Notonecta undulata

from WordNet (r) 3.0 (2006)

Notonecta undulata
    n 1: predaceous aquatic insect that swims on its back and may
         inflict painful bites [syn: {backswimmer}, {Notonecta
         undulata}]

from The Collaborative International Dictionary of English v.0.48

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]