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Water Scorpions: Freshwater Species of the Week

Ranatra chinensis water scorpion under water
A Ranatra chinensis water scorpion prowls along the bottom. The aquatic insects hunt for invertebrates and even small fish and tadpoles. Photo: OpenCage, Wikimedia Commons

 

A few weeks ago, I went kayaking in the placid waters of the Potomac River off Washington D.C. After putting in at Jack’s Boathouse in historic Georgetown, a few dips of the paddle took us to a leafy section of the city that was nearly silent, except for the distant whir of traffic and regular rumblings overhead by jets on a flight path to DCA.

freshwater species of the weekAfter paddling for a while we passed a canoe steered by a middle-aged woman and two school-age children. An animal carrier the size of a small dog rested in the middle of their craft, empty. Along the bank, two female mallard ducks squawked, wrestled, and pecked at each other, a splashing, tumbling ball of motion that was clearly upsetting the rest of the small flock.

“We just released our ducks, and it is causing some tension,” the woman told us, slightly embarrassed. “Mom, that’s one of our ducks!” said one of the kids, although not as concerned as one might think.

To escape the drama, we paddled a bit farther. We stopped in a quiet alcove to rest a minute. A kingfisher rattled off its distinctive, almost manic call in the thick canopy along the river bank. We watched for a while as it flitted from tree to tree, inspecting the slowly moving current. We hoped to see a splashdown, but it moved on.

We rested our boats along a large fallen tree that sunk into the brown water. Carpenter ant scouts were soon patrolling our craft, investigating this new flotsam. We gazed into the cool water and caught sight of a curious critter, a large, twig-thin insect resembling a walking stick.

Discovering a Water Scorpion

We lifted it out of the water with a paddle, examining the two long tubes that extended far off its rear end. The insect waited patiently, motionless, while we examined it. With a dip of the paddle it was back under the log, hiding in the shadows.

When I got home I did a little Googling, and found out that I had discovered a water scorpion (sometimes written waterscorpion), a member of the Hemiptera or “true bug” order that spends its life in the water. Water scorpions make up the family Nepidae. (Not to be confused with giant sea scorpions.)

The water bugs aren’t closely related to scorpions, though they superficially resemble them because their front legs are modified into grappling limbs and they seem to have tails, which are actually snorkels that they stick above water to breathe air.

Ranatra chinensis water scorpion diagram
Ranatra chinensis, a common water scorpion and probably the one I saw. Wikimedia Commons

 

Water scorpions are found almost everywhere there’s freshwater except Antarctica, yet they aren’t often observed. They mostly eat other invertebrates, but have been known to take tadpoles and minnows. Females lay their eggs in the mud or decaying vegetation above the water line.

AKA Water Stick Insects

I had seen a member of the genus Ranatra, the most widespread and biggest group of water scorpions. These are sometimes called water stick insects or needle bugs, and they can reach up to five inches in length.

When a Ranatra gets ahold of its prey, it pierces it with its sharp beak and injects saliva, which sedates and starts to digest their quarry. Their eggs take two to four weeks to hatch, and young mature in about two months.

Interestingly, one species name, Ranatra fusca, is now used for a creativity award in Odyssey of the Mind, since that insect featured prominently in an early competition.

The water scorpion goes to show that you may have many wonderful things to discover right under your nose.

 

Brian Clark Howard covers the environment for National Geographic. He previously served as an editor for TheDailyGreen.com and E/The Environmental Magazine, and has written for TheAtlantic.com, FastCompany.com, PopularMechanics.com, Yahoo!, MSN, Miller-McCune and elsewhere. He is the co-author of six books, including Geothermal HVACGreen LightingBuild Your Own Small Wind Power System, and Rock Your Ugly Christmas Sweater.

Comments

  1. Brian Clark Howard
    August 20, 2012, 9:37 am

    Ha, good one Ima Ryma!

  2. Ima Ryma
    August 11, 2012, 4:10 am

    I am just minding my own biz,
    When suddenly scooped up and out.
    National Geographic tiz
    Wondering what I am about.
    Lucky, I got a greenie guy
    Who in the river let me go,
    Then he went home and googled I,
    A water scorpion, ya know,
    That’s in the order of bug true.
    Oft called needle or stick insect,
    Cuz I look twiggy, yes I do,
    With lots of limbs that all connect.

    I’m right there under N.G.’s nose.
    What the heck, I do my best pose.