The shaking caterpillar
Harrisimemna trisignata is an unusual animal. It has so many bizarre adaptations it’s difficult to know where to start. So, I’ll start with some pictures and a video, then give my thoughts. It is in the subfamily Acronictinae (family Noctuidae), which is why I am rearing it.
Harrisimemna trisignata appears to be a bird dropping mimic. Its coloration is beautiful to us, yet probably looks disgusting to a bird. It even looks like it has runny uric acid dropping down the sides of its body. However… it does not sit like a bird dropping mimic. Instead it arches its back, almost reaching its last segment with its head. Every time I look at my caterpillars, they are in that pose. They also have a bizarrely shaped pair of third thoracic legs. Not sure why?
Also, they have a habit of attaching their shed head capsules to the hairs just behind their head. As you can see in the video, they appear to use this head capsule as a mace to ward off attackers. Sometimes these capsules will stack on top of each other in a chain, though they usually fall off and they just have one at a time.
And they shake! They shake when I open the container, when I breathe on them, when I talk to them, when I touch them, when I look at them the wrong way. I can just imagine a potential parasitoid, like a tiny wasp, trying to land on that caterpillar… between the shaking and the head capsule whipping, I doubt it would stick around.
And of course the jumping spider mimic butt. Doesn’t it look like it has a few pairs of eyes on the back? In the last instar (the above photos are second to last) the appearance of a crouched jumping spider is even more dramatic.
They are also ball rollers. When they did their pupal chambers in wood, instead of just chewing up the wood like most caterpillars, they roll it up into neat little balls, then throw them aside. A few genera in the subfamily Acronictinae have this behavior. So far our molecular work has placed them at the base of the tree.
What does this all mean? This caterpillar is a remarkable animal which still has many more surprises in store, I am sure. I am really hoping to rear it again next year to study its behaviors.
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