Hatches Made Easy:

Dobsonflies and Fishflies (Corydalidae Family)

6/03/08

The Dobsonfly is probably more familiar to most of you in the larva stage of life
called the Helligramite. I am sure that if you have ever caught any nymphs you
have seen the helligrammite. I am also sure that if you have ever picked one up
you quickly learned one difference in a mayfly or stonefly nymph and the
helligrammite. They can and will bite and pinch.
These flies deposit their eggs on the bottom side of leaves and stems of the
bushes and trees. The eggs hatch into larvae and fall off into the water where
they live until they hatch.
These larvae are predators that eat other insects. The adult Dobsonfly is a very
large fly that looks a lot like a stonefly. They are nocturnal, so it is doubtful you
will see them very often in the daylight hours. The adults only live a few days
during which time they mate and deposit their eggs in the darkness.
I am sure the opportunistic trout would eat one of these flies if it accidentally fell
into the water. I don't think they warrant a dry fly pattern although there are
anglers that would disagree with me. The larvae are readily eaten by trout as
well as smallmouth bass. I mention smallmouth because the dobsonfly tends to
dwell in slightly warmer water or water that is marginal for trout.
The streams of the Great Smoky Mountains National Park have a lot of these
insects. We have found huge quantities of them in water samples taken from the
spring creek portion of Abrams Creek. Most all the small streams at the mid to
lower elevations have fairly large populations of the larvae.
The Dobsonfly can easily be confused with the smaller fishfly. Both are in the
same family. Both have very similar behavior so I don't think it is necessary for
me to discuss them separately.

These are the known species of Dobsonflies and Fishflies in the Great Smoky
Mountains National Park:
Chauliodes pectinicornis   Fishfly
Corydalus cornutus  Dobsonfly; Helgrammite; Grampus Fishflies
Nigronia fasciatus  Fishflies
Nigronia serricornis

Presentation:
The Dobsonfly larvae, or helligrammite, as well as the fishfly larvae are much
worth imitating. The helligrammites can be found in the riffles. The fishflies are
more frequently found in the eddies and backwater or slow water areas of the
streams. Fish the imitation exactly like you would a clinger mayfly nymph
imitation. You need to keep the fly on the bottom by weighting it down. Most of
the time an up or up and across presentation works best. Short line nymphing or
"high stickin" also work with the helligrammite imitation.

Coming Up Next:
Alderflies (Sialidae, Genus: Sialis)                

Copyright 2008 James Marsh