Abbott’s Sphinx Caterpillar
At the end of July, after Sam and I came back from a walk, S_ said, “I have a surprise for you!” and showed us this:
That’s my wrist it is crawling on, by the way. It was just a bit over three inches long. S_ said, “I found it crawling on the porch in front of the house. Isn’t it huge and ugly? I saw it and immediately thought of you!”[1].
Handling it was a bit disturbing. Imagine picking up a raw sausage, and then having it suddenly thrash violently from side to side, and that was about what it was like to pick it up.
It had an interesting feature at the tail end, a structure that kind of resembled an eye. Not an insect eye, but a vertebrate eye:
The size, the color, the lack of hair, and the pseudo-eye on the rear were all pretty distinctive, and it was easy to narrow it down to the Abbott’s Sphinx Moth caterpillar, Sphecodina abbottii. It is a bit different from other sphinx moth caterpillars, which mostly have a horn or spike on the rear. The thing is, the Abbott’s Sphinx changes quite a bit as it grows. They start out green, with a horn on the end segment like other sphinxes. When they are about half-grown, they turn blue-green with an orange knob on the end. Finally, in the last stages before they pupate, they either look like this one, or they turn brown with a set of ten large, pale green “saddles” running down their backs. The larvae eat either grape leaves or virginia creeper leaves[2], and there is some speculation that the color phase with the ten green saddles is adapted to look like a bunch of unripe grapes.
The pseudo-eye makes the tail kind of resemble a snake head viewed in profile. A lot of the things that prey on caterpillars are kind of cautious about snakes, so this could scare off most of the smaller predators. The lashing behavior is pretty darned startling, too, so anything that tries to pick it up and eat it is likely to drop it. Supposedly they also hiss (which is an odd thing for a caterpillar to do), but I didn’t hear any hissing from this one.
An interesting point is that it has evolved a form that mimics a snake in profile, which means that it can get away with simulating only one eye instead of two. But, two pseudo-eyes would be a much more convincing snake mimicry, so why didn’t it go for two? Well, the structure it developed the pseudo-eye from is the “horn” that is characteristic of sphinxes. And, its ancestors only had the one horn. So, they were constrained – if there was only one horn, then they could only fake up one eye. This comes up a lot in evolved systems: a structure gets co-opted for a new purpose, but it is constrained by its starting structure and can’t be formed into exactly what is needed. Instead, it ends up being turned into something that is not perfect, but is good enough. Kind of like the way the human backbone gives a lot of problems, but functions well enough for us to get by most of the time.
Update: I took some additional pictures, including one of the adult that these caterpillars turn into, and posted them on August 2, 2014.
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[1] And then she said, “Whoops, I didn’t mean for it to sound like that”.
[2] This one was probably on virginia creeper, seeing as how we don’t have any significant grape vines around. The virginia creeper (or “five-leaved ivy”) is pretty plentiful on the hill leading down to the swampy area, to the point where it is engulfing and dragging down some of the smaller trees.
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Where in the world would the thing store enough air to hiss?
As for single eyes and spines, a friend of mine says, “Life is a kluge.” I’ve always liked that.
About the hissing: that’s one of the quirks of insects – they don’t actually have lungs, as such. What they have is breathing spiracles, leading to tracheal tubes that branch, and branch, and branch until they conduct oxygen all through the entire body. So, the answer to the question “where would they store enough air to hiss?” would be “Everywhere”. The violent, convulsive side-to-side thrashing of the caterpillar would compress the tracheal tubes on one side of the body, and I can see where it would force the air out fast enough to make an audible hiss.
It would be an aggregate hiss, then, a collection of tiny hisslets all occurring at the same time. Whistling in tune would be impossible for this little guy.
Although, in theory, a whistling caterpillar could whistle *chords*.
I caught one the other day right outside my house in Texas. It is still green and has its horn. It actually squeaks like a mouse. It only squeaked while I was trying to catch it but it scared the crap out of me when it happened.
Zack: That’s pretty cool! Now I need to remember to get a sound recording next time we find a sphinx caterpillar.
I saw a dead caterpillar on the driveway. It was orangish and the eye was not as prominent, but small and almost football shaped. It was quite scary. Maybe nematodes turned it red.
Yergaderga: If you still have it, and are curious, try putting it in a jar and waiting a few weeks. You may get nothing, or you might get some kind of parasitic wasps or flies hatching out!
are they dangerous because i caught one and i think it about to make a cacoon
Shayla: They are a bit startling when they thrash around and hiss, but they are perfectly harmless. And all that the moths do is fly around, drink nectar, mate, and lay eggs.
I found one of these guys in my house on the floor this morning; the thrashing and the one eye sort of freaked me out for a while; took some photos, and let it go into the bushes – we have lots of Virginia Creeper around here, but how it got indoors is a mystery…so very glad it is a harmless moth.
Patricia: I’m surprised it got into the house, too. I knew they wandered quite a bit while looking for a place to pupate, but I wouldn’t expect that.
Maybe it came in through an open window or something.
Was washing my pick up when all of a sudden saw this weird snake looking thing next to the water hose it’s definitely a Abbots Sphinx mouth, I believe it came out of one of my wash buckets I had stored in the garage
As putting it in a jar it was very defensive I still have it any idea what I should do with it?