Had a tomato monster invaded our patch?
I looked closer and discovered more tell-tale signs, smalldark-green/brownish pellets called frass resting on leaves (Photo 2). Yes, definitely, there’s a hornworm—colored almost perfectly to match the tomato stems and leaves—somewhere on those plants. I consider hornworms to be oddly beautiful pests, but other gardeners think them repulsive monsters to be eliminated at any cost.
I began searching the two plants leaf by leaf, stem by stem. I was about to abandon the search when … there it was … almost perfectly camouflaged on a stem, larger than I had expected, about as thick as my index finger and early 3 inches long (Photo 3).
I tried to pick the hornworm off the stem, but it held tight with its many feet. I grabbed it in the middle but couldn’t get it off. As I was letting go, the hornworm suddenly raised and waived its head defensively at my fingers, something I hadn’t expected. The hornworm is designed for eating leaves, not fingers, of course, so I should not have feared, but to have such an unusual creature strike out at you is unnerving, to say the least.
I decided to move to Plan B and remove the stem that the hornworm was grasping and put it on a brick for picture-taking (Photo 4). Then I put the hornworm into the cup of soapy water. Good-bye, hornworm.
Two varieties of hornworms are common in area gardens—tobacco hornworms and tomato hornworms. Both are light green in color. Generally the tobacco hornworm has a curved red horn on its posterior and seven diagonal white lines on its sides. The tomato hornworm has a straighter blue-black horn and eight V-shaped marks. My monster, with its red horn, was a tobacco hornworm.
Hornworms feed primarily on foliage of plants in the Solanaceae family, such as tomatoes, peppers, eggplants, and tobacco. Tomato hornworms are the larvae of the Five-spotted Hawk moths, the tobacco hornworms the larvae of Sphinx moths.
During the cool hours of the day, hornworms move out to munch on exterior leaves, and during the heat of the day, they retreat to the plant interior to eat leaves and, occasionally, green tomatoes.
I handpicked and drowned my hornworm. Others cut them in half with scissors or stamp them on the ground. One of my acquaintances uses them for fish bait.
Beyond handpicking, biological controls work. Small braconid wasps are natural enemies of hornworms and lay their eggs on the hornworm’s back. The wasp larvae then feed on the inside of the hornworms and eventually form white cocoons that protrude from the hornworms. If you see the cocoons, let nature take its course. I do. The wasps soon kill the hornworm (Photo 5) and seek other hornworms to parasitize. Sprays with Bacillus thuringensis (BT) also are effective on young hornworms.
Some gardeners want to “nuke” every pest. Chemical insecticides can be used to control the hornworms, but to my way of thinking, handpicking and the parasite wasps are sufficient. I don’t mind sharing a few tomato leaves and maybe a green tomato. I definitely don’t miss the chemicals.
If I had young grandchildren or neighbor kids visiting, I’d show them my garden drama of tiny braconid wasp versus huge hornworm—and urge them “not to fear.”