My Favorite Aquatic Insect

Water scorpion

Water scorpion, Family Nepidae, Ranatra quadridentata

I was planning to do another post in my water quality series, but I am not feeling it tonight.  Instead, I am going to discuss my favorite insect, Ranatra quadridentata.  You don’t mind, right?  We’ll get back to the water quality stuff next week.

I got excited about the possibility of pursuing entomology as a career because of dragonflies.  I adore dragonflies and love everything about them.  They were my favorite insects for a long time.  But then I went out collecting with a friend a semester or two after I moved to Arizona.  We were looking for giant water bugs for my research and mucking about in a stream.  Our strainers flashed through the little pools that had formed in the streambed during the dry season and came up full of treasures.   I hadn’t taught my first aquatic entomology course yet, so I didn’t yet know most of what I was looking at.  At one point, I was shifting the leaves, sticks, and other non-insect junk around in my strainer and pulled a stick out.  I was just about to toss it back into the pool when it moved unexpectedly!  I may have been a wee bit startled.  I jumped badly and the contents of my strainer ended up in my lap, the “stick” back in the water.  I scooped it back out and took a closer look.  My first Ranatra quadridentata!  From this improbable beginning, my love affair with the water scorpions began.

Respiratory siphon

Respiratory siphon

Water scorpions belong to the true bug family Nepidae, which is very closely related to the giant water bugs in the family Belostomatidae.  Although the species in the genus Ranatra are long and narrow (they are commonly called water sticks), those in other genera, such as the genus Nepa, look a lot like the larger giant water bugs in the genus Lethocerus.  It’s easy to see how closely related they are just by looking at them.  They are both predators, both large aquatic insects, and they both have respiratory tubes that extend off the back end of the bugs.  The easiest way to tell the two families apart is by looking at the respiratory siphon: giant water bugs can retract theirs into their bodies while the water scorpions cannot.

Some of the water scorpions are big, impressive bugs.  But I don’t love those.  In fact, I haven’t ever seen a live one.  No, I love the water sticks, the little skinny guys.  They’re all over Arizona and I’ve seen thousands, maybe millions.  They are one of those special aquatic insects that have a pollution tolerance value of 11, right off the top of the chart, so they can live in some of the most disgusting water you can imagine.  They can be incredibly abundant in those kinds of waters because they are able to outcompete nearly everything else that might try to live in there.  At one pond we take our aquatic entomology students to, you might get a hundred water sticks every time you swish your strainer through the water.  Dropping a stick or a rock into the pond results in hundreds or thousands of water scorpions boiling up to the surface.  It’s impressive!  (Wish I had a photo of it…)  The bugs also play dead when you pick them up.  They really look like sticks.

Being able to live in horrifically gross water and playing dead when you pick them up isn’t enough to make someone love them though.  I love the water sticks for two reasons: 1) they are phenomenally cute, and 2) of all the predatory aquatic insects, I think they are the most ill-adapted to life in water.  It doesn’t seem like these bugs should be able to survive at all!  Let me give you some examples.  Let’s start with their raptorial forelegs:

raptorial forelegs

Raptorial forelegs

The water scorpions are predators and have a diet similar to the giant water bugs (other insects, fish, tadpoles, frogs, etc).  Now take a look at the forelegs on the water stick at left.  Just look at how weenie those legs are!  Most predatory insects have big bulky forelegs (think giant water bugs or mantids) that allow them to strike quickly and powerfully.  Water sticks don’t have those broad, muscular forelegs, so they are slow and comparatively weak.  I’ve never seen them eat anything bigger than a small mealworm and though there are plenty of small things they can eat in the wild, they are pretty pathetic as far as predators go.  At least they have a decent beak for piercing and sucking their food once they manage to get a hold of something:

Piercing-sucking mouthpart

Piercing-sucking mouthpart

Next, they really depend on their breathing tube to survive.  They are very narrow and have very little space under their wings, so they need to stay in contact with the surface most of the time to be able to breathe.  While this allows them to live in some of those very dirty habitats (i.e they don’t need to extract oxygen from the water), it means they can’t stay completely underwater long.  And they call themselves aquatic insects!  Sad…

Then there’s those skinny little legs:

Skinny legs

Skinny legs

Just look at those!  Most aquatic true bugs have broad, flat legs that allow them to swim through the water efficiently.  Not the water sticks!  They’ve got long, terribly skinny legs instead.  That’s not ideal if you are an aquatic insect.  Because they stay near the surface, these bugs are usually latched onto the bank or a rock or some other solid object and don’t need to swim much.  But, they are aquatic and things want to eat them, so they do occasionally need to dive.  It’s hilarious to watch these guys try to swim:

Just look at all the flailing!  And how slowly they move!  It looks more like they flounder about and hope they end up where they want to go rather than actually swimming.  Worst.  Swimmers.  Ever!

