By Karen Miller, Master Gardener Entomology Specialist
Do you know “what’s buggin’ me”? The loathing gardeners have for the tomato hornworm is what’s buggin’ me! Yes, they are ugly and they can destroy a tomato plant in record time, but they are a caterpillar, or larvae, and later morph into the beautiful sphinx, or hawk, moth. I have to admit I have squashed many in my gardening days, but I still remember the day I vowed never to kill another tomato hornworm. I was a Master Gardener trainee sitting in my entomology class when, to my horror, the instructor enlightened me and my class. I am not sure just what I thought the tomato hornworm was, or even where it came from, but I certainly did not know it was the sphinx moth in its larvae stage. The tomato hornworm c a t e r p i l l a r , M a n d u c a quinquemaculata, is in the family Sphingidae and is found throughout the United States, northwestern Mexico and southern Canada. Tomato hornworms are closely related to and sometimes confused with the tobacco hornworm. They are considered cousins in the insect world, and caterpillars of both species feed on the foliage of various plants in the Solanaceae family. Both species can be found on tobacco or tomato leaves, and the plant on which the caterpillar is found does not always indicate its species. Each species has distinct lateral markings: tomato hornworms have eight V-shaped markings while the tobacco hornworms have seven diagonal lines. Also, the tomato hornworm has a black horn on its back end, the tobacco hornworm has a red horn. Both caterpillars turn into large moths with a four to six inch wingspan in colors ranging from brown and gold to pink and grey. The tomato hornworm is a voracious feeder, but tomatoes are not the only plant they eat. They will feed on eggplant, pepper, moonflowers and potato.
You know you have a tomato hornworm when you go out to your garden and find your tomato plants have been defoliated. You will also find black droppings of poop on the ground below. Spotting these caterpillars is a difficult job because their green color is so like that of the leaf. By using an ultraviolet light at night, a sharp color contrast can be seen between the hornworm and the foliage, thus, helping locate the hornworm. In the final instar, the tomato hornworm will drop to the ground and pupate in the soil, though some will spin cocoons in leaf litter. In areas where winter occurs, this moth can overwinter in the pulpal stage, emerging as an adult in spring. Several species of the sphinx moth are ecologically important because they pollinate several types of flowers and plants. Also known as hummingbird moths, the sphinx moths are fast and strong flyers with rapid wingbeats. Sphinx moths have the ability to hover at flowers, much like hummingbirds. Some even resemble bees and hummers moving side to side and sometimes stopping in midair. Most are nocturnal, though, some do come out during the day. I mostly observe them feeding in the late afternoon. Bottom line…I would like to suggest to those of you with internet access to research these magnificent creatures. I had no idea the number and varieties that exist in our world. I believe gardeners can live in harmony with the tomato hornworm. One suggestion is to plant a sacrificial tomato plant away from your garden crop. Keep the blossoms removed and feed plant with lots and lots of nitrogen fertilizer to grow lots of leaves. Take the caterpillars you find on your garden crop and relocate them to the sacrificial one. You can even bring them to me, I have plenty of non-producing heirloom tomato plants I can put them on. This should provide you with a sphinx moth to enjoy, maybe even two or three.