Bubbles? Did I just see a lily pad blowing bubbles? I had waded out into the pond to take a picture of a photogenic water lily. Out of the corner of my eye, I got the impression I had just seen bubbles popping on a water lily leaf. I turned and looked at the suspect lily pad. There in the very center was a small oblong piece of leaf on top of the lily pad. Assuming this was a leaf shelter, I became rather interested in it, forgot about the lily bloom, and momentarily forgot about the bubbles.
Is this my mystery water lily stem-borer caterpillar I’ve been trying to figure out for years? I wondered. Quickly I pulled off that leaf shelter, and, sure enough, there was a small hole in the lily pad with a bit of caterpillar visible. That’s strange, I thought. My original caterpillar had a leaf shelter under the lily pad covering a hole in the stem. I turned the lily pad over. No leaf shelter and no visible hole in the stem.
Disappointedly, I laid the lily pad back down on the water. That’s when my new leaf-sheltered, stem-borer caterpillar blew off a couple more bubbles and “blew my mind.” That’s because, right then, I realized that this caterpillar was stealing air from the water lily’s air circulation system while hiding in the strange, wacky-looking space inside a water lily stem. My caterpillar was turning legendary!
You see, before I saw it blow bubbles, I was picturing this caterpillar feeding like a stem-borer on the inside of the water lily stem and imagining how it would, while it was eating, deal with the many star-shaped, thorn-like things (called astrosclereids) in the leaf and stem. These help give the water lily leaf and stem their tough, flexible structure. But, after I saw the caterpillar, or rather, the lily pad blowing bubbles, I realized the caterpillar might be in the stem for the sake of the air flow that was coming from the water lily’s convective air flow system.
This air circulation system works like this. Air is taken in through the stomata of young leaves (which are on the top side of the lily pad) and travels through the lily pad’s air spaces, down the stem’s air canals, through the roots, up another stem, and out the leaky older lily pads. This circulation system aerates the roots and apparently my caterpillar.
So, back to the story of when I saw the lily pad blow bubbles—right then and there I plucked the lily pad, stem and all, waded back to shore, and placed it in a gallon Ziploc® bag that I carry in my camera bag for such a time as this. Back home, the water lily leaf was soon floating in an aquarium for observation of the caterpillar. I was hoping to learn more about the caterpillar’s life story and figure out what kind of moth it would turn into.
What I was not expecting to discover was that I was dealing with an extremely shy caterpillar. I noticed that it stretched timidly out from its leaf shelter/stem retreat to feed on the palisade layer of the lily pad. If I approached too quickly, accidentally bumped anything, or if the camera flashed, the caterpillar was gone in a flash. This caterpillar was obsessed with hiding. Obviously, the Creator didn’t give it chemical defenses or other physical means of protecting itself. He simply gave it the instinct to hide.
Another surprise the caterpillar served me was how it feeds. It wasn’t feeding by boring into the stem like I assumed it would. Rather, it reached out from its covered hole/stem home to feed, producing a fan-shaped scar on the pad. Its style of feeding on just the top leaf layer is called “window feeding.” So, is this caterpillar not a stem-borer after all? Could the hidey-hole in the stem be just an underwater hiding place complete with an oxygenating air flow system?
I had to go back to the pond and look for more evidence of window feeding radiating from around the central area of more lily pads. Sure enough, it was fairly common to see the radiating feeding pattern. Some feeding signs had no leaf shelters, and these appeared abandoned. Often nearby was another lily pad with a leaf shelter blowing bubbles.
Now I wondered, could I do an experiment to see if the air flow was coming from the caterpillar, the stem, or the leaf? The day I went back to the pond was sunny, and I saw many lily pad leaf shelters blowing bubbles. It was a perfect day to do an experiment! I found a very bubbly lily pad leaf shelter.
- I snipped off the stem a couple of inches under the water. The bubbles kept bubbling.
- Next I chopped through the stem and caterpillar. The bubbles kept on coming.
- I cut across the leaf and through the main leaf vein. That really slowed things down.
- I cut off the one side of the lily pad. That slowed things down even more.
- I cut the rest of the leaf off. The bubbles stopped.
I repeated this a few times and had the same results, which tells me the air flow was coming from the leaf. The last time I noticed a stream of small bubbles coming from the main vein of the leaf. That tells me the lily pad is pressurizing the air in the air canals. Fascinating! I wonder how it does that.
Well, I still don’t have an answer to another question: When and where do these lily pad caterpillars pupate? Will I get an October surprise and witness the caterpillars turning into moths right there on the lily pads? Perhaps the caterpillars pupate in the stems, since I found a hole in a stem that was blowing bubbles. It is possible I’m seeing more than one species, and they have different life stories. Perhaps I’ll have to wait until spring for the moths to emerge. It is even possible that the caterpillars swim to shore to pupate, and when I’m scratching around to find them, I’ll learn how to find truffles.
Anyway, the epic quest to figure out my water lily caterpillar’s life story has given me many opportunities for discovery. I’m game!