Midges, baseball fans recall, are the gnat-like insects that rose from Lake Erie last October and descended upon Chamberlain in the bottom of the eighth inning of a playoff game against the Cleveland Indians, distracting him into throwing two wild pitches. Cleveland scored the tying run without a hit. The Yankees eventually lost the game and eventually the series.During mating season, the air at Lake Myvatn can also be thick with male midges, each hovering, waiting for a female to join him. “It’s a like a fog, a brown dense fog that just rises around the lake,” said Anthony R. Ives, a professor of zoology at the University of Wisconsin.Yet at the same time in other years, hardly a midge was to be seen at the lake. This boom-and-bust cycle — the density of midges can rise or fall by a factor of a million within a few years — drew the interest of ecologists like Dr. Ives.