Water bug : The Croton bug.

Water bug : 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.

Example:


Taxonomy
eggs, species, family Belostomatidae, females, order Hemiptera, bugs, Lauck, genus, Belostoma, insects, free encyclopedia, Belostomatinae, Lethocerinae, mate, Heteroptera, monograph, Bulletin, Chicago Academy of Sciences.

Defination from the web:
... Hemiptera, known as giant water bugs or colloquially as toe-biters, electric-light bugs and Alligator Ticks (in ... Pictures of a Giant Water bug from whatsthatbug.com. Lethocerus, Abedus, Belostoma spp. on the UF / IFAS Featured Creatures Web site. Giant Water Bug Feeding on Frog ...