In late spring and early summer black flies emerge from rivers and make life miserable for man, beasts and birds. Females suck out our blood and leave painful welts.
Here in the Wisconsin area, I've seen them invade the nests of eagles, whooping cranes and peregrine falcons. To avoid the flies, nest babies sometimes jump out like the poor souls in the World Trade Center.
Here's an additional video of peregrine falcons taking down pelicans: The Peregrine Falcon "a Living Missile."