It certainly is open to ANYONE. Needn't participate every single week either.
Just need to know there will be enough interest.
Whoever has the turn names the next fly, so it could be almost anything!!!!!!!
Personally, I'm only into trout flies, so, as an example, I wouldn't participate if a warm water fly were chosen. So, just participate when and if you want. However, gotta have a bunch of people in the mix for it to be of much value IMHO.
Byron