The water scorpions are distinctive aquatic bugs that possess raptorial forelegs for capturing prey and a breathing siphon extending from the end of the abdomen.
Nepids are poor swimmers and prefer to wait in ambush for their prey with just the siphon extending through the surface of the water. Their prey consists of other aquatic organisms that come into their range, particularly small crustaceans and insects, though they will take tadpoles and small fish if presented with the opportunity.
The raptorial forelegs have an organ that apparently senses the vibrations of the prey, which combines with the use of visual clues to make the Nepidae formidable ambush predators.
, found Australia wide, is the only species in the subfamily Nepinae found in Australia. The subfamily Ranatrinae contains the slimmer, stick-like Nepids and contains 4 genera, 7 species and 1 subspecies. Although distributed across Australia the greatest number of species is found in the tropical north.