The famous nocturnal Hex hatch of the Midwest (and a few other lucky locations) stirs to the surface mythically large brown trout that only touch streamers for the rest of the year.
These interesting insects are not mentioned in trout fishing literature, but they turn up once in a while in my Eastern samples and I understand they are also common in the Midwest.
Larva & pupa biology
The larvae very much resemble pennies from one side. Their whole bodies are an excellent suction cups, their legs are strong for clinging to rocks, and they are somewhat translucent and extremely well-camouflaged. The result is an extremely well-adapted fast-water insect which probably rarely if ever ends up in the drift for the trout.