Large Sphinx Caterpillar

2013 December 21

I found this large caterpillar on August 31, 2012, crawling across the sidewalk on campus. How large was it? Well, here it is crawling on my thumb:

It’s certainly one of the Sphinx Moths (family Sphingidae), and one of the larger ones at that. It doesn’t have much in the way of distinguishing marks, aside from some stripes on its head,

and a blue-green color on its “horn”.

The lack of marks is actually somewhat diagnostic, as most sphinx caterpillars have some sort of distinctive coloring (stripes and what-not). Although, this one was very close to pupating, and its skin had that kind of baggy appearance they get just before they molt, so the colors may have been off from normal.

I did keep it to try and rear the adult, but unfortunately it needed to overwinter, and didn’t come out in the spring. I’ve had terrible luck rearing sphinx caterpillars, they seem to need fairly specific conditions of humidity in order to get through the winter.

Anyway, I think the most likely candidate is the Great Ash Spinx, Sphinx chersis, which has the blue horn, and elongated black breathing spiracles rimmed with white, like this one does. And also the caterpillars come in a range of colors, from pinkish to green, so this one falls in the color range. It even has the seven diagonal white lines on its side, although they are pretty faint. I haven’t gotten a picture of one of the adults yet, though (and Bug Guide doesn’t show any of them having been photographed in Michigan yet). In spite of the name, they don’t only eat ash leaves, they are also found eating plum and quaking aspen. And they will eat lilac and privet in the laboratory, although it’s not clear that anyone has found them eating those plants in the wild. Personally, I’m inclined to doubt that they like the lilac much – nothing local seems to be that fond of eating lilac.

Another possibility is the “Waved Sphinx”, Ceratomia undulosa, which has fairly variable caterpillars that sometimes look like this, and its caterpillars are frequently confused with the Great Ash Spinx caterpillars. And I’ve photographed an adult Waved Sphinx in the past, so we know they are around here.

3 Responses
  1. December 21, 2013

    I believe this caterpillar was parasitized. Those random black spots (e.g. between the horn and one of the spiracles in your fourth photo) usually indicate that some sort of parasite emerged (the exit wound). It probably was too compromised to complete metamorphasis.

  2. December 22, 2013

    First thought: a mindless eating machine.

    Excellent photos, as always!

  3. December 23, 2013

    Troy: I think you’re right. The dark spot just behind the head, and the one that you pointed out, do look a lot like the discolorations I’ve seen on other parasitized caterpillars. It’s certainly very suspicious.

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