| Nepidae | |
|---|---|
 | |
| Nepa cinerea | |
 | |
| Ranatra linearis | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| Class: | Insecta |
| Order: | Hemiptera |
| Suborder: | Heteroptera |
| Infraorder: | Nepomorpha |
| Superfamily: | Nepoidea |
| Family: | Nepidae Latreille 1802 |
| Subfamilies, Genera | |
See text | |
Nepidae is a family of exclusively aquaticHeteropteraninsects in the orderHemiptera.[1] They are commonly calledwater scorpions for their superficial resemblance toscorpions, 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 andRanatrinae. Members of the genusRanatra, the most widespread and species-rich genus, are sometimes calledneedle bugs orwater stick insects as they are slenderer thanNepa.[3]
While water scorpions do not sting with their tail (it is used for breathing),[4] they do have a painful bite (strictly speaking a sting by their pointedproboscis), 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 fromhypersaline lakes andbrackish lagoons,[6] the Australian genusGoondnomdanepa is restricted to flowing waters,[7] andNepa anophthalma is adapted tolife in caves inRomania.[8]
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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 AsianRanatra chinensis and South AmericanR. magna can approach 6 cm (2.4 in).[10][11]
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 asiphon. Air is conducted through it to thetracheae at theapex of the abdomen when the tip of the tube is thrust above the surface of the water (similar to a snorkel).[12][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.[13] In immature forms the siphon is often underdeveloped and respiration takes place through six pairs of abdominal spiracles.[12][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.[14]
Their frontal legs are modified into raptorial appendages that are used to grab their prey. They feed primarily on aquatic invertebrates such as other insects, but occasionally take small fish or tadpoles. 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.[3]
Nepidae has around 250 species in 14genera divided into twosubfamilies, Nepinae and Ranatrinae.[3][10]
Among these the most diverse are the widespreadRanatra (about 100 species)[10] andLaccotrephes (about 60),[15] but the family also includes species-poor genera, like theEthiopianBorborophilus,Nepella,Nepitella andParanepa (each with one species),[13] IndianMontonepa (one species), PhilippineBorborophyes (one species),[16] and AustralianAustronepa (one species) andGoondnomdanepa (three species).[17]
Araripenepa from the Early Cretaceous (Aptian)Crato Formation of Brazil is the oldest known member of the family, and is the sister group to remaining genera.[18]
Authority: Douglas & Scott, 1865 (sometimes called "water stick insects")
Genera in this subfamily include:Austronepa andGoondnomdanepa are restricted to Australia.Cercotmetus is from Asia to northern Australia and resemblesRanatra (Worldwide distribution), although the former has a distinctly shorter siphon.[10]
Authority: Latreille, 1802 (sometimes called "water scorpions")
One or more of the preceding sentences incorporates text from a publication now in thepublic domain: Chisholm, Hugh, ed. (1911). "Water-scorpion".Encyclopædia Britannica. Vol. 28 (11th ed.). Cambridge University Press. p. 386.
Media related toNepidae at Wikimedia Commons
Data related toNepidae at Wikispecies