I was on the river the other day and I wasn't seeing many hatches coming off that morning. I felt kinda perplexed since the trout were turning quickly and I could see them in the clear water grabbing something. I assumed it was midges although I hadn't seen any in the air yet. I caught a fish on a small emerger and that's when I saw what they were keying in on. A small winter stone fly was on the side of my hand. I then realized what the trout were hitting. I knew that by default I had a good fly on. I did change my caddis to a darker body. I spent the rest of the day landing several nice fish. If you see these little guys crawling around its a safe bet that the trout are eating them. They are not very big usually around a size 16 through 20 but in the dead of winter they are a very viable food source for trout. Since they crawl out on rocks or vegetation, there aren't too many emerger patterns. However, I would suggest a black or red copper john as a dropper which will imitate the nymph. You can also tie a elk hair caddis in a black body with a light brown or white wing in size 16 or 18.