The Collaborative International Dictionary
boat fly
Boat bug \Boat" bug`\ (Zo["o]l.) An aquatic hemipterous insect of the genus Notonecta; -- so called from swimming on its back, which gives it the appearance of a little boat. Called also boat fly, boat insect, boatman, and water boatman.
Usage examples of "boat fly".
Although Aunt Zelda had seen the boat fly once before, when the dragon had done battle with DomDaniel's ship, the Vengeance, she had only caught glimpses in flashes of lightning.