'Boat bug' definitions:

Definition of 'boat bug'

noun

Carnivorous aquatic bug having paddle-like hind legs [syn: water boatman, boat bug]

From: GCIDE

Boat bug \Boat" bug`\ (Zool.) 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. [1913 Webster]

From: GCIDE

backswimmer \back"swim`mer\ n. any of numerous predaceous aquatic insects of the family Notonectidae (such as Notonecta undulata) that swim on their backs and may inflict painful bites; -- also called boat bug. --[RHUD] [WordNet 1.5 +PJC]