When Gramp tied those thin-bodied ephemerella, as he called them, on size-eighteen hooks, their pale green bodies and diaphanous gray wings reminded us of tiny, unmoored sailboats, and when the duns themselves were adrift upon the surface of the pool, we watched as an entire armada of delicate, translucent ships spun and took flight. . . . I couldn't fish right away. I never can when the duns first come up. I have to watch them, suddenly upon the...