Any one of numerous species of large, rapacious, aquatic,
   hemipterous insects belonging to Belostoma, Benacus, Zaitha, and other
   genera of the family Belostomatidae. Their hind legs are long and
   fringed, and act like oars. Some of these insects are of great size,
   being among the largest existing Hemiptera. Many of them come out of
   the water and fly about at night.