In polymer chemistry, polymerization is a process of reacting monomer molecules together in a chemical reaction to form polymer chains or three-dimensional networks. There are many forms of polymerization and different systems exist to categorize them.
The thistle caterpillar is the larval stage of the painted lady butterfly. The adult insect migrates into Iowa each year from Texas and Mexico. Eggs are laid on both thistle and soybeans. The caterpillar is easily identified by the spines that resemble Christmas trees that have lost all their needles.
I saw it first on Jerry Coyne's website, then later on Imgur, and then on a crytozoology fact-checking blog called CryptoVille. I have seen a lot of caterpillars with eyespots, but I had never seen this one. This is the caterpillar of a large moth species called the Pink Underwing Moth (Phyllodes imperialis). The best description of the species I could find comes from an Australian Government website.