Backswimmers
Here’s another couple of bugs that were caught in the little pond in the woods behind our house on April 22, 2012. Sam caught them in the same sweep of the net that turned up the Water Scorpion from last week. They were pretty visible as they squirmed and hopped around inside the net. And once I got them back to the house and into a little dish of water, they started backstroking around vigorously
These are Backswimmers, in the family Notonectidae. They are pretty distinctive, because they swim around upside down with their feet pointing up.
They aren’t obligated to swim, and in fact these specimens seemed more than happy to drag themselves out of the water.
Once out of the water, we see that it has a nearly white back[1]. This sure looks to me like the species Notonecta lunata, as none of the other species shown are quite as white on the back, or have such red eyes.
The belly side, on the other hand, is so dark as to be almost black.
This is almost exactly the opposite of what we are used to seeing. It is much more common to see animals that have dark backs and light-colored bellies, on everything ranging from deer to mice to fish. That’s generally because they are using countershading and background matching as an aid to camouflage[2]. But actually, the backswimmer is using countershading too. It’s just that it swims flipped over, so the part that needs to be pale-shaded is its back instead of its belly.
These kept climbing out of the water, possibly because the dish we had them in was too small to suit them, and contained no prey for them to catch. They seemed to like to perch on a rock, possibly to dry out their wings in preparation for flying off to find a better location.
They look pretty similar to Water Boatmen as far as body shape and swimming style, but they have a very different diet. While water boatmen mostly eat algae, Backswimmers are predatory, and they can bite. They’ve got a strong, stout proboscis, with a sharp point at the end for penetrating flesh.
While they have trouble walking on land, they aren’t completely helpless. They can use those long rowing legs to jump quite a long way – four or five inches. Which is far enough to make them hard to catch with one’s bare hands.
———–
[1] There’s just something about the second photo that strikes me as being something that would look good on a coffee mug. So, I went ahead and made one for myself on Zazzle. Then I figured, hey, maybe somebody else would like them, too. So I created a Zazzle store, and posted it for sale.
I just got mine Monday, and it looks good. I’m not doing this with any expectation of making any significant amount of money, but if five or six people buy mugs, then it will pay for mine 🙂 (and, of course, I certainly wouldn’t object to making a bit of money . . .)
[2] There are two reasons for being dark on top and light on the bottom. Countershading is mainly used to hide the shadow that the upper parts of an animal or camouflaged object casts on the lower part. Basically, a white belly in shadow, is about the same color as a gray back exposed to light. The picture below was done by camouflage pioneer Abbott Thayer to show how effective this is: there are supposed to be two camouflage-painted wooden ducks in this picture, one with countershading and one without.
Personally, I can’t see the countershaded one at all! (and I’m not entirely sure that Thayer wasn’t just having a bit of fun, and there isn’t actually a second duck present. All I can make out is what looks like part of a second wire ring that would be its stand, but that’s about it).
Countershading is mostly effective for hiding from viewers looking at you more or less from the side. The other effect, “background matching”, is important for hiding from viewers above and below you. Deep water and ground tend to look dark, while the sky tends to be light. So if you are swimming in, say, a pond, if your upper surface is dark, then you will blend in with the dark bottom to any viewer above you. But if your bottom surface is light, then you will blend in with the bright sky to any viewer below you. So when you combine this with the countershading effect that hides you from viewers to the side, it is just all-round useful to be dark on top and light on the bottom. This doesn’t just work on animals, it is also used in a lot of military camouflage, particularly on aircraft.
Comments are closed.
I learned something new today – the countershading concept. As for the mug, this little guy is pretty cool, but dragonflies are better.
🙂
I’ll see if I can find a favorite photo of yours to recommend.
Hmm. This guy is pretty cool (as is the green one from way back when). but the background isn’t conducive to an attractive mug image. Maybe you’ve hit upon something new. Once you’re done shooting the subject for the blog, try taking a shot or two with a white background or other solid color that you can photoshop away.
KT: I may have to do that. Lately I’ve been photographing a lot of things just on a sheet of white paper, and if I make a point of getting at least a few pictures of everything like that, then I can make a whole line of things with insect images. It looks like there are about 20 pictures already posted that have white backgrounds, so that would be a good start.
The dragonflies have just come out in the last week, so now would be a good time to try to get one into a white-box and see what can be done.
That green one you did way back when was gorgeous. Like a flying jewel.
Oh, and you need your URL and blog name on the mug.