2 subfamilies: Notonectidae is a cosmopolitan family of aquatic insects in the order Hemiptera, commonly called backswimmers because they swim "upside down" (inverted).

[1] 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.

[2] Backswimmers swim on their backs, vigorously paddling with their long, hair-fringed hind legs and attack prey as large as tadpoles and small fish.

The best-known genus of backswimmers is Notonecta – streamlined, deep-bodied bugs up to 1.6 cm (0.6 in) long, green, brown, or yellowish in colour.

The common backswimmer, N. glauca, is widespread in Europe, including the United Kingdom where it is known as the greater water boatman.