A Brief Overview
Learning entomology, even
in basic terms, is very important in helping a fly fishermen
become more successful. Knowing what insects are hatching,
what stage the trout are taking, or having a good idea
of what to expect, can be the difference in a frustrating
or successful night on the water. Understanding entomology
will also help to identify rising fish forms (check
out the section on "feeding patterns"), where to look
for fish during certain hatches based on what types
of bugs they are, or knowing what to select from your
box with an understanding of how to drift or present
that particular fly.
The life cycle of a mayfly
A mayfly has four life cycles that should concern fly
fishermen. The nymph, emerger, dun, and spinner. All
of these cycles represent important stages that trout
feed on. The nymph takes up the majority of a trout's
diet. This is when the mayfly is in its beginning stages.
A nymph will molt several times spending its time beneath
rocks and buried in the stream bed growing to size in
preparation to hatch. Trout feed on nymphs when they
begin to move out from under rocks, and drift down river
as time nears for them to hatch. Nymph fishing is usually
best early morning and midday when the nymphs begin
to move and drift downstream. Fishing nymphs that are
the predominant hatch occurring or one that will be
on the water in the near future will increase nymph
An emerger, at times not considered a stage in a mayfly's
life cycle, is when a mayfly begins to either rise to
the surface, crawl onto shore, or shed its skin beneath
the water in preparation to hatch (they hatch several
ways depending upon specific bugs). This is a very important
stage, because the mayfly is very vulnerable. Many mayflies
are eaten when they are an emerger because they are
still subsurface, making this an important stage to
understand. Trout feeding on an emerger can usually
be seen visually as a dry fly feeding fish. Many people
mistake a trout feeding on an emerger as a fish taking
a dun (adult mayfly). This can easily be distinguished
by watching the way the fish is feeding. If the trout
is rising dorsal fin, tail, then kicking down either
creating a bulge or splashy rise it is usually feeding
on an emerger. Large trout feeding on emergers usually
just create a bulge. The key is to see if the fish is
showing its head, and if it is not then it is usually
feeding on an emerger just subsurface.
The dun or adult mayfly is the stage most fly fishermen
dream about. Seeing a hatch of mayflies, or being in
the middle of one is a wonderful experience. These bugs
hatch either under the water and swim to the surface,
hatch on top of the water, or crawl to shore or a nearby
rock to shed its shuck. At this time mayflies can be
seen in the air, riding the water's surface, or fleeing
to a nearby tree to await for its reproductive organs
to develop. When the mayfly is fully developed it will
mate preparing the female for egg laying. Once the mating
process is taken care of the females will fly to the
water and deposit their eggs. Some will fly up and down
off the water depositing eggs or even dive underwater
to lay eggs which settle to the bottom adhering along
the stream bed. These eggs will be the next generation
for the following year (a few mayflies will take longer
or shorter to develop). Fishing mayfly duns is a tremendous
and exciting experience. The last stage of a mayfly
is the spinner. After it has mated and deposited eggs
it become weak, and eventually dies. Most spinners fall
in the evening which in turn represents the term "evening
spinner fall". Some mayflies can be found spent during
the morning hours, Tricos being a good example. Spinners
are an easy meal for trout. They are completely dead
and flat on the water. Trout don't have to expend any
energy to feed on this stage. You will often see trout
gently sipping spinners off the top. Large trout especially
understand what it is to use as little energy as possible
to feed on these easy targets. Spinners should be fished
with the least amount of drag possible (no drag at all
is best). Devoting a fly box to just spinners is not
a bad idea.
Four types of mayflies -Tips on where and
how to fish them
There are four different types of mayflies: clingers,
crawlers, burrowers, and swimmers. Each different type
of mayfly includes a variety of mayflies and hatches.
It is important in understanding the four stages of
mayflies especially on large river systems.
