The Collaborative International Dictionary
boat bug
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]
Wiktionary
boat bug
n. An aquatic hemipterous insect of the genus (taxlink Notonecta genus noshow=1); the water boatman.
WordNet
boat bug
n. carnivorous aquatic bug having paddle-like hind legs [syn: water boatman]