny grub like worms. There are two types, the ones that
burrow in soft bottoms and the free swimmers that hide under rocks, sticks and
other debris. Yellowstone has both types.
When the midge larvae change go into the pupae stage of life, they are most
subject to being eaten by trout. Most of these pupae emerge in the surface film.
Often, the pupae have a difficult time breaking through the surface skim and
changing into an adult.
The midge pupae look quite similar to the larvae except they have a wing pad
area that is thicker than the body of the larvae. The midge pupa is the most
important stage of life to imitate with a fly.
The adult midge looks similar to a mosquito. They can be important to anglers
during the time they are mating and depositing their eggs. They are imitated with
tiny dry flies.
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Copyright 2008 James Marsh