Pink Caterpillar

2009 September 19

So, I’m on my way home, pushing my bike up the last steep hill, when I look down and see this very, very pink caterpillar just starting to cross the road. Now, a shocking pink caterpillar is not something you see every day, so naturally I picked it up to bring it home.
Angulose.prominent.side

I didn’t have a container or anything, so I had to carry it in my hand. It didn’t like this, and kept thrashing around pretty vigorously. It was about an inch and a half long, so it was pretty substantial and quite strong. The weird thing was, after a bit it stopped thashing and started slowly rubbing against my hand, and I could feel a vibration. And then, when I held my hand up to my ear, I could hear a faint purring[1]. This was very disturbing, it was an odd and not particularly pleasant sensation. If I’d been a predator, I probably would have dropped it. I was a little bit afraid that it might be putting some irritating or corrosive chemical on my hand, but no, it wasn’t. But somehow, the vibration was making it feel as if it was.

Angulose.prominent.head

So, anyway, I got it home, showed it to Sam, got some pictures, and then sat down with “Caterpillars of Eastern North America” and started browsing.

Angulose.prominent.dorsal

I didn’t have much luck at first, there are only a few species of pink caterpillars and most of those are kind of hairy or warty, and this one was smooth. At first I thought it was an Angulose Prominent, Peridea angulosa, based on an inset picture of one of its color phases in Caterpillars of Eastern North America – they are normally green, but in the fall they sometimes turn pink.

But, as it turns out, it probably is not a prominent at all. Down in the comments, John and Jane Balaban (who are contributing editors to BugGuide) noted that it is more likely one of the Cucullia owlet moths, which are both very colorful and highly variable in both color and pattern. For example, a few of the pictures of Cucullia asteroides are a very similar shade of pink with yellow side stripes (along with a lot of others that look completely different!)

Angulose.prominent.ventral

This immediately raises a question, though: why on earth would any caterpillars sometimes be pink? Well, in the fall, it’s probably because the tree leaves that they are eating turn some shade of red or pink in the fall[3], and so changing color with the leaves is much better camouflage than staying green. I expect that what happens is that, when the trees start producing their reddish leaf pigments as the weather cools, the caterpillars eating the leaves take up the pigment in their skin, and so they change color too.

—–
[1] The whole way home with a purring caterpillar in my hand, I kept being reminded of something that Don Marquis[2] wrote about fishing for bullheads (a type of particularly rugged medium-sized catfish): “And then, once out of the water, they will advance on you with an odd purring noise and try to horn you with their spines, showing every indication of wanting to fight it out on land.”

[2] Don Marquis was mainly known for a series of poems he published in the 1920s and 1930s, written entirely in lower case, that he claimed were typed by a cockroach named Archy. Archy typed by jumping on the typewriter keys, and it was all in lower case because he couldn’t work the shift key.

[3] It turns out that the color change of the leaves in the fall is no accident, it’s not just a case of dying leaves exposing a base color as the chlorophyll breaks down. The color comes from pigments that the trees produce to protect them from the sunlight. I read an article about why leaves turn color (I think it was in American Scientist), and they pointed out that leaves aren’t just casually soaking up sunlight that is otherwise harmless. Rather, they are juggling nuclear fire from the heavens[4], trying desperately to capture the energy without getting burned. They can use pretty much all the light they catch in the warmth of the summer, but as it gets colder their ability to convert light to food drops off faster than the intensity of the light. Unless they do something, they’ll get singed. So, the leaves produce pigments (usually red or yellow) to filter out the most damaging wavelengths while allowing the leaves to keep photosynthesizing for just a few more weeks in the fall.

[4] The sun is a mass of incandescent gas[5], a gigantic nuclear furnace. Where hydrogen is built into helium, at a temperature of millions of degrees. Or, to put it another way, “There have been many arguments about how far a nuclear reactor should be from inhabited areas. Extensive historical experience has shown that 93 million miles is probably far enough.”

[5] OK, ok, actually the sun is a miasma of incandescent plasma, but that requires completely rewriting the song.

9 Responses leave one →
  1. September 21, 2009

    Now I’ve heard everything! A caterpillar that purrs. Next, it will be begging for kitty treats.

  2. November 8, 2010

    I think this may be my caterpillar! The only difference is that it’s underbelly was not green, it was also pink, and it didn’t have those black stripes that I could tell. Instead it had one lighter pink stripe down the middle of it’s back, like in your picture, and the rest was a solid and darker shade of pink. It also had two tail thingys on its rear end, and a dead fire ant attatched to it’s butt.

  3. November 9, 2010

    Amber: You probably found a close relative, there are a number of the “Prominents” that have a pair of extended tails like you describe. Since you mention a fire ant, I expect that you are much further south than me.

  4. Jane and John Balaban permalink
    December 5, 2010

    This caterpillar is more likely a prepupal Cucullia. Caterpillars often change colors as they prepare to pupate. This may be the Asteroid, Cucullia asteroides, Wagner pg 388.

  5. December 6, 2010

    Thanks for the correction. I see the BugGuide description for Cucullia says of the caterpillars “the range of variation between species is too complex to describe in general terms”, and looking at the pictures I can believe it. They’re quite pretty, but holy cow are they variable.

  6. Velma permalink
    September 1, 2011

    I live in Moreno Valley California and this little one is the one that keeps coming into to my bedroom. There have been at least 7 so far. Pink/Mauve top then the color goes softly into a pale green underbelly. They are just beautiful. Isn’t it odd that it is here in southern california?

  7. joann permalink
    September 18, 2012

    “93 million miles is probably far enough” Awesome quote!

  8. kay permalink
    July 11, 2014

    I have now had two to five of these pink caterpillars every day in my pool this month, and this week one of them on my kitchen floor. We have lived in Galt, CA for 17 years and this is the first time I’ve ever seen this type of caterpillar. I am a life long resident of northern California and have never seen it in any other regions where I have lived before. Has anyone identified it yet?

  9. Lisa permalink
    July 15, 2014

    @Kay,
    I’m just south of you here in Lathrop. Found one about two weeks ago trying to embed itself into my entry way carpet. I thought nothing of it until I came home last night and saw four crawling up the house, near the front door . And if that’s not enough today my toy poodle found one in my kitchen Ewww. I’m not a fan of insects of any kind and keep a very clean home so I’m disturbed by the catapillars /worms or what ever they are and not happy they’ve decided to visit. I’ve been in this hose since 2001 and have never seen these before. I’m also hoping someone else has some info on these things.
    Do you have palm trees? Saw this post about PALM CATAPILLARS
    I have several,had them for yrs, and never had pink wormy things . Here’s the link. Hope it works.
    http://cals.arizona.edu/maricopa/garden/html/t-tips/bugs/plm-ctpl.htm

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