Marsh Treader

2012 September 15

We made another expedition to the pond in the woods behind the house on May 2, 2012[1], and caught some more interesting things. One of them was this spindly little specimen, that was standing on the bottom of the water in our tadpole pail. It was only a bit over a centimeter long, and so thin as to be practically impossible to see.

When I first saw it, it was standing fully submerged on the bottom of the pail, and seemed content that way, so I assumed that it was fully aquatic and left it there. But then by the next morning, when I was ready to photograph it, it acted as if it had died. After I had fished it out of the water and started photographing it, though, it started to twitch and then gradually sorted out its legs, acting as if it had some intention of getting up. So it looked like (a) it wasn’t actually aquatic, and needed to breathe air at least part of the time, but (b) it could evidently spend some non-trivial amount of time submerged if it had to.

I wasn’t sure what it was at first, but after some poking around it looks to be a “Marsh Treader” or “Water Measurer” in the family Hydrometridae. Specifically, it was probably the only species reported to be found in the northern part of North America, Hydrometra martini. One of their distinctive features is the very elongated head. At first I thought it had a long neck and a little head at the very end, but then I saw where the eyes were located:

So, the whole head is streeetched way out, until it is a large fraction of the length of the whole body. Marsh treaders are predatory, and have an elongated piercing/sucking mouthpart that fits into the underside of that long head. And the bulge at the end of the head is evidently to hold the muscles to control that mouthpart.

While they are predatory, they aren’t very big, so the things that they eat themselves aren’t very big, either. They are a bit like water striders in that they normally walk on the surface of the water, but instead of skating like crazy over open water like the striders do, the marsh treaders tend to walk slowly around in the stagnant, weedy areas. They mostly eat other insects that live in or near the surface film, like springtails, mosquito larvae, midges, and the like.

I don’t know if this one happened to be underwater when we accidentally caught it in the water that we used to fill the bucket, or if it was standing on the surface and got sunk when the water rushed in. In any case, they don’t seem anywhere near as water-repellent as water striders, which are practically unsinkable.

[1] One of Sam’s friends from school wanted to catch tadpoles, so the friend came over with her mother and brother to go back and see what we could see. We eventually did catch a nice big tadpole for her, but it took a while, and we caught a bunch of other things first, like snails and leeches. This one wasn’t even caught intentionally, I was looking at other things in the pail and happened to notice that one of the little bits of decaying grass had spindly little legs.

2 Responses
  1. September 15, 2012

    This has got to be the most emaciated elongated insect I have ever seen.
    It looks like a hippo in terms of its facial features (maybe pulled out like taffy a bit) but the rest of him is so stretched out he looks just as skinny as my younger son. I’m glad you have written out details such as “eyes” and “piercing mouthpart” because for the life of me I can’t see that mouthpart (old age does this to eyesight I believe).

    The bit in front of the mouthpart is interesting as well—it looks like an add-on functionality—a sort of false mouthpart—but maybe it is a skimming detail? Do you see the part I’m yapping about? That two pronged fork thing-a-bob in front of the piercing mouthpart.

    The poor thing looks like he needs a lifeguard to resuscitate him but I guess he recovered without yoru provision of mouth to mouth services.

    When the boys were young and not attached to mechanical devices such as the computer and the X-box, we spent many happy hours at the John Janzen Nature center pond (before they made it into a yuppified piece of outdoor marsh. They fell into the pond many times to get close ups of the tadpoles and we brought several tadpoles home in pails along with disgusting other creatures that the boys –at this special time in their life when they actually favored nature over machines—were interested in. Besides the pond they were given those dollar store nets to catch butterflies and never managed to catch a single flying creature and instead spent most of their time trailing their nets in the glop of the marsh near our home and the aforementioned pond. It is funny but now that such time are gone, I think they were probably the richest times in my sons’ lives. I don’t imagine they think this is so, but certainly they have a great many details of squished water striders, grasshoppers that they chased and never caught, yellow butterflies and pale moths that they mangled in their nets and the entire parade of days that went by like water through the holes of their nets.

    This bug is very sickly and yet, it has served to remind me of those long lost days when the boys were six and two years old and both of them would carry an empty milk carton (to hold their treasures of twig and bug) , a bucket to slosh water and tadpoles, and of course the broken dollar store net.

    I’m glad Sam is experiencing the same sort of childhood as my babies.

  2. September 17, 2012

    Nice camouflage! It looks like a rotting twig.

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