INSTINCT IN THE ABSENCE OF THOUGHT
or THE CURIOUS CASE OF THE DROWNING CATERPILLAR
by Joey Poole
Recently, in the midst of a brutal July heat wave, I noticed that my azalea bushes were being absolutely skeletonized, eaten right down to the stems. A closer inspection revealed that the bushes were crawling with a horde of large (over two inches long) black caterpillars with striking yellow spots and bright red heads, tails, and feet. I’d been sent the pestilence of the Lord in the form of the red-headed azalea caterpillar, a notorious pest throughout the Southeast and parts of the Midwest.
Figure 1. Azalea caterpillars assume this pose when they’re harassed by predators or nosy gardeners. It’s not exactly the most threatening defense mechanism around.
I was a bit torn about what to do. I value insects—except for fire ants, which are invasive anyway—in my yard, and try to encourage native plants that some might consider weeds in hopes of attracting them. Figuring that caterpillars were at least as desirable as azaleas, a notion my pesticide-happy neighbors with prettier shrubbery understandably don’t share, I decided to leave them be. But when I checked in on the scourge the next day, the considerable amount of damage they’d done overnight made it clear that they would decimate the azaleas if left unchecked. Something had to be done.
Luckily for a few of the caterpillars, there was someone standing between me and total annihilation. Although she was revolted by the fact that I picked them off the bushes with my bare hands, my girlfriend’s nine-year-old daughter didn’t like the idea of killing the caterpillars, reminding me that they were baby butterflies (actually, the adult form of these particular caterpillars is a rather undistinguished, drab-looking moth, but that didn’t seem important). We decided that we’d keep a handful of them indoors and destroy the rest. Playing god by deciding which of the babies lived and which died, I plucked three of the caterpillars, one of whom was chosen because it looked like it might bear a parasitic wasp egg, off of the bushes before committing genocide against their brethren. We set our new pets up in an empty terrarium with azalea sprigs to munch on, waiting for them to spin cocoons and turn into moths, which we planned to release far, far away from our own beleaguered azaleas. Little did we know that our moth nursery would soon provide a fascinating glimpse into the power of instinct in the absence of the capacity for true thought in the form of a seemingly suicidal caterpillar.
In order to keep the azalea sprigs fresh for our new house guests, we put them in a glass of water, thinking the caterpillars would hang out on the leaves, safely high above danger of drowning. For a couple of days, they did. Then one of them started doing something that seemed to defy all logic, as if captive life had driven it insane. It started marching right down the branch, sometimes pausing at the water line as if trying to decide what to do, but more often simply charging on into the water. Underwater, it continued right on down the branch all the way to the bottom of the glass and then fell off, writhing hopelessly in the water because caterpillars, it turns out, can’t swim. Over and over the same caterpillar did this, and we saved it from drowning several times. No matter how many times we fished it out of the water and sat it back on the leaves, eventually it would get the same foolish notion and trudge headlong into danger.
Perplexed, we tried to figure out what was driving this caterpillar to attempt suicide. Depression was the obvious answer, but it’s an anthropomorphic mistake to assign human emotions to animals, especially insects. A little research on the life cycle of the azalea caterpillars revealed that, unlike many caterpillars, which make cocoons right on the leaves or branches of their plant hosts, Dantana Major burrows into the soil to pupate. This solved the mystery of the drowning caterpillar. Obviously, it was ready to get on with the metamorphosis—enough with the endless crawling and munching, munching and crawling! It was time to rest and then, if only briefly, to fly. The instinct woven into its DNA through a mechanism still largely unknown to science was driving it ever downward, even when that direction meant certain death.
This shouldn’t be surprising. Insects—and, arguably, all of us in the animal kingdom—are essentially biological robots, programmed to react in certain ways to certain stimuli. Like a moth driven to burn off its wings, Icarus-like, in a candle’s flame, this little booger was determined to find the ground, no matter what stood in the way. French entomologist Jean Henri Fabre famously demonstrated that processionary caterpillars, those who march in lines, nose-to-tail, will walk endlessly in a circle when their leader is removed and the line circles back onto itself. The caterpillars will continue to trudge around in a circle until they die of starvation or exhaustion, even when food items are placed nearby. The instinct to follow the line overpowers the drive to eat, and ultimately, the will to survive. Even mammals exhibit similar behavior, like the proverbial horse running into a burning barn or lemmings driven to mass suicide by population density and herd instincts.
Luckily, as primates, we’re a little better equipped when it comes to problem-solving. Some of the more regrettable aspects of the human condition notwithstanding, it generally pays to have a frontal lobe capable of critical thought, something that can override instinct when things get dicey. You wouldn’t, for instance, march calmly underwater, not even realizing that you were drowning as the water filled your lungs (or spiracles, as with the caterpillar) just to get to where you knew deep down in the very fiber of your being, way down in your DNA, that you were supposed to go, if your house were flooded. You’d stop at the edge of the water, scratching the skull covering your huge brain, and think about where you could spend the night.
The caterpillar that seemed bent on drowning itself didn’t have the luxury of thought, which never would have mattered in its natural habitat, where there would be no standing water at the bottom of the world. Pausing to question its instincts or other such dawdling on the way to make a cocoon in the ground would be a good way to get eaten by a bird or a lizard, rendering its brief life a genetic failure.
It’s easy to look down our noses at such mental simplicity. But let’s not get too high and mighty here, because our huge frontal lobes don’t always protect us from ourselves. If they did, we wouldn’t smoke tobacco knowing that it might give us cancer or call our exes in the middle of the night, knowing that it can only result in heartache.
Figure 2. Only a tiny fraction of the horde eating our azaleas.
As for the caterpillars, who might not be able to ponder their own fates but will also live out their lives without ever tasting heartache? Well, we couldn’t exactly kill them after we’d gotten to know them, so we decided to set them free to eat the azaleas in a local park. My apologies to the municipal landscapers.
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Joey R. Poole is a writer and strictly amateur naturalist from Florence, South Carolina. His fiction and non-fiction have appeared in places like The Southeast Review, Adirondack Review, Clapboard House, and Bartleby Snopes. Like everyone else, he’s hard at work on a novel.