Giant Black Stonefly:
The Pteronarcys species, very large stoneflies, are sometimes called the
“Giants". They are clinger nymphs that live for three years. They prefer
moderate to fast currents. The “Giant" stoneflies emerge at dust and continue
well into the evening. The wings of the dorsata, the most common species, are a
dark brown and the body is usually a brown color with yellow tints sometimes.
These huge stoneflies average a hook size 6.
The nymph of the “Giant Stonefly” is by far the most important stage of life. You
will rarely see these mayflies depositing their eggs because they usually do so
during the night. Imitating the egg-laying event is usually only effective if you
fish after dark. This is not very feasible on a fast moving mountain freestone
The nymphs are predators and actively crawl over the bottom in search of prey
that is usually smaller aquatic insects. They can get washed into the current and
drift along the bottom but I would guess that would be a rare occasion. They
are most active at night but imitations can be effective fished late and early in
the day as well as during heavy cloud cover. They are most effective if they are
fished during or just prior to the hatch.
It is not very difficult to tell a Giant Stonefly nymph from a Golden Stonefly
nymph. The nymphs of the Giant Stoneflies have branched gills present on the
thorax and the underside of the first 2 or 3 abdominal segments. The branched
gills are only present on the sides of the thorax and never on the abdominal
segments of a Golden Stonefly.
Copyright 2013 James Marsh
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