Harold F. Blaisdell, The Art of Fishing With worms and Other Live Bait, New York, Knopf, 1977, p. 81-82.

I have already indicated that the larvae of the caddis fly are another very deadly trout bait. Fortunately, they can be gathered far more easily, to say nothing of much less painfully, tha, can hornet grubs ! By some mysterious means they encase themselves in woody material from which only their heads ans short legs protrude. They anchor themselves to sunken rocks and logs, always in plain view and but thinly disguised by the sticklike appearance which results in the name «  stick caddis ». They can be picked up by the dozens in most trout streams of the Northeast.

To the best of my observation, stick caddis do not constitute a major item of trout diet, probably for two raisons. First, the larvae usually cling to objects in the shallows and backwaters which trout seldom invade. Second, it seems likely that the trout take a dim view of the woody casing. Examination of stomach contents reveals that trout occasionally gulp them, case and all, but it is very rare to catch a trout whose stomach is jammed with them, as would certainly by the case if trout fed on them eagerly.