Please refer also to the following link for details on this group:
Nepidae = Link 1
These are the water scorpions, their superficial resemblance to a scorpion, which is due to the raptorial forelegs and the presence of a long slender process at the posterior end of the abdomen, simulating a tail. There are 14 genera in in two subfamilies, Nepinae and Ranatrinae. Species of the genus Ranatra are referred to as needle bugs or water sticks because they are thinner than Nepa and its allied genera.
All species are predaceous aquatic bugs with raptorial front legs. They have a long caudal breathing tube that is derived from their cerci. This tube is often as long as the body, and is held at the surface as the insect crawls over aquatic vegetation They move quietly and feed on small aquatic animals. They may inflict painful bites on humans. They do not usually fly although wings are funcitonal. The eggs are laid in the tissues of aquatic plants.
Waterscorpions feed mainly on invertebrates, but sometimes will even consume small fish or tadpoles. Respiration in the adult is through the caudal process, which consists of a pair of half-tubes that are locked together to form a siphon. In immature forms the siphon is undeveloped and breathing takes place through six pairs of abdominal spiracles.
The eggs, which are laid above the waterline in mud, decomposing vegetation, the stems of plants or rotting wood, are supplied with air by filamentous processes which vary in number among the genera.
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Lansbury, I., T.E. Woodward (1974). "A new genus of Nepidae from Australia with a revised classification of the family (Hemiptera: Heteroptera)". Australian Journal of Entomology 13 (3): 219–227.
Wright, J. 1997. Water Scorpions Northern State University, South Dakota. Thesis.