Please refer also to the following links for details on this group:
Notonectidae = Link 1
This is a large family of aquatic or limnetic insects that are known as "back swimmers" because they swim in a reversed position. They occur worldwide. They are all predators that reach about 2.2 cm. long as adults. 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 body is convex when viewed from the top; the hind legs are long and ore-like but without definite claws. The middle and hind tibiae are fringed with long hairs; ocelli are absent, and they are usually light in color. Their dorsum convex is light 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 Notonecta is streamlined, and can reach 16 mm in length. The color varies from green, to brown or yellow. As the common name suggests, these insects swim on their backs, and paddle with their long, hair-fringed hind legs. Notonecta glauca and Europe and N. maculata are common in Europe.
They attack prey as large as tadpoles and small fish, and can inflict painful wounds on humans. They occur in quiet freshwater such as lakes and marshes. They are good fliers, which enables them to spread rapidly in their environment.. They are considered important predators of mosquitoes in semi-permanent bodies of water and have been manipulated to increase in such habitats through cultural modifications.
Unlike other aquatic insects that adhere to underwater objects one species, Anisops deanei has been found to deploy an interesting system in order to remain submerged: using the oxygen from haemoglobin in the body. 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.
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
Sjogren, R. D. & E. F. Legner. 1989. Survival of the mosquito predator, Notonecta unifasciata [Hemiptera: Notonectidae] embryos at low thermal gradients. Entomophaga 34: 201-08.
Truxal, F. S. 1953. Kansas Univ. Sci. Bull. 35: 1351-23.