Water Boatman
Water boatmen, like this one, are all over the place. They can fly, so they end up in bodies of water ranging from full-blown lakes, to puddles and birdbaths. This particular one was at the mouth of Cole’s Creek, just down the road from our house.
They look kind of beetle-like, but they are actually in the family Corixidae, which are included in the Heteroptera, or “true bugs”. There are a bunch of species of water boatmen, but it isn’t realistic to try to distinguish them down below the family level, because they all look the same: head with big eyes, streamlined body, and the two hind legs elongated into “oars” for swimming. They aren’t all that fast overall, but when they paddle with those oars, their motions are so jerky, and they are so able to dart off in random directions, that they are somewhat hard to catch[1]
I’m not quite sure what their mouthparts look like. If they are like other true bugs, they would have a “beak” for piercing and sucking, but water boatmen are reported to eat algae and small plankton, which sounds more like the sort of thing that you need to either chew up or lick up. Their front legs are modified to have little scoops on the ends, which look like they are suited for sweeping up tiny floating things in the water:
This is one of the features that distinguishes them from another type of small aquatic bug: the “backswimmers”. Backswimmers are about the same size and shape, and have the same sort of elongated legs with oars on the ends, but (a) backswimmers are predatory, so their front legs are designed for grabbing things and don’t have the little scoops; (b) backswimmers swim upside down, while water boatmen swim right side up; and (c) backswimmers can bite you if they are handled roughly, while water boatmen are harmless. You probably don’t want to use that last item for identification if you can help it, though.
Unlike the other aquatic insects that I’ve found so far, water boatmen actually breathe air. They trap an air bubble under their abdomen and can breathe with this air bubble for some time. If you look at the first picture, you can see the fringe of little hairs sticking out from the back of his abdomen that help to hold the air bubble underneath.
There is a big bonus from breathing air instead of water: oxygen is not very soluble in water, and so even well-aerated water doesn’t supply all that much oxygen. Grabbing an air bubble from the surface not only privides oxygen at much higher concentrations, it also allows the water boatman to live in water that is kind of stagnant and oxygen-poor.
Some species of water boatmen can also make noises, kind of like a cricket, that they can use to call mates through the water. They sound like this.
They aren’t really committed to the whole aquatic lifestyle, this one was perfectly happy to climb up out of the water and onto the side of the dish:
And, somewhat unusually, they can actually fly directly from the surface of the water. In fact, they can evidently shoot up from underwater, pop through the surface, and fly away[2]! This is not something a lot of insects can do, usually they have to haul themselves out of the water before they can spread their wings and fly off. One of the things that lets them do this is that their sufaces are highly water-repellent. The one in the picture above just crawled out of the water a few seconds before the picture was taken, and I can’t see even a single water droplet or moist patch anywhere on it. That’s how completely it shed water.
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[1] We caught this one by quickly sinking a large container right behind it. The sudden inrush of water sucked it right into the container. Voila! I think if we’d tried putting a jar over it, or netting it, it would have gotten away, or at least taken a lot longer to catch.
[2] Like Supercar!
K T Cat:
I loved watching these scoot about on the water when I was a kid!
2 June 2008, 3:09 pmTim Eisele:
K T Cat:
What kind of bait did you use on your hook? I probably would have gone with some kind of nematode.
3 June 2008, 12:43 pm