They’re so tiny I can’t picture their wings, or their feet, or their mouths. Nor can I understand their neurotic need to nibble my jaw and the oily crease behind my ear. They're only black dots. Yet ask the miners and loggers and tree planters about blackflies in late spring. You will see their eyes shrink and their tough beards tremble.

The living crumbs appear so suddenly that no one can prepare. By the time they arrive, I’ve just about met everyone in the camp. My legs and lungs feel strong as I plunge my fingers in soil, hop over tree trunks and wipe myself with sphagnum moss. The blackfly, however, feels the same way. It follows the claw of its appetite.

I first met swarms of them in Hearst, Ontario, where the black dots clustered into clouds and blotted out the sky. I threw my ...