In the chapter "Gangsters" of Sag Harbor, Benji Cooper goes out one evening to fight with his friends using BB guns. Benji lies down in an empty lot to ambush people, sees a firefly, digresses about fireflies, and then recalls us from this digression with the impact of a BB pellet at the space between his tear duct and brow.
Benji's explanation of fireflies highlights the fact that people only notice them when they light up. The rest of the time, when they are dark, people don't notice them. In the minds of people, the fireflies may as well not exist when they are not flashing. The people choose to characterize them only by the times when they are flashing; this is why they are called fireflies and not flies-that-sometimes-light-up-but-are-usually-dark. The important thing to realize is that most of the fireflies life is unnoticed.
For Benji during the summer, his parents only see a small slice of his life, since they spend most of the time working. The BB game itself is notably part of his life which he really does not want his parents to know about--this will become a great worry after the BB pellet gets stuck behind his eye.
We've seen many coming-of-age individuals whose parents don't really understand them this semester, and all of these might be represented by fireflies. However, Benji seems to have an especially difficult relationship with his parents, both because of his father's abusiveness and because of his parents' work habits.
