Notonectidae

Notonectidae is a cosmopolitan family of aquatic insects in the order Hemiptera, commonly called backswimmers because they swim "upside down" (inverted). They are all predators and typically range from 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. Their dorsum is convex, lightly colored without cross striations. Their front tarsi are not scoop-shaped and their hind legs are fringed for swimming. There are about 350 species in two subfamilies: Notonectinae with seven genera, and Anisopinae with four genera. Members in the former subfamily are often larger than those in the latter.

Backswimmers swim on their backs, vigorously paddling with their long, hair-fringed hind legs and attack prey as large as tadpoles and small fish. They can inflict a painful "bite" on a human being, actually a stab with their sharp tubular mouthparts (proboscis). They inhabit still freshwater, e.g. lakes, ponds, marshes, and are sometimes found in garden ponds and even swimming pools. Although primarily aquatic, they can fly well and so can disperse easily to new habitats.