This post is about balls. Of wood. Created by caterpillars. Not what you expected, eh?

The story starts with the species Comachara cadburyi, the eggs and youngsters of which I introduced back in this post. I have not given any updates on them because their development has been fairly uneventful – growing into larger green and white caterpillars, gaining a few more setae along the way.

Finally they were looking prepupal – usually characterized by a slight color change. A few had gained light brown chevron markings, so I put a piece of soft wood into the container (many species in the subfamily Acronictinae burrow into wood to create a pupal chamber and safely pupate).

The next day, this is what I saw:

Uhhhh…. what? Is that really my green caterpillar? The rear end is on the right, the front end is on the left buried in the bark.

Note there was no molt to obtain this color change – it is the same size, the same instar. One individual can change from green to brown in order to become less conspicuous as it spends several hours digging its pupal tunnel.

That’s not all folks! I took a look at the bottom of the branch, and saw another caterpillar digging. But this one wasn’t nearly as brown, in fact it was just the right shade to blend in with the pale pulpy wood it was sitting on.

How crazy is that!? I wonder how a caterpillar can determine the color of the wood it’s sitting on? Caterpillars don’t even have proper eyes, with stemmata instead of the usual compound eyes or ocelli. I was able to watch two burrow into the bark with dark coloration, and two burrow into the pulp with greenish tan coloration.

That’s not the best part, though. This is how it’s done.

Wood balls! And now, in action:

It was fun watching the caterpillars digging and throwing their perfect little balls of wood, sometimes getting flung as far as 6″ away.

And finally… the entrance all sealed up. Unfortunately I missed the last turn around of this one (they back in so they can seal up the tunnel behind them), but I was able to spot the entrance. Caterpillars have spinnerets in their mouths, and use the silk for a variety of purposes. When they are young they can use the silk as a safety line, before each molt they create a mat of silk to cling to, and when they are ready to pupate the silk comes in handy for securing themselves to a potentially precarious substrate. In this case, it has been used to adhere a piece of bark to the tunnel entrance.

So now I just have to keep an eye out for emerging adults!


Posted on June 21, 2011, in Acronictinae, Comachara, Invertebrates, Lepidoptera, Noctuidae. Bookmark the permalink. 5 Comments.

  1. Balls that’s cool!
    I get foresters flying around my apartment each spring that wandered off from my stock the year before… always wondering what piece of furniture or molding they found that suited them.

  2. I know nothing about caterpillars, a subject I have only a faint interest in, but somehow your blog keeps me coming back.

    How DO they tell the color? I’ve wondered this about other color-changing life forms – some of them don’t even use the same light wavelengths as humans to SEE colors. This made me wonder if your caterpillars are sensing heat reflection with their feet and changing color until their skin matches the same heat reflection… what do you think?

    Ignorant but interested!

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Ryerson Lab

Functional Morphology, Sensory Biology, Behavior, Biomechanics

I spell it nature

Trying to make sense of the world through science and language.

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