Waterscorpions of the genus Ranatra are thin, aquatic, predatory hemipterans in the family Nepidae. The common name “waterscorpion” comes from the specialized raptorial forelegs that superficially resemble the pedipalps (pincers) of scorpions and from the elongate caudal siphon or breathing tube that resembles the sting of a scorpion. Collecting nepids is done relatively easily by sweeping an aquatic net through the vegetation surrounding lakes, streams, and many other sources of slow moving water. Since most nepids are long, thin, and brown, they can be difficult to separate from twigs and aquatic plant material. Waterscorpions feign death when disturbed but can normally be seen moving around in the plant material a few minutes after collecting them. These insects have well developed wings, but they have very rarely been observed in flight. Adults of most New World Ranatra species have a stridulatory mechanism which consists of serrations on the fore coxal cavity that contact coarse ridges of sclerotized setae to produce sound. This particular mechanism is unique among water bugs, and both nymphs and adults of Ranatra possess these structures.

Fabricius described the genus Ranatra in 1790 and Hungerford described Ranatra australis in 1922. In the United States and Canada, 13 species in 3 genera of nepids are described.

The genus Ranatra can be distinguished from the other two Nearctic genera (Nepa and Curicta) by three characters: the anterolateral corners of the pronotum not wider than the head (including eyes); abdominal sterna not subdivided; and the female subgenital plate laterally compressed and keel-like. In addition, the beak only has 3 visible segments and the antennae are shorter than the head. The species Ranata australis is distinguished by the well developed penultimate segment of the antennae and by the lack of an apical tooth or notch on the profemur, as shown below.

Nepids overwinter as adults. Adult females lay eggs in vegetation during the spring months, and the eggs hatch in about 2-4 weeks. Once hatched, the young mature in about two months. Once sexually mature, adults mate at night one floating or emergent vegetation. Nepids use their raptorial front legs to grasp prey. Ranatra species prey on a large variety of organisms, including tadpoles, small fish, and other insects. Like all Hemiptera, they possess piercing sucking mouthparts which they use to stab and inject saliva into their prey which begins extra-oral digestion. Nepids have a breathing tube that is formed from the cerci and is often as long as the body. They extend this siphon just above the surface film while the rest of the body is anchored below the water surface.

Ranatra australis adults live primarily in aquatic vegetation and debris and are often found clinging to vegetation overhanging the water. They occur in a variety of lentic aquatic environments, including grassy margins of roadside ditches, slow moving creeks, and river inlets.

This species is common throughout the southeastern United States. There are 30 specimens in the NCSU Insect Museum from North Carolina (22), Florida (3), South Carolina (2), Minnesota (1), Illinois (1), and Louisiana (1).

1. BugGuide
2. J.H. Epler. 2006. Identification manual for the aquatic and semi-aquatic Heteroptera of Florida. FL Dept. of Environmental Protection, Tallahassee, FL. 186 pp., Link on BugGuide
3. Ranatra on Discover Life
4. 53 images of the genus Ranatra on The Encyclopedia of Life
5. 2 records on GBIF
6. R.W. Sites and Polhemus, J.T. 1994. Nepidae (Hemiptera) of the United States and Canada. Annuals of the Entomological Society of America 87(1): 27-42.