I'd rate them: a swarm of muffleheads, biting black flies, mayflies. Mayflys don't bite they just make a mess. My experience is they don't bother you much on the water and if they do you can get away from the hatch. Their hulls are ugly and they probably mess up the fishing but I think they are mainly an onshore problem. My question is how is the hatch in Huron. I'm planning to come up Monday and I'm trying to figure out if I need to bring the cover for my boat. Any update from someone onsite would be appreciated.