Tiny Baetis mayflies are perhaps the most commonly encountered and imitated by anglers on all American trout streams due to their great abundance, widespread distribution, and trout-friendly emergence habits.
A work trip took me to eastern Washington this fall, and I took some time to drive far out into the desert and explore a thin blue line on the map, where groundwater flowed through a channel I thought might be trouty. In one spot I wanted to try, the channel was dry, but I hunted around and found water. After a long hike over ground that looked like it should be crawling with rattlesnakes (although I fortunately didn't see any), I stepped in and started looking for trout. There were some.
Fishing mid-afternoon on a sunny day, I was pleasantly surprised to find the first fishable October Caddis (Dicosmoecus) hatch I've encountered. There weren't thick clouds of bugs, just a noticeable number of adults flitting around, enough to make trout that seemed generally lethargic rocket to the surface for anything resembling a decent imitation. One long run lined with bank-side alders, a conspicuous feature on this grassy-banked stream, held an exceptional number of caddisflies perching in the leaves, enough that at least a few would fly away when I shook the trunk of any tree. There were trout below these trees in slow, shallow water that would not ordinarily have held them. It was interesting to to see such a convincing example of trout moving between different habitats to pursue a particular food source.