Just checked out the link & read it. I've always found there to be a small but noticeable diff between the two- just like one of the replies in that link, the March Brown seems to average a #10 and be a little darker than the Gray Fox, which seems to normally be a # 12 or so. I'm a little fuzzy on the chronological order, but I wanna say the March Brown seems to hatch first, and then you see the Gray Fox. Seeing as they are genetically the same, I wonder if the difference is simply due to slightly different hatching times? I know other bugs are "multi-brooded", the same bug hatching at different times of the year, and they sometimes are smaller and different colored during later dates. Look at the Isonychia- the first heavy batch in June is usually a #10, sometimes even a #8. As you get toward late Summer, it's more like a #10-12, and then sometimes even a #14 and more olive in color as you get into October. What do you guys think?