280 days of Urbpandemonium #140
I first noticed these very small (less than a mm long) flies when I was at work softball games. It turns out that sitting in a grassy field in summer is surefire way to encounter them. You increase your chances if you bring a dog with you, as the flies are drawn toward the mouth, ears, eyes, and anus of your companion. These are Chloropidae*, variously called frit flies, grass flies, or tellingly, eye gnats. Their larvae feed in the stems of grasses, while the adults seem to slake their thirst on sweat, tears, and other vertebrate bodily fluids. Some species, I am alarmed to report, are known to be vectors of conjunctivitis.
* "green eyed family"