Contemplation of a Hornworm

Katherine Purvin

© Copyright 2023 by Katherine Purvin

Photo courtesy of Wikimedia Commons.
Photo courtesy of Wikimedia Commons.

It is easy to overlook the smallest and most varied of creatures; insects, arachnids, and various other arthropods are a constant of daily life that we do not even think about their presence, save when it overlaps with our own. The wolf and recluse spiders that creep along our baseboards, the fruit flies and fungus gnats that spin about the kitchen and the potted plants; the crickets and cicadas that make up the symphony of summer nights. Yet an encounter with these creatures can be just as wondrous as with any greater beast.

Take, for example, the mantis in the garden that stalks among the cucumber leaves, the shy hummingbird moths that compete with bumblebees and skipperlings for their place at the milkweed blossoms. And, of course, the crown jewel of that habitat, the monarch butterfly whose larval bands of golden-yellow are exchanged for wings of rich orange, its black stripes becoming night-velvet veins, the white stripes transformed into starry speckling along the wings’ edge. All of these and more, everyday enigmas that can be found if only one knows where and how to look.

And it is this knowing that is key to so many of these encounters; quite often, and as they are designed to be, they are hidden in plain sight—a marvelous thing that must be seen to be believed for some of these creatures. In my case, it was the humble tobacco hornworm—although perhaps humble is not quite the right word. They are massive caterpillars, when they reach their full growth, and are notorious as an agricultural pest—much like their close cousin the tomato hornworm (and which they very closely resemble), they can wreak havoc in the garden. And yet they remain very hard to find despite their size and voracious appetite. Their colors blend them in perfectly to the stems and leaves of a tomato plant; from the proper angle, their front ends can be mistaken for the young fruit of the cherry and plum varieties. Even if you know what you are looking for, it takes painstaking examination to find one, first by searching out the signs of their presence (nibbled-on fruit, leaf-stripped stems, and, of course, large frass pellets caught in nooks and crannies), and then by searching every part of the plant. One must look up, look down, look left and right and on the diagonal; then, from the corner of your eye, the caterpillar appears in a place you swear there was nothing before.

Sometimes it takes a couple minutes, sometimes longer; when I first spotted the frass, larger even than that of a monarch on the cusp of pupation, it took a while to trace it back to its maker. After all, frass cannot reliably tell you how recently the caterpillar was there, only that it was, and despite its apparent size, the hornworm was far more suited to escaping notice than a fifth-instar monarch, whose flashy warning colors make it easier to spot—and even then, they can be quite easy to overlook. But there is a certain skill learned in the rearing of monarchs, in the evening hours spent searching for pearly eggs and tiny larvae by flashlight—you learn their preferences, where they are most likely to be found on their host plant, and how to quickly spot them. The same holds true for the hornworm. And so I found it, its fat body resolving out of a stem bent under its weight and the weight of the cherry tomatoes it was using as both food and camouflage.

A fifth-instar monarch, just before pupating, is about the size of a finger—two inches long or thereabouts, and a little over a quarter-inch wide. A fifth-instar hornworm is much larger, doubling these dimensions. There was no doubt as to the age of the caterpillar in the garden, far larger than any of my monarchs; here was the giant full-grown, soon to seek the earth and pupate. It hung quietly, its front und curled slightly; the late-instar monarchs would assume the same position when they slept. It was a fascinating creature—the face of a caterpillar is a strange, uncanny thing, and while a monarch’s stripes gave it more of a “face” than other species, it was in the hornworm’s features, magnified by its size and without any obscuring markings, that that alien biology could be more greatly appreciated. So too with the rest of its shape—the soft accordion-folds of its body around the meeting of false-leg and body, the suction-cup structure of these hind feet compared to the delicate claws of its front limbs; the unusual texture of its skin. Monarchs have a velvety, rubbery feel, not unlike that of a novelty eraser; I wanted to take the hornworm from its perch, to see if it was the same, or if it was rougher, as the faint lines on its back appeared to suggest. To see how much of my palm it filled when curled, if its suction-cup-tipped false-legs generated a stronger version of the gentle puck-puck-puck sensation that a monarch’s did as it wandered across my hand. And its silk—would it tickle as much as a monarch’s did, as it created a path to follow?

In the end, I left the hornworm where it was. The great green caterpillar would not appreciate being disturbed, and as much as there was a part of me that wished to bring it inside so that I might be able to witness its transformation from caterpillar to moth (and so that it might complete that transformation without the threat of predators), I knew that I lacked the knowledge needed to properly care for it. Late-season hornworms overwinter in the pupa—knowing that my monarchs would likely be a part of the southbound generation, it was best to assume that the hornworm was one that would emerge as a moth once winter had passed.

And it was impossible to say what might transfer if I touched it. Monarchs are at once surprisingly resilient and surprisingly fragile—losing part of a brood to sickness was not uncommon, and I did not want to risk transferring a pathogen from the hornworm to my caterpillars. Likewise, though I raised my monarchs from the egg and took great care in their tending, I wanted to avoid risking a potential transfer from a monarch to the hornworm—it was best for them all if I let the hornworm be.

Later, while researching the hornworm to identify its specific species, I came across a bit of trivia—that in fifth-instar caterpillars, just before they pupated, it was possible to watch their heart beat through their skin. I knew it was possible to see the heart of a caterpillar—the thin line that ran down the middle of their backs, which on a monarch appeared as a series of dark spots due to their markings obscuring much of it. But to see it beat—this I hadn’t heard before. So as dusk fell I went out to the garden again, seeking the hornworm to see if it was true. When I found it again I spent some time studying it, but though I could see the heart, it did not seem to beat—but, perhaps, I was simply a little too early. The caterpillar was in its final instar, but being unfamiliar with the breed, it was impossible to say how close it was to pupation.

I returned to the garden the next night—once again, I located the hornworm, and once again, I examined it by the bright glow of my phone’s flashlight. And this time I could see the blue line that was the hornworm’s heart gently pulsing. It is a strange thing, to so clearly watch the measuring of a life; to see such a vital piece of biology so vulnerable. And the hornworm is, of course, unaware and unconcerned of such things, including the fact that it is being contemplated—its place in the world, the trials it had and would face, how fickle the luck that had kept it alive and could yet doom it, and the influence an outside force could have upon its path.

There is a lesson to be learned in such an encounter, in the contemplation of a caterpillar. I spent several minutes more watching the hornworm, thinking, and then headed back inside to tend to my monarchs. It would be gone the next day; I would never know whether or not it had pupated or if its luck had finally run out. But I like to think that it survived, emerging as a hawkmoth the following spring.

Katherine Purvin currently resides in Springfield, Missouri. She is a student at Missouri State University, studying computer animation.

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