.......................  ....................  ...Fly Fishing Yellowstone National Park
4/29/12

New KISS Bug Series - Part 5
Bugs 101

Stoneflies 101:
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 change into an adult. You
will see shorty that caddisflies and midges have another stage of life - the pupa. They undergo complete
metamorphoses.

Stonefly Nymphs:
Most of the stonefly nymphs are clingers but there are others called sprawlers. Those that are sprawlers
are not of interest to trout anglers. Like the clinger mayfly nymphs, they spend most of their life down
between and underneath rocks and cobble on the bottom of the streams of Yellowstone National Park. For
the most part, they are not available for trout to eat until they move to the banks or are in the process of
crawling upon rocks or bank to hatch. At that time, they are very exposed to the trout.

All of the stoneflies that are important to anglers crawl out of the water to hatch. They do this by crawling
across the bottom of the stream, not drifting mid-stream  During this time, meaning the time it takes them to
cross from their normal fast water habitat to a rock or boulder that protrudes out of the water, or to the
nearest bank, they are very subject to being eaten by trout. This is when the nymph imitation is most
effective.

Stonefly Adults:
When the nymphs crawl out of the water on the bank or upon a rock, they emerge into adults. Trout would
have to jump out of the water to eat them on the rocks or the bank to eat a stonefly at this stage of life. In
other words, there's not any need for an emerger fly pattern for a stonefly. 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 are
ready to deposit their eggs. It is possible, especially during high wind conditions, for them to get into the
water accidentally.

The egg laying event is the thing that creates the dry fly action for the angler. 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 adult females with a dry fly.

Copyright 2012 James Marsh
Little Yellow Stonefly
usually called a
Yellow Sally are
plentiful in the
streams of
Yellowstone
National Park.