This is a much overlooked fly for the simple reason that folks don't know what it is or how to imtitate it. Black fly larva is very prevalant in many streams throughout the world. They are tan in color and have a very noticeable black head along with a black or brown rib. This is a great option in many midge situatations. They range in size from 18-24. Can also be larger or smaller. I've often found that the fish aren't that picky when it comes to the size of this often overlooked fly but sometimes they can be. The smallest I personally have gone is a 22 but most often fish 18 and 20's. Never discount midge or black fly larva paterns in any situation. A good throat sample will show you what the fish are on. Please sample fish 12" or larger. Midge hatches can be difficult. Many times you will never know if fish are feeding. Especially with zero surface activity. This is a great place to start.