So, water sticks are predators with wimpy forelegs, aquatic insects that can’t breathe underwater, and they live in water but can barely swim.  In spite of these shortcomings, water sticks are incredibly abundant, so they’re obviously managing somehow.  You have to love any animal that clings to life the way a water stick does!  And I do.  I really do!  Hopefully you love them just a little bit now too.  :)

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7 thoughts on “My Favorite Aquatic Insect

    • Which one was it who was bitten? I couldn’t ever figure out which one was actually your boss at that job! I have not been bitten, but I imagine they’re painful, just like the water bugs and all of those other little nasty biting hemipterans that like to get trapped where you can’t see them in seine nets. Think D still has his scar from the naucorid? “See this scar? Got bitten by a naucorid.” Must have heard that about a hundred times! :)

  1. I had to let you know I received my gift from your contest today!!! I am so happy! The prints are absolutely beautiful ~ I can’t wait to get new paint on the walls & hang them up. They are a great incentive to get all the repainting & stuff done this summer. As soon as I get them matted, framed & up I will send you pictures! Again, Thank you soooo much!

  2. Another question ~ can you recommend a good field guide to identifying various insects? I spend so much time outside, and am constantly observing the various insects around here, but most of the time can’t identify what I’m looking at, other than a generalization, i.e. “dragonfly”… I want to know more about who I’m sharing this farm with! lol Also would like to know more about the various insects I see in & around the lake below our house, and what they indicate about the conditions…

    • Sure! My favorite field guide for insects that live on land is the Kaufman Field Guide to Insects of North America (http://www.amazon.com/Kaufman-Field-Insects-America-Guides/dp/0618153101/ref=sr_1_1?ie=UTF8&qid=1305611301&sr=8-1). It’s written by a guy I know (Eric Eaton) and he really knows his stuff! It’s where I go when I want to look something up quickly and I think it’s the best field guide. For the things in the lake, I recommend A Guide to Common Freshwater Invertebrates of North America by J. Reese Voshell Jr. It will only get you down to family, but the illustrations are quite good. And, if you happen to get photos of anything you see, you can submit them to BugGuide.net and have them IDed. It’s an awesome, awesome website that’s run entirely by volunteers who love insects. They’ve also got pictures of tons and tons of species that you can browse, though it helps if you can at least narrow it down to a family before you try doing it.

      As for what the insects in your lake say about the water quality… That’s a little more complex because you really need to ID things down to at least genus to get an accurate idea based on the insects. For the most part, however, the EPT species are the best indicators of good water quality (Ephemeroptera/Plecoptera/Trichoptera or the mayflies/stoneflies/caddisflies). There are mayflies and caddisflies that live in lakes, but you probably won’t find stoneflies there because they are flowing water insects. Dragonflies aren’t a really great indicator, but if there are several different kinds of nymphs living in the water then the water’s probably pretty good. A high diversity of species is usually a good sign whereas having only one or two very dominant species is often a bad sign. What’s really bad is seeing lots of fly larvae. If you get a lot of flies and little of anything else, then you’ve got some problems with the water quality. Another thing that can say a lot about a lake’s water quality is the amount of vegetation and algae supported by the lake. If there are lots of plants growing in the water (not just along the shores, but out further into the lake), that’s usually a sign that there are a whole lot of nutrients in the lake, i.e. organic pollution from fertilizers and other sources. If the water is green or yellowish during the summer, you are getting algae blooms and they’re usually caused by nutrient rich water as well. The whole water quality issue is very complex and is a little hard to characterize without some serious water and invertebrate sampling, but these are some general trends. Hope that helps!

  3. Pingback: Insects and Plants Use the Same Strategy for Breathing Underwater | The Dragonfly Woman

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