I believe the size is related to sex, the bigger fly being female, at least that's the way it usually is. The paler ones are the females.
In the eastern part of the state, we don't get the early hexes, our hatch in August and Sept.
These are the days to go see the Pirates play and see everyone in the stands freaking out about the hexes. Showed a few people in my office the hex and the first thing out of several peoples mouth was... "are those stingers?" Funny what we take for granted as basic knowledge others are just clueless about.
Funny thing is I've never fished the hexes here. It's all LARGE warm water rivers around me and just haven't prioritized fishing the hatch.
I've seen them more and more over the last couple of years. I figured the larger was female but holy hell was she big. Dwarfed any other females on my car hood last night. Solid 2 5/8" body length. And I didn't even get stung. LMAO