Another member of the Hemipterans or “true bugs"is Nepa! Nepa is a member of the family Nepidae, which includes the “Water Scorpions” and are best known for their two representatives Nepa and Ranatra. Water scorpions are related to Lethocerus (and Belostomatidae in general) and are quite similar in appearance and habitat.
Nepids have earned the title of “water scorpion” because of their notable abdominal snorkel which loosely resembles the tail of a scorpion. Unlike their arachnid “counterparts”, this “tail” is completely harmless to humans and is used to intake atmospheric oxygen while the insect is submerged under water. Another feature that relates them to scorpions is their large raptorial claws, which (again) loosely resemble pincers.
Though the claws and pincers differ somewhat in appearance, in functionality they are quite similar. Nepidae are ambush sit-and-wait predators, and despite being aquatic, are clumsy swimmers. So, to circumvent this, they cling to anchors in the water (this can be anything solid; plants, litter, branches etc) and simply wait until something smaller than them swims close enough. Upon this, they snatch their prey with their claws, and use their piercing mouthparts to subdue, and consume their meal.
Nepa is of moderate pollution tolerance, ranking a 6.3/10 on the NCBI list. Since they do not absorb oxygen from the water, they are less influenced by pollutants.
Nepa can be found in slower or still bodies of water like lakes or ponds, typically in shallower sections of the water body. Again, they are poor swimmers, and rely on clinging and climbing to navigate, so they need to be in areas shallow enough to have vegetation to hide and hunt in. Nepids in general are masters of disguise, their coloration is typically drab, and resembles decaying organic matter. Body shapes range from slim and mantis-like (Ranatra for example looks like pine needles) to larger and more broad (Nepa is generally leaf shaped). These camouflage techniques help them go unnoticed by prey and other predators (their uncanny ability to be motionless is also helpful).
Functionally in ecosystems, they can be water quality indicators, and as predators serve as vital mechanisms for population control. I have read from individuals who keep Nepids as pets that they have a favor for Culicid larvae (Culicidae are mosquitoes!). So we can all cheer to know that their favorite snack is one of our greatest foes.
https://www.tn.gov/content/dam/tn/environment/water/policy-and-guidance/DWR-PAS-P-01-Quality_System_SOP_for_Macroinvertebrate_Stream_Surveys-122821.pdf , see page 220 for Hemipteran NCBI scores
Ranatra, courtesy of INaturalist
Nepa also courtesy of INaturalist