boat fly

from The Collaborative International Dictionary of English v.0.48
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]
    

[email protected]