8 genera in 2 subfamilies; see text
Notonectidae is a cosmopolitan family of aquatic insects in the order Hemiptera, commonly called backswimmers because they swim upside down. They are all predators, up to nearly 2 cm in size. 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 two subfamilies, Notonectinae and Anisopinae, each containing four genera.
The most common genus of backswimmers is Notonecta - streamlined, deep-bodied bugs up to 16 mm long, green, brown or yellowish in colour. As the common name indicates, these aquatic insects swim on their backs, vigorously paddling with their long, hair-fringed hind legs.
Backswimmers are predators and attack prey as large as tadpoles and small fish, and can inflict a painful "bite" on a human being (actually, similar to a mosquito "bite", it is a stab with their tubular mouthpart). They inhabit still freshwater, e.g. lakes, pools, marshes, and are sometimes found in garden ponds. Although primarily aquatic, they can fly well and so can disperse easily to new habitats.
The Common Backswimmer is Notonecta glauca, widespread in the United Kingdom (where they are known as water boatmen) and Europe. Another species is N. maculata, distinguished by mottled brick-coloured forewings.
In contrast to other aquatic insects that cling to submerged objects, Anisops deanei uses a unique system to stay submerged: using the extra oxygen supply from haemoglobin in their abdomen, instead of using oxygen dissolved in the water. The size of these air bubbles, which provide buoyancy, changes as the nitrogen dissolves into the blood and the oxygen is used in respiration. This allows for regulation of the size of the air bubbles and their concentration of oxygen.
- BBC Science and nature factfiles: Water boatman, common backswimmer Retrieved on 2008-07-26
- physorg.com: Gold Strike in Science World Retrieved on 2008-07-26
- Diving insects use buoyancy vests New Scientist 2006-04-11 p.19 Retrieved on 2008-07-26
- Chinery, M. (1986) Collins Guide to the Insects of Britain & Western Europe. Collins. ISBN 0-00-219137-7.
- Fitter, R. & Manuel, R. (1986) Collins Field Guide to Freshwater Life. Collins. ISBN 0-00-219143-1.
- Hungerford, H. B. (1933) The genus Notonecta of the world. U. Kansas Sci. Bull. 21: 5-195.6+516+2kkig
- Close-up photo by J. Hlasek
- Photo of Anisops assimilis swimming by Paddy Ryan
- BBC Radio special on the sounds made by water boatmen