This Week In Zoology: Weirdo Caterpillars

When it comes to extremely odd looking creatures, marine life is usually our best source of inspiration, especially those found in the deep sea. This is partially because the support that water gives allows for more extravagant body plans than land does, and partially because we don’t see marine creatures every day, and so they have not had as much chance to become “normal” to our eyes.

When it comes to terrestrial creatures, however, I think that caterpillars are strong contenders for the “weirdest looking critters” award. This video gives some examples, and many of you might be asking yourselves, WTF are those, and WHY THOR WHYYY do they look like that?



Well, here goes. I’ll identify for you those caterpillars that I recognize from this video, and give you a short explanation as to why evolution allowed them to become the fuzzy little weirdos you see in this video today. Sorry Creationists, the answer is not “God predicted the existence of viral videos and wanted to have a laugh”.


Evolution can often push organisms towards funny shapes and colors and usually (in the case of critters especially) this is has something to do with their defense mechanisms, and how they avoid getting eaten.

Let’s start with the first caterpillar, with the large spikes and the green patch on its back.

This is a saddleback caterpillar, or Acharia stimulea. This caterpillar uses bright colors to indicate that it is poisonous, a technique known as aposematism, and those spines protruding out of the front and back bits are indeed full of venom. When it comes to brightly colored creatures, unless they are birds or tropical fish, it is a good bet that they are poisonous, so keeping your distance is advised. Of course they might just be pretending to be poisonous, which is also a common defense mechanism, but that is a topic best left for another TWIZ.

The saddleback caterpillar is found across the East coast of the US, and it grows into a slug moth which is far less odd-looking than it is as a youngster.



As an adult, it abandons its aposematic coloring and instead opts for the less energetically costly option of looking like a dead leaf, hoping to fool its predators into leaving it alone by blending into its surroundings rather than brightly warning them to stay clear.

The second one in the video, with the red and black stripes that reminds me of the red-faced bad guy in Star Wars I I don’t recognize, although based on the coloring I think it’s a good bet that we have another example of aposematic coloring.

The third I recognized immediately, as it is one of my favorites.

It is called a monkey slug, or Phobetron pithecium. It’s resemblance to a nasty hairy tarantula is not an accident, but rather it is the point of its odd body shape. Those fuzzy protrusions coming out of its back have no other function than to expertly disguise this caterpillar as a big hairy spider. It grows into a hag moth, though as usual, the adult form is nowhere near as cool and weird looking as it’s younger self.

Caterpillars really do embody the concept of experimenting with weird and extravagant forms of dress and makeup as teenagers, then settling into their boring suit-and-tie adult selves.

The fuzzy, orange/brown caterpillars at 0:14 look like puss caterpillars, which are found in Florida, and are amongst the most poisonous caterpillars in the world. They grown into hawk moths and, in a twist on the common habit of caterpillars, their adult form is just as funny looking as its younger one.



While they are incredibly poisonous, you will notice that they do not show off their venom with bright colors like the saddleback caterpillars do. Instead they opt for the extremely fuzzy look, which is not a very appetizing body plan for birds either. Unfortunately humans, especially children, find fuzzy-looking things appealing to pet if not to eat, which can result in extremely painful stingers getting lodged in your skin. So, if you see one, try your best not to touch it.

This video is just a taste of the weird caterpillars that are out there. There are other lists of the wide, varied and utterly bizarre caterpillar world, and of course some of my personal favorites, the spicebush swallowtail caterpillar, which plays a pretty convincing snake, and the giant swallowtail caterpillar, which is excellent at looking like a piece of bird poop.

So, there you have it, the bizarre appearance of most caterpillars all simply come down to the many solutions they have come up with to not being eaten. Whether it is developing poison, and displaying the fact that you’re poisonous to everyone around you, imitating a tarantula, a snake or a piece of poop, or simply looking so incredibly odd that no one will dare try to eat you, the end result is the same: survive long enough to make it to adulthood and reproduce.

The evolutionary explanations are always so much more fun.

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