Gardening Harmful insects

Tomato Hornworms Are Easy to Control

20170804A Whitney Cranshaw, Colorado Ste University, WC
Although big and scary-looking, the tomato hornworm is harmless to people. Photo: Whitney Cranshaw, Colorado State University via Wikimedia Commons

You suddenly find a leaf on your tomato plant has been almost eaten off. And the next day another, then yet another? This is the usual symptom of the tomato hornworm (Manduca quinquemaculata), a menacing-looking (but harmless to people) huge green caterpillar 4 inches (10 cm) long. You can also find it on other plants in the nightshade family (eggplants, peppers, nicotianas, potatoes, daturas, etc.), but it does seem to prefer tomatoes. It has a similar-looking cousin, the tobacco hornworm (Manduca texta) with the same host range, but it prefers tobacco plants (Nicotiana).

Manduca quinquemaculatus a.k.a. Five-Spotted Hawkmoth a.k.a. tomato hornworm
The adult sphinx, almost the size of a small bird, is rarely seen. Photo: User:Lpm, Wikimedia Commons

The adult sphinx is a large, narrow-winged, dull-colored moth that beats its wings at high speed and pollinates many flowers … including, oddly enough, flowers of several nightshade relatives, like nicotiana and datura, the same plants its caterpillars eat! Because of its very nocturnal habit, the adult is rarely seen, although there are other smaller sphinx moths you may well see pollinating flowers during the daylight. The female lays its eggs underneath the leaves of the host plant and the larvae hatch in only 3 to 5 days. There are two or more generations per year.

This is an excellent example of a case where hand picking is the only “insecticide” necessary. That’s because there is usually only one hornworm per plant, rarely two. Why would you spray an entire plant with a possibly toxic pesticide just to kill just one bug? It’s so much easier to locate the caterpillar, remove it and “dispose” of it. (Usually, I knock it to the ground and squash it under my shoe, but the more squeamish could simply drop it into a cup of soapy water.)

But, despite its enormous size, this caterpillar is almost the same color as the foliage and can be hard to see. If you see chewed leaves but not the pest, spray your plants with a jet of cold water. The caterpillar will react by thrashing about … and is then easily spotted.

The tomato hornworm is found throughout the USA as well as in southern Canada and northern Mexico, but is most common in the northern part of its territory while the tobacco hornworm, which has a similar range, tends to be more common in the south.20170804A Whitney Cranshaw, Colorado Ste University, WC


Garden writer and blogger, author of 65 gardening books, lecturer and communicator, the Laidback Gardener, Larry Hodgson, passed away in October 2022. Known for his great generosity, his thoroughness and his sense of humor, he reached several generations of amateur and professional gardeners over his 40-year career. Thanks to his son, Mathieu Hodgson, and a team of contributors, will continue its mission of demystifying gardening and making it more accessible to all.

12 comments on “Tomato Hornworms Are Easy to Control

  1. Jo willson

    One or two worms per plant ???? I found at least 15 on the only plant I have. They ate one side of my green tomatoes. None had white eggs on their back so I killed them all. Is there a way to prevent them next year ??? TIA

  2. Disgusting they are. They were eating all my penta flowers. In two days I found 6 and 3 plants were ruined. I got the organic BT Thuricide spray and today found a dead worm. Gotta do it or they will eat all your ornamentals.

  3. Carla Dorey

    Well..I guess hornworms must consider Arkansas tomato plants as being prime
    real estate..? Because without fail every single summer that I have ever grown tomatoes..
    I have had to pick off at least five to even sometimes eight of those little agents of Satan hornworms off each of my plants!!!

  4. I discovered only one before I really knew what I was dealing with admiring it for its interesting beauty. I came back a couple of hours later and there were 4 or 5 on the same plant. Stay vigilant!

  5. I killed 20 on one tomato plant and 8 on another. I must have had the rarely, rarely type?

  6. I found a tomato worm which had what appeared to have dozens of tiny elliptical white eggs on it. What was I looking at>

    • That is a hornworm that has been attacked by a predatory wasp and the white things you see are the wasps eggs. Leave both alone, the wasps will help you get rid of the hornworms and the hornworm now being a host to the wasp larvae will die.

      • I thought the wasp would inject the eggs into the worms, they hatch and eat their way out. These wasps are much smaller than other wasps and don’t typically, sting humans.

  7. Pat Hayward

    Or better yet, plant an extra “sacrifice” plant (or 2) to relocate the caterpillars on to. This year we successfully removed 21 hornworms from our garden onto 2 sacrifice plants. After a week or so of feeding, I’m sure they made it into the soil to pupate and eventually emerge to become those magnificent sphinx moths we’re all in awe of.

  8. Pingback: The Moth That Flies Like a Hummingbird – Laidback Gardener

  9. Cold water, hey? I’ll try that….also found some on my sweet mint this year- yipes, I almost stuck it in my cold drink. We’d both be thrashing around then. :{

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