I was in Idaho last week. It's a pretty great state, and if you don't believe me, ask my buddy Zack, who grew up there.
I fished in several rivers: the South Fork of the Snake River, the Big Lost River and the Big Wood River. I caught fish in each but the latter was the most productive for me. I found that the fish there were agreeable to terrestrial offerings; notably, hoppers and small, cinnamon ants.
I had exactly two small, cinnamon ants in my fly boxes. A size 12 Power Ant caught me numerous fish until I lost it on an unexpectedly large specimen in a small backwater flow. I rummaged through my boxes until I found the only other suitable version, which apparently already had some encounters.
The fly fell apart over the course of the next dozen fish until it no longer floated and hardly looked like an ant. I tried a black ant, roughly the same size and failed to raise another fish.
I drove down to the famed Silver Creek, drank a beer while I walked its banks. I didn't make a single cast. Then I hit the road west, for home.