Dead Giant Water Bug

2012 March 24

Rosie brought this home from preschool back at the beginning of March, 2012 (just a couple of weeks ago). She said that it was from Mrs. Fezzey (one of her teachers), who knew about this blog and thought I would like it. It was dead of natural causes (and therefore perfectly safe to handle[1]), fully intact, and very nice.

This is another Giant Water Bug, like the one that I posted back in 2009[2]. It was just about 2.5 inches long.

Mrs. Fezzey told us that she found it on the beach at Rabbit Bay, on Lake Superior. The thing is, she found it the first week of March. I expect it had been washed up on the beach during the windstorm of February 29! For reference, the Lake Superior beaches are normally still frozen solid at that time of year. Yes, the winter of 2011-2012 has been an oddly warm winter locally.

Anyway, since this one was dead (but still moist and flexible), I was able to get a lot of detail pictures that I didn’t get with the 2009 specimen. Here we see a closeup of the breathing straps at the tip of its abdomen. Giant water bugs breathe air, and they use those short strap-like appendages to break through the surface film of the water and open a channel so that they can suck air underneath their wings. They can then swim underwater for extended periods without drowning.

The air bubble is somewhat like a scuba-diver’s air tank, but it also has a “gill” effect: the surface of the bubble can exchange gases with the surrounding water, so carbon dioxide can diffuse out of the bubble, while oxygen can diffuse in. There is more gas dissolving from the bubble than coming in from the water, so the bubble does shrink over time and need replenishing, but it still lasts longer than an equal volume of air would last without the gas exchange with the water.

The front grabbing legs have a distinguishing feature that can be used for species identification: the fat part of the leg (the femur) has a groove in it. If I understand the identification features listed on BugGuide correctly, this groove is characteristic of the common species Lethocerus americanus.

The thinner part of the leg (the tibia) sockets into this groove, so that the bug can stow its grabbing legs neatly when not in use.

From the side, we can see that the bug is highly flattened, which camouflages it pretty well as a dead leaf. All the better to ambush hapless fishes and tadpoles that don’t pay sufficient attention.

The underside of the abdomen is distinctly segmented, and there appears to be a keel structure running down the middle. This might be to help the bug swim straighter.

The mouthparts aren’t very pronounced, but they don’t need to be. Once it has hold of its prey with those front grasping legs, it can drive in its proboscis to inject toxic digestive fluids. Once the prey’s insides are liquefied, it can just suck them up.

The rear four legs are flattened with a fringe of hairs, so that they can be used like oars for swimming. Giant water bugs aren’t particularly strong swimmers, they prefer to just hang onto submerged objects and lunge at small animals as they swim past. So while they can use those legs for swimming, they are used more for just hanging on.

All of the legs have sharp, pointed claws that can be stabbed into things to hold on. The grabbing legs, and the middle pair of legs, all seem to have only a single claw. But a closer look at the rearmost pair of legs appears to show two claws, right next to each other.

So, there we are. A close look at one of the largest insects in North America. I tried to open up the wings, but there seems to be some sort of locking mechanism holding them down. These bugs can certainly fly, but evidently one only gets to see the wings if the bug decides to let you. And, being dead, this one wasn’t in any condition to let anyone do anything.

[1] Although, I understand that sometimes giant water bugs will “play dead” when first found, and can suddenly “come alive” and grab you. So it is best to be a bit cautious about them at first. This one, though, was not merely dead, but really most sincerely dead.

[2] That previous bug was kept in an aquarium for part of the summer, and we fed it feeder goldfish that we bought for 29 cents each from WalMart. The thing is, sometimes it would miss a goldfish, and the fish would then be more cautious and impossible for it to catch. There were two goldfish that got wise to it, and so when we released the bug into a nearby pond, we still had these survivors. So now, here it is three years later, and we still have those two fish. They are doing fine, and are now big enough that I’m not so sure a water bug could eat them.

9 Responses
  1. JennyW permalink
    March 25, 2012

    A font of information! Thank you! I loved your nod to the Wizard of Oz. 😉

  2. March 26, 2012

    Very interesting post. Do you know anything about those “toxic digestive fluids”? Are they similar to gastrointestinal fluids in human beings? Or are you not into chyme type investigations?

  3. March 26, 2012

    JennyW: You’re welcome. I always loved the little coroner in the Wizard of Oz.

    Julie Ali: I found the following paper that reviews the predatory arthropods that use “extraoral digestion” to feed (liquefying their prey’s insides so they can suck it up):

    Cohen, Allan Carson (1995) “EXTRA-ORAL DIGESTION IN PREDACEOUS TERRESTRIAL ARTHROPODA”, Annual Reviews of Entomology, Vol. 40, pp. 85-103

    From the section discussing true bugs (which includes the giant water bugs), it sounds like they probably don’t inject venoms as such (where I’m taking “venom” to be a substance that kills quickly without much affecting the structure of the prey). They inject proteolytic enzymes, acids, and other digestive fluids, and the dissolution of the prey’s flesh is what kills it.

  4. March 27, 2012

    Awesome job as usual, Tim! What’s with the eyes? They don’t look like normal bug eyes. Are they optically more complicated?

  5. March 28, 2012

    KT: I’m kind of surprised by the eyes, too. There’s no sign of facets at this resolution. Either they have unbelievably tiny eye facets (and therefore extremely good resolution), or there is a clear protective bubble over the eye surface that makes it impossible to see the facets. I really need to get it under a microscope to check.

  6. Paul permalink
    April 20, 2012

    We live in central MA and my dog was barking at this thing on the driveway underneath one of our lanterns. So I pick the thing up in a jar and start scouring the web. Low and behold, my giant cockroach with Schwarzenegger arms turns out to be a giant water bug. Based on the front arms alone, I knew it probably had an ugly bite, hence the jar (I usually just pick big bugs up by the back). What a freaky beast! Great job documenting your initial find, as well as your “Really, most sincerely dead” GWB corpse! This toe biter may get bitten by my toe, however, or perhaps sauteed with some fava beans and a nice Chianti…..

  7. jeric permalink
    November 27, 2012

    do they have multiple lenses in there eyes?

  8. November 28, 2012

    Jeric: Yes, they do. The individual facets of the eyes are just small enough that we can’t quite see them in these pictures.

  9. Deniz permalink
    March 7, 2014

    I’m modelling a water bug, and these photos were very helpful! Thank you.

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