I bet the mayfly was a Hexagenia and they were referring to those blanket Hex hatches they have up at and near the Great Lakes. These hatches are so thick they sometimes shut down highways when motorist start running over the 1000s of hexs on the highway and making the roads to slick to drive on. Lefty said he tried to fish some of these hatches for smallmouth a few times but ended up hunkering down in the boat, covering his mouth and ears and hoping he could see to drive the boat back to the docks.
All a walleye would have to do is swim thru all the nymphs and open his mouth! One pass..full for the night.
For walleye I like Char, Wine, and purple bunnie flies with a dumbell eyes. For sandies I like white, yellow, and olive marabou microjigs.