Entomology      

Trichoptera
(Caddis Fly)

  Adult Caddis Fly  Life Cycle 

   Caddis - flies (Trichoptera) is the most  important aquatic insects in The known world, and a passionate fly fisher should
    know as much as possible about these  insects. These hairy little insects with  their long antennae and their sort of
     clumsy flight seems to be rather primitive insects, but this is totally wrong. In fact, the Caddis flies
     are among the more developed insects in the group. Holometabolic (insects with a complete metamorphosis) in the
     under group Pterygota. They are among the 'youngest' insects,   'only' about 140 - 180 million years old.
     The figure on the left shows that when the egg hatches, a  Caddis larvae comes out. What this little larvae does after
      hatching depends of what kind of Caddis larvae it is. If it builds  itself a house, or not. Some Caddis larvae build themselves
   houses of materials from their environment to use this as protection, and some of them is spinning silk nets.
 Used both as  protection (mostly camouflage) and as a mean to catch food. Other species are living as free larvae.
The grown insect does remind a bit of a Butterfly, but the wings are covered with hair - not with shells. The colors are mostly
grayish or brownish. The Caddis larvae is an important part of the trout's food. Each of the different kind of house building
Caddis larvae has their own characteristic house type. They can use small sticks, stone, sand, even small snail houses-
Sometimes even with the snails themselves inside. Inside these houses there is always a silk tube spun from the mouth of the
larvae, and the other materials is attached to this inner silk tube.
This type of larvae has a soft, light colored abdomen with three outgrowths on the first segment, used to keep the insect on
place inside its house. Along the body there is gills, sucking up oxygen from the water. The head ant the thorax is covered with
a shell that is darker than the abdomen. Larvae like this is crawling on the bottom with the head and the feet outside the
house. But as soon as a danger is spotted, the whole body is redrawn into the house.
This means a major change. The larvae changes skin, and gets a pupa skin. Inside this new skin another major change is
going on, and the pupae goes through a metamorphosis to the winged insect
Different opinions
The exact way this «hatching» happens is not too well known, and it's a lack of research on this issue. Some experts claim that
the pupa as soon as it has freed itself from the house swims or crawls to the surface to hatch and fly off. Others say that the
pupae's after they leave the houses are swimming around, or even drift long distances with the current before swiftly getting to
the surface. On the surface they can drift for a period of time, depending on the temperatures and weather - before they
suddenly hatch and flies off. Maybe we fly fishers can help out explaining what's really going on...
In this stage the Caddis flies can drink fluid, as a contrast to the May-flies. This
fact makes the Caddis fly able to prolong their lives quite a lot, to 20 days or
more, depending on the weather conditions. During this period of time the
Caddis flies mates several times, since they do not die after mating and the laying
of eggs like the May-flies. The mating mostly goes on over dry land.
When the Caddis flies are laying eggs, this can happen in several ways. The female
can fly out over the water, and dip the abdomen into the water and lay her eggs
this way. She can even swim around in the surface film while doing this. Another
way is placing the eggs in a damp area at the shoreline, from where the larvae
later can crawl by themselves into the water. The most usual way though, is that
the female crawls down into the water, and attach her eggs to the material on
the bottom. If she is not eaten by a hungry trout during this risky business, she
crawls up to the surface, and flies off. Maybe to mate again.
We will find Caddis Imagoes (grown, winged insects) during the whole season in
Most of Europe. From March/April until September/October. Naturally there are most
of them in the spring- and summertime. The temperature is important, and in the
mountain areas the hatching happens later than in the lower parts. In fact, there
is no "springtime" in the high mountains. The snow and ice is laying there - and
suddenly the warmth is coming, and the hatching is extremely heavy.  The
fly fisher that is lucky enough to be on the right spot on any stream or river when
this happens, might remember the experience for a long time.
The Caddis flies are some tough little creatures, and can take quite a lot of
pollution (at least some forms of it). One of the things they handle quite well is
acid rain. In waters with a pH 4 until about pH 9 you can find caddis flies.
Their demand on Oxygen is about the same as normal fishes, and they can
therefore be whipped out if the waters are strangled. They can also take more
contents of other things (Humus as an example) than do the May-Flies. A real danger for all such insects is
extremely big differences in water height. They are, like all other food species for fish, living near the shores.

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