Caddisfly Genus Mystacides (Black Dancer)

I've been extremely frustrated several times by trout feeding on Black Dancers, especially on the Brule in Wisconsin. The flies gather in little swarms beneath overhanging alders along the bank, usually within a foot or two of the surface, and "dance" around. A trout or two, usually small, will appear below them and rise steadily.

This is one of the most reliable insect activities on that river in the summer. It's quite unlike any other hatch, since it never affects most of the stream. Instead, there are just little pockets of activity here and there along the bank. It would be interesting to see if some of the trout are Mystacides "specialists" who are conditioned to cruise the banks looking for this food source.

At any rate, I've never had much luck catching these trout. I've tried most often on the Brule but I've run across similar situations on Finger Lakes and Catskill rivers in New York, too. Has anyone cracked the code?