Nepidae
Nepidae is a family of exclusively aquatic Heteropteran insects in the order Hemiptera.[1] They are commonly called water scorpions for their superficial resemblance to scorpions, due to their raptorial forelegs and the presence of a long slender process at the posterior end of the abdomen, resembling a tail.[2] There are 14 genera in the family, in two subfamilies, Nepinae and Ranatrinae. Members of the genus Ranatra, the most widespread and species-rich genus, are sometimes called needle bugs or water stick insects as they are slenderer than Nepa.[3]
While water scorpions do not sting with their tail,[4] they do have a painful bite (strictly speaking a sting by their pointed proboscis), but this is much less harmful to humans than a true scorpion's sting.[5]
Nepidae are found on all continents except Antarctica. They mostly inhabit stagnant or slow-moving freshwater habitats like ponds, marshes, canals and streams.[6][7] Exceptionally they have also been recorded from hypersaline lakes and brackish lagoons,[6] the Australian genus Goondnomdanepa is restricted to flowing waters,[7] and Nepa anophthalma is adapted to life in caves in Romania.[8]
Nepidae are brown insects, but some species have a bright red abdomen that can be seen when the wings are open. Their body is broad and flat (subfamily Nepinae) or long and thin (subfamily Ranatrinae). They are rather poor swimmers and typically crawl about on aquatic vegetation.[9] They can fly, but this is infrequently seen.[7] In most species the body is between 1.5 and 4.5 cm (0.6–1.8 in) long,[9] although the largest such as the East Asian Ranatra chinensis and South American R. magna can approach 6 cm (2.4 in).[10][11] Adults of Ranatra australis, which is found in the southern parts of North America, are three to three and a half inches long. [12]
Respiration in the adult is achieved by means of the caudal process, which consists of a pair of half-tubes capable of being locked together to form a siphon. Air is conducted through it to the tracheae at the apex of the abdomen when the tip of the tube is thrust above the surface of the water (similar to a snorkel).[13][3][9] In some species the siphon is longer than the body,[9] but in others it is shorter, in a few even less than one-tenth of the body length.[14] In immature forms the siphon is often underdeveloped and respiration takes place through six pairs of abdominal spiracles.[13][3]
To keep their orientation in the water they have three pairs of “static sense organs”, small oval structures closely associated with the fourth, fifth, and sixth abdominal spiracles.[15]
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