Today I learned that when the lawn has not been mowed for two months, in the growing season, that when it's finally mowed, the air becomes filled with dust, dirt, and small bits of lawn debris swirling about. But then you realize NO! Those are huge swarms of gnats, a snowstorm of gnats. And they are there for the rest of the day.
So what I learned is, if you're inviting people over for the afternoon, do NOT mow the lawn in the morning! (And in the evening, pray for bats!)