Scott, I've seen many times when the fish seem so gorged on the hatch dujour that they ignored even naturals floating by. Once, while fishing the upper Teton River just west of Driggs, ID, I experienced a massive caddis emergence. The caddis were so thick that every breath was dangerous. Fish were rising all around so I naturally put on my best imitation of the caddis in the air and on the water. an hour later, not even a look and a refusal. I looked closer and realized there was also a massive PMD spinner fall occurring, although how they could make it to the water in the midst of all those caddis is beyond me. There were both female (olive) PMD spinners in size 16 as well as male (rusty) PMD spinners in size 18 on the water. I found the fish preferred the size 18 rusty spinners - the smallest offering on the water at the time. I had a blast touching at least 3 dozen fish before it became too dark to see. I assume the resident trout were gorged on the caddis pupae, because the only fish I caught were whitefish on the surface! Not one trout in the bunch.

It was a blast, but very confusing at the time.

I have seen the trico spinners fall en masse on the Box Canyon of the Henry's Fork in the early morning hours without a fish rising to pay them any interest. I've also been on Utah's Green River when the cicadas are dropping on the water only to watch a finicky brown come to the surface to a floundering bug and do a complete 360-degree inspection of the natural and then refuse and slowly make its way back down to the depths.

Who knows what goes on in that pea-sized brain, but whatever it is, it keeps us all going back for more.