Some 20 years ago on a Wyoming lake I learned a valuable lesson …. always carry some monster midges in size 12 and 14 because sooner or later you're going to need them. On the day I learned this lesson I was only moderately successful by trimming down a size 12 Adams. Hundreds of fish were rising all over the lake and the swallows were in a feeding frenzy. I ended up catching a few of the less selective/smaller fish!
Last week on the Red Feather Lakes I ran into a monster midge hatch. For about a hour the fish were on these bugs. Every cast produced a strike from a 14 to 18-inch trout.
The point is that you may not need them often, but when you do nothing else will work quite as well.
From the photo you can see that I tie mine with CDC, peacock herl, and grizzly hackle. The body is super fine black dubbing with a white thread or silver wire rib.