I remember stopping by the Snake river right by Yosemite once on a whirlwind dash through the park. There was an RV parked in the pulloff, with some nice chairs set out. We said "huh, wonder why they aren't out in those chairs enjoying the scenery?" We got out of our car, and literal clouds of mosquitoes descended. It was like something from a sci-fi movie, except you don't lose blood in the audience. We got back in the car very quickly. "Oh, so THAT'S why they aren't out in the chairs, enjoying the scenery. They are in their RV getting IV plasma."