Clingers like fast moving water and that is why they
are built flat and broad to hang onto rocks in fast
currents. So mayflies such as March Browns and Light
Cahills which are clingers can be found in areas of
hard pushing riffles and runs. If you find an area of
river or stream that has an abundance of fast moving
water, this is where you may find your best fishing
with clinging type mayflies. Clingers also tend to jump
out of their shucks faster then some other mayflies.
This makes them a good choice to imitate with a slow
swung wet fly rising steadily to the top. These mayflies
tend to be a little more sporadic of a hatch, yet can
still offer excellent dry fly fishing.
Crawlers are usually found in areas of soft riffles
and runs during their stage as a nymph. These bugs such
as Hendricksons and Sulphurs usually have a hard time
hatching from their shucks. The crawler family represents
the largest family, and offers the best fishing with
dead drifted emergers just in or below the surface film.
The duns of these bugs can hatch in prolific numbers
sometime blanketing the water. They also fish well tied
with trailing shucks.
The burrower family represents some of the larger mayflies
such as Green Drakes, Brown Drakes, and Hexagenia. These
mayflies are found in better numbers in and around silt.
Areas of rivers with a good soft bottom will harbor
these mayflies best. These mayflies need the silt to
burrow and live as a nymph. These hatches attract some
of the most anglers, and are usually very prolific but
short lived. The spinner falls of these mayflies are
very often outstanding fishing. Swimmers such as Isonychias
like a combination of large soft moving pools, riffles,
and runs. These mayflies fish excellent as a fast swung
wet fly or even as a dun in an area of swift moving
water. These bugs can swim very fast so don't be afraid
to swing these wet flies quickly, and use heavy tippets
as strikes can be vigorous. These mayflies can hatch
both in sporadic and heavy numbers.
insects and their importance
Caddis, stoneflies, midges, and terrestrials all play
a big factor along with the mayflies in a trout's diet.
Caddis and stoneflies like mayflies go through an important
life cycle which when understood will help every fly
fishermen become more successful.
The four stages can be found in a caddis that can in
a mayfly. Nymph (often called a pupa for a caddis),
emerger, dun (adult caddis), and spinner (spent caddis).
Caddis pupa are basically the same as a mayfly nymph
and can be fished in the same manner (dead drifted near
the bottom). Caddis emergers can be fished just below
or in the surface film. Caddis emergers can also be
swung, as caddis swim to the surface at a fast pace.
Trout can often be seen exploding with an escaping caddis
emerging from the trout's chase. Caddis duns can also
be fished with a dead drift or skated presentation.
These flies tend to hop on skitter on top of the water.
Larger trout usually don't expend the energy to chase
adult caddis. Spent caddis are very important, as with
mayflies they present an easy meal for trout.
Stoneflies come in a variety of sizes and colors. They
can be anything from a size 2 or 4 up to a size 18.
They are an important bug especially in the nymph stage.
Stonefly nymphs present a good majority of the fish
caught during the trout season. They are often large
easy meals for trout. Stoneflies usually aren't known
for being fished in the emerger stage, because they
crawl out of the water to hatch. They can be fished
in this stage especially at night with a large wet fly.
Fishing these wets behind boulders and in seams where
struggling emerging nymphs fall off of rocks or drift
into awaiting trout can be very rewarding. Adult stoneflies
can also be extraordinary fishing either late evening,
nighttime, or early mornings.
Midges are important especially to smaller streams with
less mayfly activity. They can present some of the best
fishing when other bugs are not around. Fine tippets
and long leaders are usually a must to fish these tiny
Terrestrials are also an important food supply for trout.
On smaller streams summertime terrestrial dry fly fishing
can be great especially under overhanging trees. Ants,
beetles, crickets, and inch worms are some of the important
terrestrials to have in your box. Many times even on
prolific large rivers, terrestrials such as flying ants
can steel the show from the many mayflies covering the
Overall, learning entomology is very important to fly
fishermen of all skill levels. Whatever level you take
learning entomology too, it will help you to become
a more successful and less frustrated angler. Getting
out on the water, turning over a few rocks, and having
a good book on entomology will dramatically increase