This type of walnut caterpillar comes from a small, very dull-colored and nondescript moth. When these furry monsters drop off the tree and pupate, they transform underground.
My worst tent worm (yet another pest) outbreak on this tree was also when I had laid out a barrier of landscape fabric beneath the tree, in a half-hearted experiment, hoping to interfere in this pupating process. Instead, I think all I did was prevent the armadillos from digging a bunch of pupae up. There were more caterpillars than ever the following season!
Next year, it is war on any caterpillar that sets its sights on my pecan trees, and the armadillos are going to have easy access all year long to did and root around the trees. The trees are too tall for efficient spraying now; biological warfare with bacteria or fungal weapons may also be in order.
After munching on our pecan tree in spring, the walnut caterpillars all simultaneously made their way back down the trunk to shed their old skins. For some reason, they do this as a group; maybe the large furry mass of worms deters predation while a single caterpillar might just look like a snack. Looking like one large furry mammal is much more intimidating. Your guess is as good as mine, but it is quite a sight to see this unusual gathering.
— Artist Susan A. Walton, S. A. Walton Studio, Hudson, Florida