Notonectidae

Family of true bugs

Notonectidae is a cosmopolitan family of aquatic insects in the order Hemiptera, commonly called backswimmers because they swim supine (ventral side up) in a kind of "backstroke". They are all predators and typically range from 0.5 to 1.5 cm (0.2–0.6 in) in length. They are similar in appearance to Corixidae (water boatmen), but can be separated by differences in their dorsal-ventral coloration, front legs, and predatory behavior.

From Wikipedia, under CC BY-SA. More on occurri.