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.

First, let’s take a look at the picture our reader sent.

As you can see, it’s a great photo that shows the creature our reader found very clearly. So, it is not for a lack of information that we’re having trouble with this reader’s question. Rather, it is the fact that there are so many different caterpillars in the world, which makes identifying them extremely difficult, as we’ve said many times before. They are ridiculously diverse – they are found all over the world (in hot, cold, dry, and moist climates), and they come in all shapes, sizes, and colors. This makes them fascinating creatures, to be sure, but also frustrating from the standpoint of trying to figure out which caterpillars are which.

Moreover, caterpillars are merely the larval form of butterflies and moths, so the immature form of the insect (the caterpillar) looks very different from the mature form of the insect (the moth or butterfly). When you consider that there are nearly 175,000 different types of butterflies and moths in the world (i.e., there are 175,000 distinct species in the Lepidoptera order, to be more scientifically precise), you begin to see why it is so difficult to identify caterpillars. Unfortunately, we must answer the present question as we have answered a few other caterpillar-identification questions before: we simply don’t know what our reader found, and this is true even after we looked through several caterpillar identification guides online and searched through dozens (if not hundreds) of pictures. Alas, this is just the way caterpillar identification goes.

However, this site is read by people from all over the world, and our audience can periodically help us identify creatures we are struggling with. So, if any of our readers have found a caterpillar like the one above, please leave us a comment below. Even if you can’t identify it, you might add a little more information about it, like where it was found and how big it is. Over time, perhaps we’ll unearth an answer.