The Farmer Diaries

Texas farmer defends maligned, misunderstood hornworm

Texas farmer defends maligned, misunderstood hornworm

photo of tomato hornworm
A tobacco hornworm feeds on a tomato plant in Marshall Hinsley's hydroponics test garden. Photo by Marshall Hinsley
photo of hawk moth feeding from tobacco
A hawk moth uses its long proboscis to drink nectar from a tobacco plant growing near Hinsley's garden plot. Photo by Marshall Hinsley
photo of pesticide containers
Hornworms illustrated on bottles of pesticides show just how much contempt there is for the caterpillar. Photo by Marshall Hinsley
photo of tomato hornworm
photo of hawk moth feeding from tobacco
photo of pesticide containers

If it's your first time to grow tomatoes, you'll eventually walk out among your plants and find one or two of them stripped of their leaves. What may have been a robust tomato plant full of promise the day before will suddenly have become a skeleton of branches with a few green fruits remaining, and some of those may be partially eaten too.

Demoralized, you can't help but seek an answer for this instant misfortune. You'll look among the bare branches, trying to grasp what has happened until your eyes are drawn to the last cluster of leaves still left on the plant. You reach out to touch the branch, which has an usually thick portion of stalk and — good golly, Miss Molly — the branch arches back and reaches out toward your hand, revealing itself to be the largest and most animated worm you've ever seen, almost as long and definitely as big around as a cigar.

 So voracious is a hornworm's appetite that it can denude a plant in a day, evoking the ire of gardeners who can't be blamed for wanting vengeance.

The sight of a tobacco hornworm is shocking, even to experienced farmers. Each year when I find my first one for the season, I admit I am a little startled. Blending in so well with their host plant — usually a tomato but sometimes peppers, eggplants and potatoes — they escape detection until I'm face to face with them. Light green, with small spots that look like rows of eyes running down both sides of their plump bodies, they have an intimidating stinger at one end that accounts for why they're called hornworms. 

In fact, the horn has no sting to it at all; it appears to serve no purpose except to aid in its camouflage, looking like a bit of stem. Still, the caterpillar has a menacing look that keeps predators back and gives gardeners pause about pulling them off their plants.

So voracious is their appetite that they can denude a plant in a day, evoking the ire of gardeners who can't be blamed for wanting vengeance. Look at the garden sprays and pesticides at garden centers, and you'll see this tomato enemy clearly illustrated on their labels — a bottle of revenge for under $10. 

In online gardening forums, you'll likely see questions from newbie growers asking how to get rid of the pest, along with outcries for the destruction they've caused. Seasoned growers offer plenty of solutions, giving answers that often fall into the territory of creative and indulgent cruelty, with methods of killing the worms that reveal their pleasure in executing their enemies.

"I use two bricks, lay the hornworm down on one and smash it with the other," says a woman with a profile pic that looks innocent enough. "I stab them with scissors," offers an otherwise kind and gentle man. Someone else just throws them onto the hot asphalt of the road nearby and enjoys their slow death under the desiccating sun.

The refrain among growers is clear: all hornworms must die.

 This detrimental garden guest turns into a beautiful hawk moth, an important pollinator of nighttime blooming flowers.

What's not addressed in this chorus of death is that this detrimental garden guest turns into a beautiful hawk moth — so resembling a hummingbird when it drinks nectar from flowers that many people mistake it for one. Hawk moths hover over flowers and flit from one to the next, just like a hummingbird. Also known as sphinx moths, hawk moths use their extraordinarily long proboscises to drink nectar, usually at night, and are therefore important pollinators of nighttime blooming flowers.

The few days a hornworm spends building up its bulk by eating garden plants is more than paid for when it turns into a hawk moth and pollinates gourds, ornamental flowers and wildflowers. As part of the ecosystem where we plant our gardens, it has a purpose. Therefore, the calls for eradication with no mercy are shortsighted and self defeating, especially when we consider the plight of pollinators worldwide, dying off from the exponentially increasing use of pesticides in industrial agriculture.

I can't kill hornworms. I've seen their purpose, and I've witnessed their intelligence. On a warm afternoon when I was inspecting my hydroponically grown tomatoes, I came across a hornworm defending himself against a horsefly.

The fly was trying to bite the hornworm on his back, but the hornworm gripped the branch where he was with two of his false feet and swung the rest of his body at the fly each time the fly approached, like a little green baseball bat. The fly was persistent, but so was the hornworm. I was both astonished and somewhat disturbed by the hornworm's apparent degree of self-awareness. He grew fatigued by the battle, and I could tell he was distressed.

Killing conscious beings does not sit well with me. So to protect my tomatoes from loss, I choose other options that ensure the hornworms may fulfill their destiny. 

Sometimes I let them have the plant they're eating. If I plant a dozen or more tomato plants, I rarely find hornworms on more than one or two. I can spare a couple of plants.

 To protect my tomatoes from loss, I choose other options — like planting sacred datura — that ensure the hornworms fulfill their destiny.

In fact, I may plant a few extra and designate them as sacrificial plants. When I find a hornworm, I gently pry them off my other tomato plants and place them on my sacrificial plants. If I should ever plant tomatoes for commercial production, I would dedicate a couple of rows for hornworms. It's a sort of payment to Mother Nature for the plot of ground I've taken over for my own purposes.

Third, I plant sacred datura near my garden. Hornworms prefer sacred datura to tomatoes, so planting it near my garden draws the hornworms away from my crops.

Datura is a native ornamental bush that blooms at night; its huge white flowers emit a fragrance that can fill the air for a hundred yards away. As sacred datura is a night-blooming plant, hawk moths feed from the flowers, thus the datura provides for the complete lifecycle of the insect.

I've even begun to consider the potential of rearing hornworms in a brood chamber. By picking them off of my tomatoes and placing them in a container, I can feed the worms with sucker branches that I prune away from my tomato plants.

The suckers need to come off the plants anyway; feeding them to hornworms seems a perfect use for the spare branches. The worms will feed on the branches for a few days and then start to wander around in the container, at which point they're ready to build their cocoon and transform into a hawk moth. Details on how to raise hornworms into adults are available from the Manduca Project website.

I know that treating hornworms as guests in my garden who need to be accommodated, rather than pests that need to be eradicated, challenges the mentality of those who simply want to "get rid" of whatever's eating their plants. But aside from my appreciation of the unique and beautiful creatures they are at any stage of their lifecycle, I know that hornworms and the hawk moths they become serve a purpose in the natural habitat we occupy.

I prefer to find a way to work with this habitat. If we simply rid ourselves of everything that bothers us, I'm afraid that we could eventually wind up with a world that's as flat and bereft of beauty as a Walmart parking lot.