A reader recently sent us a picture of a blue caterpillar with small black spikes on its back and large red spikes on its head. The blue, spiky caterpillar also appears to have two black eyes (even though these are actually not functional eyes, but eyespots, a defense mechanism some caterpillars use to scare away predators). The reader only sent the picture of the spiky, blue caterpillar and this deceptively simple question: “what is this?” Good question.