Pity the poor hornworm

I remember the absolute horror I felt when first confronted with hornworms – huge creatures perched on my tomato plants and chewing so fast you could watch the leaves disappearing. They get their name from the horn-like protuberance at the rear end.

Authorities (in those days gardening books rather than the internet) were uncompromising. Get rid of them or your tomato patch will be devastated. You will have no tomatoes left.

Apart from pesticide, which I avoid, various methods were proposed, all of which involved actually picking the creatures up – and then either dropping them into some deadly solution or stomping on them. The first option meant watching them writhe in agony, the second meant yucky goo exploding underfoot.

Neither was acceptable, so I would clip the host leaf off and carefully carry it to a ditch far away from any tomatoes, there to die of predation or starvation, out of my sight and not directly by my hand.

In recent years I have taken an ever keener interest in what’s living in my garden. Life in all its forms is fascinating. So when the Big Green Munchers made their presence known last week by way of leaves gnawed back to the stem, I decided to get to know them. First step was to find out their proper name, rather than their ugly colloquial moniker. They are the caterpillar of the Five Spotted Hawk Moth (Manduca quinquemaculata), a large brown and grey moth that, I found out, is part of the Sphinx family, as is the very interesting Clearwing Hummingbird Moth I spotted earlier this summer; it has a quite extraordinary resemblance to a hummingbird. 

Already they seem less like aliens from outer space.

The next day, I found two of them, two inches long, chewing away, and was pleased to note that they weren’t eating my prized Stupice tomatoes which are staked and pruned rigorously – all suckers taken out as they grow and the topmost growing tip pinched off a few weeks ago to direct al the plant’s energy to the fruit.

Instead they have emerged in a tangle of cherry tomatoes that I’m not too keen on because they’re not as sweet as promised.  I didn’t bother to prune the cherries, thinking they would be tidy determinate bushes. Instead, they sprawled and now the hornworm were doing the pruning for me. Or so it seemed.  

Still, I felt a little concerned the next day to count five, eating hard. The cherry tomato patch looked pretty luxuriant but I began to hope for the natural allies that are supposed to flourish in my unsprayed organic veggie garden. I read that birds will eat these caterpillars, and I have lots of birds visiting a nearby feeder. And there’s a parasitic wasp that has larvae that consume their insides (the suffering of various species of caterpillars preyed upon by this family of wasps caused a theological crisis for Charles Darwin, I learn from an excellent book I'm reading - The Forest Unseen by David George Haskell.  "I cannot persuade myself that a beneficent and omnipotent God would have designedly created the Ichneumonidae with the express intention of their feeding within the living bodies of caterpillars," Darwin wrote).

By this time – day four - the caterpillars had become objects of scientific inquiry rather than home-grown terrorists. I’d pop out to visit them regularly, cautiously eying their rate of growth – up to three inches now – and watching the curious way they move along the leaf, two pairs of pudgy feet at a time.  

On the fifth day, I could only find two and then I had to leave for two days. When I returned, the tomato patch looked just fine and we seemed to be down to one very large caterpillar. Perhaps the birds took care of business. 

Two days later, still only one. The invasion of the killer worms seems to be over. The next step, if it survives, will be for the caterpillar to pupate, which it does by dropping to the ground and spinning a cocoon. Immobile inside a hard protective coating, the pupa will spend the winter in leaf litter and emerge as a moth in spring to fly off searching for tomato plants to lay its eggs on. Which is one reason why cleaning up leaf litter in the vegetable garden is a good idea. 

It’s also why it’s a good idea to leave leaf litter in place, for instance around Arrowwood, Hawthorn, Snowberry or Honeysuckle, some of the host plants of the Clearwing Hummingbird Moth. I really want to see it again.  

The Five Spotted Hawk Moth seems to be a survivor, no matter how meticulous you are about cleaning up the tomato patch. So I expect it back, regardless. That’s okay. I’ll leave it a few volunteer tomato seedlings. Just stay away from my Stupices.  


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