Nepa – a plain-colored but rare hemipteran gem

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Two nymphs of Nepa apiculata (Kennebunk, ME)

I gently scooped the small brown shape out of the water. At first I thought I had grabbed the wrong object–wasn’t this just a bit of decaying leaf? But then slender legs extended, eyes became visible, and I could make out its true colors. This “bit of old muck” was in fact one of North America’s rarest species in the family Nepidae, the water scorpions. The name is a bit inaccurate, as these are not scorpions at all, but really true bugs (Hemiptera) much more closely related to giant water bugs and stink bugs. Water scorpions are aquatic predators, using a long breathing tube on the ends of their abdomens for gas exchange and large raptorial (grabbing) forelegs for snatching prey. There are only about 13 species in the U.S. and 10 of those are in one common, widespread genus, Ranatra, the members of which are so thin as to resemble walkingsticks. Another two species are in the genus Curicta, restricted to a few localities in Texas and Arizona. The final species, Nepa apiculata, was the one I had just found. It is widely distributed in the eastern U.S. but is rather uncommonly seen, as evidenced by the paucity of photos on BugGuide and other websites. Strangely enough, Nepa is the most common water scorpion genus in Europe, whereas Ranatra is rare.

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The adult Nepa

Nepa apiculata is a rather awkward little animal that seems, at least to me, to be ill suited to its own lifestyle (but they continue to exist, so they must be doing something right). They are not good swimmers and if placed in a jar of water without something to climb up to acquire air from the surface, will soon drown (as I found out the hard way). Thus they seem restricted to very shallow water with lots of vegetation. The locality where I saw my first Nepa, and in fact the only place I’ve ever found them, is a large pond with extensive shallows. I had been visiting this pond for several years and never come across them, but after finding my first one I was alerted to their presence and later found them again in the same spot a few times. I found adults to be a bit more mobile and active than nymphs, but I never had them try to attack small insects I tried to feed to them. Adults have wings but are apparently loathe to use them–I certainly saw no evidence that they were willing to fly. I found them to be rather comical animals, with their funny little heads and their fierce looking forelimbs which they did not even want to use.

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Nepa face. Note the raptorial forelegs and the rostrum (beak) used for sucking the insides out of prey.