But the tiger beetles have evolved that ability to survive, since their larvae burrow into sand which is liable to flood for days. What about solely terrestrial insects? Like, say, butterflies and their larvae? Turns out even they can survive a bit of dousing, or at least one of my caterpillars this summer did.
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| First instar Black Swallowtails are barely larger than the type on a park brochure! |
One day I came home and checked on a day-old Black Swallowtail caterpillar like the one shown above, only to find that it had slipped under the surface of the water reservoir instead of staying on its dill sprig. (Note to self: watch out with tiny caterpillars and tiny dill sprigs!) My heart nearly stopped. I had even watched this egg being laid by the butterfly right beside me as I weeded the garden, so I was especially attached to this particular caterpillar. I had no idea how long the caterpillar had been underwater-- it could have happened hours ago. But just in case, I fished out the little body. How on earth do you give CPR to a millimeters-long caterpillar? For that matter, I don't know if you even could do CPR for caterpillars. Like other insects, they breathe through multiple openings, called spiracles, along their sides. Mouth-to-mouth wouldn't exactly work.
Out of desperation, I just blew gently on the soggy, limp little black caterpillar. And it started to move! As the line from Monty Python and the Holy Grail goes, "I'm not dead yet!" I transferred the caterpillar carefully to a fresh sprig of dill, and kept it under close observation for a few days.
Once it was clear my caterpillar was out of danger, I became curious. Could caterpillars hold their breath at will? How, and for how long? This question sent me down a rabbit hole of research. I haven't yet found information specific to caterpillars, but did find one intriguing paper from 2005: "Insects breathe discontinuously to avoid oxygen toxicity," by Stefan K. Hetz and Timothy J. Bradley (Nature 433, 516-519). The researchers suggested that unlike us continual-breathers, insects keep their spiracles closed most of the time, opening them briefly and infrequently to release carbon dioxide and inhale just enough oxygen. The original paper is behind a paywall, but it's summarized in this article at LiveScience. So my caterpillar didn't hold its breath, exactly, so much as just keep its spiracles closed and use the oxygen already in its system, while it was underwater. Pretty cool!
Over the next few weeks, the caterpillar munched down all the dill I could provide, and grew quite normally. Despite the underwater episode, it actually turned out to be one of my largest caterpillars ever. Now, I don't actually measure my caterpillars, either their length or their overall weight-- I take a fairly hands-off approach most of the time. But just eyeballing, it seemed larger than the other caterpillars I had raised a few days before.
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| So fat and happy! And no longer soggy in the least. |
It pupated not long after I took this photo, and then successfully eclosed yesterday: a healthy female. Even my husband remarked that the butterfly seemed larger than usual, corresponding with its large larval size. After a few minutes of warming up in the sunshine, off it fluttered. Hooray!
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| The freshly eclosed Black Swallowtail, ready to fly off into my yard. |
So moral of this story is: don't give up, even if your caterpillar falls into the water. They're amazingly resilient. No wonder they and other insects are predicted to take over the world someday!
