I can't remember many summers, if any, that we had significant fireflies into mid-August.  Extensive Google research corroborates my memory and indicates that fireflies typically emerge as adults until about mid-July, and live for two weeks to breed.  While exact timing will vary, the story is that after August these guys should be on their way out. Well it's basically mid-September and they are all over the f'n place.  They are on the lawns in Piscataway, there's a billion of them in the g