A. It sounds very much like the trout were feeding on a small, cased caddisfly larva of the genus Helicopsyche. It constructs its case from sand grains or rock fragments and builds it in a coiled spiral that resembles a snail shell. In fact, it was mistaken for a snail for sometime until someone looked at it closely and discovered that it was a caddisfly, not a mollusk. Helicopsyche is the only genus of the family Helicopsychidae that occurs in North America. Trout readily feed on these and other cased caddisfly larvae.

To be doubly sure, I contacted two colleagues at Virginia Tech to verify that this organism is present in VA streams; one verified that it occurs throughout western VA so is probably also in the northern part of the state. The second said that he has also found trout gorged on true snails, but from your description it doesn't sound like they are molluscs.