Sometimes, things are not always as they appear. The glob on this twig looks like a bird dropping. It is not. It is the camouflaged caterpillar of the giant swallowtail butterfly. This particular caterpillar is about 2 inches long and will soon pupate. Within a few of weeks, I should have a giant swallowtail butterfly soaring around the prairie and sipping on nectar from the prairie flowers.
The caterpillar has been feeding on the leaves of my Hercules Club sapling, Zanthoxylum clava-herculis, for a couple of weeks. In the photo below, the caterpillar is on the main stem just below the lower branches.
Hercules Club is a medium sized tree with spiny branches. I also have the closely related Toothache Tree, Zanthoxylum hirsutum. Both trees look the same to me. I assume I have both varieties, but it is always possible that one or both of the plants were mislabeled at the native plant sales. Both trees are hosts to the giant swallowtail butterfly larva and both trees will numb your mouth if you chew on the leaves are bark, hence the name Toothache tree.
It's true that sometimes, things are not always as they appear. Other times, things are exactly as they appear. This glob in my bird bath looks like a bird dropping. It is.
06-10-10 UPDATE: The caterpillar is gone. I hope it found a safe place to pupate and transform into a butterfly. Wasps get many of my caterpillars once they are plump and juicy.