Predatory Water Bug Nymph, with Water Mites

2015 March 18

I caught a couple of these with a net out of the pond back in the woods on July 11, 2014. They were clearly nymphs of some type of predatory water bug, and I decided to keep one to see if I could raise it to adulthood.

I had hopes that it would turn out to be a nymph of one of the Really Giant Water Bugs in the genus Lethocerus, like the ones I’ve photographed as adults before, but the way that it holds its forelegs is all wrong.

I kept it in a little half-pint canning jar about half-full of water, with a screen lid, and fed it a fly every day or two. This seemed to work out OK, and after about 10 days it molted, leaving this skin. For size reference, the thing the molted skin is laying on is the tip of a standard dinner spoon.

That little reddish-brown thing at the tip of the abdomen is a parasitic water mite. When the water bug molted, it evidently sloughed off its parasites as well, and when I changed its water immediately afterwards all of the mites were cleared out. Here’s a closeup of one of the mites:

Things were going swimmingly with the bug, it grew well and molted twice, until I made a mistake. I took one of the deer flies that had been caught on my Tanglefoot Hat, and fed it to the water bug. And the next day, the water bug was dead. There was just a little bit of tanglefoot on the fly’s wings, and I think that some component of it (maybe the castor oil?[1]) is very toxic to insects. I wasn’t expecting that, since the container didn’t say anything about it having any pesticidal properties. Then again, I suppose it’s possible that deer flies are toxic themselves.

At any rate, by the time it died the bug was big enough to narrow it down to genus. While it isn’t one of the GIANT giant water bugs in the genus Lethocerus, it does appear to be one of merely giant water bugs in the genus Belostoma.

The legs are held in more of a “praying mantis” position, rather than sweeping in to grab prey from the sides.

These evidently overwinter as adults, and are among the species where the female glues her eggs to the male’s back to incubate them. So, now that I know that these are in the pond back there, I think the ideal time to troll a net for the adults would be in the spring, right about the time the tree frogs start singing.

[1] Looking into this, it turns out that castor oil can contain Ricin. On the one hand, ricin is a fairly fragile protein that is normally destroyed during the castor oil extraction process. On the other hand, it is crazily toxic (at least to humans). So it isn’t much of a surprise that a bit of castor oil in the water might kill an insect like a water bug.

2 Responses
  1. March 18, 2015

    Too bad the little beast didn’t live longer. It looks like the inspiration for an interstellar craft in a SciFi movie.

  2. Barb quenzi permalink
    March 20, 2015

    Amazing how you can keep these creatures alive and get them to molt for you.

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