Pest Profiles: Tomato Hornworm

As the gardening season progresses, we all have to be alert and ready to tackle those annoying little insects that can decimate our crops and leave us devastated that all the hard work we put into growing our fruit and vegetables was a waste of time and money. For many growers, one of the evilest – and ugliest, is the caterpillar known as the tomato hornworm which, despite its name, doesn’t just destroy tomatoes. They are partial to many different plants including tomatoes, peppers, potatoes, tobacco, and eggplant.

The caterpillar is the larvae of the five-spotted hawkmoth (Manduca quinquemaculata) and is found in almost every region of the US.

These caterpillars happily eat their way through the leaves of the plants as well as the stems and even the unripened fruit, destroying entire crops. The tomato hornworm can cause extreme damage to your plants overnight.

Tomato Hornworm
Source: Flickr User Mike Lewinski

Identification

Once you see and recognize your first tomato hornworm, you won’t forget it. They are probably one of the largest caterpillars you will see and measure 4 inches in length. Young tomato hornworms are yellowish-white in color and have no distinctive markings. As the caterpillars grow, they turn a pale green with white V-shaped marks on their body. They have a black projection, or horn, on the last segment of their body. Once the caterpillar develops into a moth, it turns either gray or brown in color and has a wingspan of 5 inches. The wings have white stripes on them, and the body is sometimes covered in brown or orange spots. The moth flies at great speeds and is sometimes known as the hummingbird moth due to its ability to hover like the hummingbird.

The caterpillar blends in well with the green leaves on a plant. You need to check your plants daily. The best time to spot these pests is early morning and in the evening. They dislike extreme heat, so cool days, early morning, and late evening onward is when most of the damage is done to the plants. Look for dark green droppings on the top leaves of the plants. Underneath the leaf is the most likely place you’ll find a hornworm. Plants attacked by tomato hornworm have stems with leaves stripped bare as well as wilted leaves.

Life Cycle

The female five-spotted hawkmoth lays its eggs after mating on the underside of both lower and upper leaves on a plant. The eggs are smooth and light green and they hatch within 5 days. As soon as the caterpillars hatch, they begin to devour the plants and reach maturity in four weeks. Once the caterpillars are fully grown, they drop off the plant and burrow into the soil to pupate. Two weeks after this, the moth emerges and a second generation begins. Once the second generation pupates, they stay in the soil throughout the winter months.

Removing and Preventing Tomato Hornworm Naturally

The easiest way to remove the hornworm is to pick it off. They cannot sting you and dropping them in a bucket of soapy water kills the caterpillars quickly. Insects such as ladybugs and lacewings will attack the eggs. Till the soil at the beginning and the end of the gardening season.  As the pupae are not very deep in the soil, tilling successfully disrupts the life cycle of the caterpillar. Tilling gets rid of approximately 90% of the tomato hornworm pupae found in the soil. 

The larvae of predatory wasps feed on the tomato hornworm and help you to control the caterpillar population naturally. Wasp larvae are seen on the back of the hornworm and resemble grains of rice. Don’t rush to remove this larvae, as it doesn’t hurt your plants, but does kill the pesky caterpillars.

Tomato Hornworm


Plant herbs such as dill and basil near your tomatoes as they are a great companion plant and keep the hornworm as well as many other insects away.

Use light traps in your garden to trap the moths. The moths are drawn to the light and then get trapped, preventing them laying eggs on your plants.

Now you know how to spot and control tomato hornworm naturally, read our article on how to control slugs the natural way, too. Keeping insect populations under control naturally helps you maximize crop yield without resorting to the application of harmful chemicals.

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Post Author: Becky Britton

2 thoughts on “Pest Profiles: Tomato Hornworm

    Indrani

    (July 8, 2017 - 3:33 pm)

    Incredible capture of the caterpillar. Love the little details. Never knew those wasp larve feed on them.
    I will watch out for these in my garden.

      Katy Willis

      (July 10, 2017 - 5:43 pm)

      Yes, wasps aren’t everyone’s favorite creature, but predatory wasps are really useful in the garden.

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