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Trout
Stream Insects
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Here is a
brief description of the four main insects of a Trout's diet.
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Mayfly Nymph
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Mayfly Dun
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| Mayfly-
(Ephemeroptera) Their upright wings are very characteristic
of the mayfly. Most common sizes are ½" - 1½" long. Mayfly
eggs are laid on the surface of the water, usually in riffles (although
they can be found in many stillwaters) in the evening. The eggs
hatch into the nymphal stage where they will live under water for
about one year. At the end of this cycle the nymphs swim to the
surface film and hatch into the dun stage. They will float on top
of the water (dun) drying their wings,
resembling a sailboat. Next they will fly into the trees and mature
into an adult in a day or two. Then the mayfly will mate in midair,
often called spinner, the female will
lay her eggs and then fall into the water with their wings spread,
called spent or dead. |
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Stonefly Nymph
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Stonefly Adult
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| Stonefly-
(Plecoptera) Most have very noticeable antennae, a wing
that covers most of the body, and two short tails. They range from
½" - 1" long, and are clumsy in flight. Nymphs usually
are found in fast moving water. They are easily identified by their
two tails. Nymphs crawl onto rocks or shore to hatch. Once out of
the water they hatch into adults and the female lays her eggs into
the stream. |
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Caddis Larva
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Caddis Adult
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| Caddisfly-
(Trichoptera) Adults have folded wings like a tent, in
flight they are very erratic and resemble a helicopter. Most are
about ¼" long, but of course their wings are much longer than
their bodies. They spend the majority of their lives on the bottom
of a stream or lake. Caddis begin in the larval form, they make
cases out of sand or debris. They can be found clinging to rocks,
logs, or just walking along the bottom. They can become Trout candy
if they become separated from their case, since they cannot swim.
When they are ready to emerge the larvae change into pupae and use
their legs and wings to swim to the surface. They hatch into adults
and swim away. Females drop their eggs on the surface of the water,
they tend to skitter over the surface. |
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| Midge-
(Diptera, member of the Chironomidae family) They resemble
mosquitoes. Midges spend most of their lives in the larval stage
on the bottom. They turn into pupae and float to the surface and
tend to hang in the surface film. Then they hatch into adults and
swim off very quickly. Trout love them because they are loaded with
protein. |
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One final thought in identifying
nymphs. Nymphs that have two tails like the stonefly are crawlers.
They crawl along the streams bottom and tend to cling to rocks.
Three tailed nymphs like the mayfly are swimmers, they tend to swim
and hatch in the water.
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