Hatches Made Easy:

Giant Stoneflies (Pteronarcys species) - Nymph and Adults


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 2. The streams of the Smoky
Mountain National Park have a huge population of these stoneflies.
The nymph of the “Giant Stonefly” is by far the most important stage of
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 stream. In addition to that, it is not legal to fish beyond 30
minutes after official sunset in the park.
That simply means imitating the
adult is not a viable option.
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 occassion. 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.
Matching the size, shape and color of the stonefly nymph is the important thing.  
Our hatch chart shows these insects hatch from the last week of April until
through the first week of June.
These are the species of Giant Stoneflies listed for the Smoky Mountains
National Park:

Pteronarcys dorsata  
Pteronarcys proteus  
Pteronarcys scotti  

About the only clue you will have that the Giant Stoneflies are hatching is finding
a shuck or empty skin of the nymph left to dry when one of the large stoneflies
changed from a nymph to an adult or fully grown fly. When you start seeing
shucks on the rocks and banks of the stream you can be assured the Giants
have started to hatch. Unless you search the high limbs of trees or search the
sky early in the mornings or near dark, it is rare you will spot an adult.

Coming Up Next:
Giant Stoneflies.- Nymph Presentation & Fly Pattern Colors

Copyright 2008 James Marsh
Giant Stonefly Nymph
Giant Stonefly Shuck