I think where the entomology part comes into play when knowing when each insect hatches and where... Then again, you can just tell your pal down stream when he asks, "Hey, whatchya usin", I'm using a size 16 BWO. We know that if we're in late May through the end of June, he is most likely using a Cornuta.
Take a look at the Grey Fox and the Summer Sulphur... I use the same patterns for both. They're identicle in every way as far as I can tell, and my eyes are still pretty good. The Grey fox previously 'Fuscom' is now 'Vicarium' because they figured it's the same insect as the March Brown. Have you seen these two insects next to each other? The March Brown is definetely the larger of the two. Hatches II says the opposite and I'm not going to argue with Al, but, I've raised both species in a controlled environment too and from my observations, this is what I've noticed. I'm no entomologist, but it doesn't take an entomologist to tell the two apart either (most of the time). So, why not move Stenonema Ithica into Vicarium too? Anyhow, If you're with your pal and he ask what your using, just tell him the size and common name.