Notes on Caddisflies (Trichoptera)
"Most caddisfly larvae live in cases they build out of sand, rock, twigs, leaf pieces, and any other kind of underwater debris. Some even generate their own cases out of silk. There is tremendous variation in case style and also in the way the larvae manage their cases: whether they replace it as they grow or renovate their old one, and whether they carry it around or fix it to an object. Trout love to eat these larvae, case and all.
Other common caddis larvae build nets instead of cases. These are not residences but hunting traps, like tiny spider webs, designed to capture plankton and smaller aquatic insects the larvae eat. One larva may build more than one net and roam freely around the rocks and logs tending to each and ingesting the catch. The net-spinning families, in order of abundance, are Hydropsychidae, Philopotamidae, and Arctopsychidae.
In many species, the pupae become very active just before emergence and drift along the bottom of the river, sometimes for hours. The "deep sparkle pupa" patterns introduced by Gary LaFontaine in Caddisflies are the most popular of many imitations inspired by this behavior. It is a deep nymph fisherman's dream. Sometimes they drift similarly just below the surface for a long time before trying to break through.
Pupae of different species use three different methods to emerge:
Most species rise to the surface and struggle through. They usually take flight quickly once they're out of the water, but slow species first struggle and drift long distances half-submerged as they wriggle free from their pupal shucks.
-The pupae of some species crawl out of the water on rocks, sticks, and such, so that the adults emerge high and dry.
-Some pupae rise to the surface and swim quickly across it to shore where they crawl out to emerge.
-Most caddis pupae are good swimmers, and they use their legs as paddles rather than wiggling their bodies to move.
After emerging, caddisfly adults live for a long time compared to mayflies, in part because they are able to drink to avoid dehydration (mayfly adults cannot eat or drink). This flight period lasts anywhere from a few days to a few months, depending on the species, so mating adults may be seen on or over the water long after emergence is complete."
-Troutnut
http://www.troutnut.com/hatch/12/Insect-Trichoptera-Caddisflies
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