water-bug
Wa"ter bug`. (Zoöl.) (a) The Croton bug. (b) Any one of numerous species of large, rapacious, aquatic, hemipterous insects belonging to Belostoma, Benacus, Zaitha, and other genera of the family Belostomatidæ. 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.