12/10/09

Basics of Fly Fishing: Trout Food Series - Answers to the Top
Questions on Caddisfly Larvae
Now remember, after the introduction in lesson #1, our Trout Food Series started
with the top ten things trout eat (Lesson #2). It proceeded though the top 10 trout
foods in the Smokies (lesson #4) and the top tips on the stages of an insect's life
(Lesson 5). If you do not remember the these lessons, you should go back and
review them. So far, the only insect we have covered in general, meaning
non-specific species, is the mayfly. This lesson #12 starts the general series on
caddisflies.

1. How does the caddisfly differ from the mayfly?
The mayfly has only two stages of life that trout eat - the larva stage (nymph) and
the adult (dun). The dun becomes sexually mature and changes to a spinner but
that isn't a stage of life. The caddisfly has three stages of life and trout eat some
caddisflies in all three of these stages - the larva, pupa and adult stages.

2. What is a free-living caddisfly larva?
Some species of caddisflies do not have cases. The ones that don't are called free-
living caddisflies. Often these are called worms. The Green Rock Worm is the name
of a fly that imitates a free living caddisfly of one particular group of caddisflies.
These larvae crawl around on the bottom in search for food. They hide down
between and under rocks on the bottom of the stream but they are for the most
part, always exposed to the trout.

3. What is a net-spinning caddisfly lara?
A net spinning caddisfly larva is one that lives in a shelter that partially covers the
larva but goes outside of its shelter to eat. These shelters are little canopy like
structures with one end of them open. Net spinners also build tiny nets that catch
their food. These larva suspend themselves on a silk line attached to their shelters
so that they can eat the food caught in their nets and then repel themselves back to
their shelters. They are similar to the free-living caddisflies but they have these
shelters to live in and the nets to capture their food. Trout can eat them easily when
they are outside of their shelters.

4. What is a cased caddisfly larva?
A cased caddisfly larva lives in a case it builds from different materials in the stream
it lives in. Some are made of tiny sticks of wood and others are made of sand,
gravel and other hard materials. Different species of caddisflies build different kinds
and shapes of cases. In fact, it is usually fairly easy to identify the cased caddis
species from their cases. These cases have one end open so that the larva can
stick their head and front legs out and crawl around.

5. How long do caddisfly live?
Except for a few species, caddisflies have a one-year life cycle. The big difference
in them and mayflies in this respect is the caddisflies tend to live much longer out of
the water than mayflies do. Whereas many species of mayflies only live as an adult
fly for a day, most caddisflies live from a few to several days.

5. Are caddisflies eaten by trout in their lava stage?
It depends on the species of caddisflies. Some of the larger case builders are not
eaten, or at least not frequently eaten, but most of the cased caddisflies are. Lava
and cases are found in the stomach of trout. The free-living caddisflies are
commonly eaten by trout. The net-spinners are also commonly eaten by trout. In
fact, trout probably eat several times as many caddisfly larvae and they do the
pupae and adults combined. That's mostly because caddisflies spend over 90% of
their lifetime as larvae.

6. What are the most plentiful types of caddisflies?
By far the most plentiful types of caddisfly larvae are the net spinners. They
probably represent as much as 60% of the caddisfly population in trout streams.
That's an average. The Smokies do not have that high of a percentage of the net
spinners. Streams of the Smokies probably have far more cased caddisflies than
the net spinners. They also have a fairly good population of free-living caddisflies.
The net spinners must have water with a high content of algae and that doesn't
exist in most of the streams in the Smokies. Abrams Creek is the only big exception
to that. It has algae and plenty of net-spinning caddisflies..


Copyright 2009 James Marsh