Our insect this time is one of the common freshwater crustaceans.
There are over 1,100 known species in just North America! They
live in all kinds of freshwater places, usually for our purposes though,
in tailwaters and spring creeks.
These crustaceans are very important food sources for fish. The two
larger forms are the Aquatic Sowbugs Ispoda and
the Scuds Amphipoda. Since both are about the
same size, 5 to 20 mm, we are lumping the two together here.
The Asellus shown left is the most important of the sowbugs, with about 100
species. They live in a variety of shallow freshwater environments,
among rocks and decaying leaves. The common name for sowbugs,
(and sometimes the scuds too) is cress bug since they are found in
spring creeks and other clean, clear water which grows watercress.
The fly which imitates the sowbug in slow-flowing water with
considerable plant growth is the American Sowbug.
There are several important species of scuds. The group totals about
90 in North America. Most are found in the same places as the sowbug,
with one important exception. The family Haustoriidea has only one
species in North America, and it is important because it is found in
an entirely different environment! The Pontoporeia hoyi
lives on the bottom and open waters of deep, cold lakes.
The most important specie to fly fishers is the Gammarus.
This one also lives primarily in shallow waters of all kinds.
They have a strange habit, as they swim they move to the side, and
are called 'side swimmers.' These are not shrimp, although in Canada,
scuds, sowbugs and shrimp are all called freshwater shrimp. Colors are
varied, from grays, browns and cream to the most common olive and greens.
Scuds are interesting in the fact when they are disturbed or under attack,
they roll up, like an armadillo. That may be why the so-called scud hook
was invented. In reality, the scud when swimming, swims straightened out.
The body at rest or swimming is not curved.
Tie your imitations on a stright-shank hook.
There are many specific fly patterns for nymph fishing based on scuds.
These include the Yellow Freshwater Scud which imitates the
Gammarus minus, Olive Freshwater Scud Gammarus
fascaitus, Tan Freshwater Scud Crangonyx gracilus
, and Tiny Olive Scud Hyalella azteca. Others
include Werner's Shrimp, Otter Shrimp, Nyerges Nymph, Henry's Lake
Nymph, Big Horn Shrimp, Yellowstone Scud, Fred Arbona's Scud, and
the Troth Scud.
Scuds do not hatch. They don't crawl out of the water like the large
stoneflies and become wonderful winged creatures. The adult forms
shown here are all there is.
Your best bet to catch fish on scuds in lakes is to get your fly down
to near the bottom. A weighted fly is the answer in deeper water.
Retrieve very slowly. Folks have called scud fishing
the most boring of all, since the retrieve should be about as slow as you
can stand it. In water deeper than five feet, a sinking line is recommended.
For spring creeks and tailwaters, a floating line with a strike indicator is the
way to go. Use a normal nymphing technique, but with again a very slow
retrieve. Your fly needs to be on the bottom of the stream bed.
For more on scuds and the flies, read
Tailwater and Spring Creek Favorites,
Al's C-B Scud, and Sowbug.
Credits: Information and drawings from Aquatic Entomology by W. Patrick
McCafferty, published by Jones and Bartlett.