The Backyard Arthropod Project

They change so much as they grow up!

In the middle of June, S. found this little caterpillar on an aspen tree

The long appendages at the rear were actually a lot more complicated than they look in these pictures. When the caterpillar got annoyed, it would extrude a red tendril out of the end of each one, which it would flail around wildly (unfortunately, I couldn’t get a picture of that behavior). I had to hunt a bit to get a tenative identification on it, and finally found a small inset picture in Caterpillars of Eastern North America[1] that looked enough like it that I figured it was one of the moths referred to as “Prominents”. This one was evidently a very young one (second or possibly first instar), because they change quite a bit as they get older. Unfortuantely, the book only had a picture of the very young form of one of the prominents, which obviously wasn’t the right one, so there was no way to get a good ID on it just then.

Anyway, I put it back on a small aspen sapling near the house, and let it go for 12 days. By the time I looked at it again, it had changed into this:

Quite a change! Aside from being considerably bigger (it was almost 4 cm long last time I looked at it), the little projections on the head were gone, the elongated tails had nested together and become stiffer, the head was hidden under a hump, and the color had changed completely. Now it was possible to make a positive identification, it is either a “Black-Etched Prominent”, Cerura scitiscripta, or a very close relative. It is actually surprisingly hard to spot, it resembles a rolled-up, half-dead leaf, which are very common on aspen trees. Wagner’s book describes how, when disturbed, these caterpillars will rear up, wave their tails, flash a scary “false face”, and ultimately spray acid at you, but this one just wanted to hunker down and play dead leaf [3].

Anyway, I suppose if I wanted to be complete about this, I should have tried to rear it to adulthood and get pictures of it then.

[1] David L. Wagner, Caterpillars of Eastern North America, Princeton University Press, Princeton, NJ, 2005, 512 pages. My aunt recommended this book to us last year, it is very good. Especially since most insect guides kind of gloss over the larval forms, and concentrate on the adults, so you are kind of left out on a limb if you find a caterpillar that isn’t one of the really showy ones. Now, if there was only something like this for just the Great Lakes region[2]

[2] There is a book, Insects of the Great Lakes Region, by Gary A. Dunn, that is pretty specific to our region. It’s published by University of Michigan Press, and it is actually pretty good, except that (a) not all the insects described are illustrated, and (b) the illustrations are all small black-and-white line drawings in the margins. One of the things that made me start on this whole arthropod documentation project was the thought that this book could really use a photographic supplement.

[3] I seem to be pretty lucky as far as not getting sprayed with noxious chemicals by insects. Like the time we found a big, metallic blue beetle down at the Baraga plains, and S. asked me if it was safe to handle. “Oh, sure”, I said, as I looked it over and noticed fluids oozing out of its leg joints. Later, I found out it was a blister beetle (genus Meloe) and that the fluid it was secreting was a blistering agent. Luckily, I didn’t find that out the hard way. That ought to teach me.

Other articles related to this topic:

• Variegated Fritillary Caterpillar
• St. Lawrence Tiger Moth Caterpillar (?)
• Ctenucha virginica caterpillar
• Linden Looper Caterpillar (Inchworm)
• Goldenrod crab spider - female and hatchling