2007 September 16

Last week, I was out helping S_ drag a body into the woods[1], when she called out, “I just found a really cool looking grasshopper for you . . . hey, it bit me!”
So I said, “Is it green, with really long legs?”


And she replies, “How did you know?”


Well, as it turns out, my reasoning was faulty, even though the conclusion was correct[2]. I was remembering something serendith posted a couple of months back, mentioning that while katydids were mostly herbivorous, they would sometimes eat other insects when they could get them. It seemed to me that an insect that opportunistically ate meat would be more likely to bite than a straight herbivore, so (grasshopperish thing biting somebody) ==> (taste for flesh) ==> (katydid) ==> (green with long legs).


QED, right?

Alas, no. After working through the ID keys for katydids at University of Florida, it turns out that this is one of the genus Scudderia (Scudder’s Bush Katydids), which is in a completely different subfamily than the “red-headed meadow katydid” (Orchelimum erythrocephalum) that serendith was talking about on August 1. I’m not seeing any mention that any of Scudder’s Bush Katydids eat anything other than plant matter. Oh, well. It just goes to show: If you make a wild guess and get it right, then when somebody asks how you know you should just smile mysteriously instead of trying to explain.Anyway, a few anatomical details: this is definitely a female specimen, as is obvious from the ovipositor, which you can see the shape of through the wings here:


The ovipositor is shaped like that (flat and curved) because she lays eggs actually inside leaves. As in, she slides the ovipositor into the edge of a leaf and lays a flat egg between the upper and lower surfaces of the leaf. There is a nice photo sequence showing how she does this at the bottom of this ID page for Scudderia . Of course, anyone going to look at that might say, “But that isn’t the same thing as you are talking about here! That one is *Pink*!” Well, yes. This is a known mutation for katydids, every now and then you get one that is white or hot pink. The pink ones are striking enough that, the first time I mentioned it to someone, the immediate response was that those photos were probably photoshopped. But no, they are evidently real.

Another unusual feature of at least some katydids is that they have visible ears on their front legs:


The ear is just below the “knee”, it is an actual tympanum that picks up air vibrations, just like an eardrum. It makes sense that they would have pretty good ears, considering that the females find males by following their calls.

And, just for good measure, here is a picture of the head showing the “pupil” effect on the compound eyes:


While it looks like the katydid’s eye has a pupil that is looking at the camera, it actually doesn’t. The compound eye is basically a bunch of hundreds of channels with light receptors at the bottom, that look in multiple directions at once. When you look at the eye, you are seeing all the way to the bottom of the ones that are pointed directly at you, so they look black, like a pupil. I’ve seen this pretty frequently in pictures of praying mantids (which are not too distantly related to katydids), but not so much in things like flies.

[1] No, nothing like that. A young deer had been killed by a car right next to our house. It had been there for an unknown amount of time, and was starting to stink, so she dragged it off into the woods for the coyotes and crows while I kept our daughter out of mischief (and the road).

[2] A better chain of reasoning is, grasshoppers look mundane because they are so common, while katydids (at least around here) are scarce enough to look interesting (and hard to spot because of their color). Therefore, (thing that looks kind of like a grasshopper) ==> (unusual enough to remark on) ==> (katydid).

One Response
  1. August 2, 2017

    Thanks for this! I have been having trouble reconciling what I knew about compound eyes with the anthropomorphic way that mantises and katydids always look directly into the camera. For example: https://www.instagram.com/p/BXSoh_hAru4/

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