Mahedi Hasan

How Many Tomato Hornworms Per Plant: Debunking Common Myths.

A tomato plant can have anywhere from one to a dozen tomato hornworms feeding on it. Tomato hornworms are common pests that can quickly destroy tomato plants if not detected and managed promptly.

These large, green caterpillars with white markings consume leaves and fruits of tomato plants and other members of the nightshade family. The damage caused by the tomato hornworm includes defoliation, scarring and cosmetic damage to fruits. A single hornworm is capable of causing significant damage to a tomato plant.

If left unchecked, one caterpillar can easily grow into a large population that can ruin an entire crop. It is important to inspect tomato plants regularly for any signs of tomato hornworms and take necessary steps to control their population.

How Many Tomato Hornworms Per Plant: Debunking Common Myths.


Introducing Tomato Hornworms

Tomato hornworms, known scientifically as manduca quinquemaculata, are a type of caterpillar that feed on plants in the nightshade family, including tomatoes, peppers, and eggplants. These pests can cause extensive damage to plants and crops if left unchecked, making it important for gardeners and farmers to understand their behavior and lifecycle.

Definition And Appearance Of Tomato Hornworms

  • Tomato hornworms are large, bright green caterpillars that can grow up to 4 inches in length.
  • They have white stripes on their sides and a prominent horn-like protrusion on their rear end, hence the name ‘hornworms’.
  • They often blend in with the leaves of plants, making them difficult to spot.

Life Cycle And Habitat

  • Tomato hornworms typically lay their eggs on the underside of leaves in the late spring or early summer.
  • Once hatched, the caterpillars feed on plant foliage and can cause rapid damage if not managed.
  • After about a month of feeding, they burrow underground to pupate and emerge as moths in 2-3 weeks.
  • The adult moths are brown with white spots and can often be seen around dusk.

General Overview Of The Importance Of Tomato Hornworms In The Ecosystem

While tomato hornworms can be detrimental to crops, they do play a role in the ecosystem. They are important food sources for birds and other insectivores and their presence can help regulate the populations of other insect pests. In addition, they have been studied for their medicinal properties and have been found to have potential antifungal and antibacterial activity.

Thus, it is important to find a balance between their impact on crops and their role in the larger ecosystem.

Myth 1: The More Tomato Hornworms, The Better

Are you under the impression that the more tomato hornworms there are on a determinate tomato plant, the better it is for the plant? This widespread myth has been debunked, and in this section, we will explain why.

Explanation Of The Myth

The idea of having multiple tomato hornworms devouring a tomato plant might seem plausible, but it’s not accurate. The myth stems from the fact that tomato hornworms are predators of other insects, which could potentially eat the plant. However, the truth is that the damage caused by the hornworms outweighs any positive benefits.

Analysis Of The Pros And Cons Of Having Many Tomato Hornworms

Let’s take a closer look at the pros and cons of having multiple tomato hornworms on a plant:


  • Tomato hornworms are predators of other insects, such as aphids and spider mites.


  • Tomato hornworms can be voracious eaters, causing severe damage to the plant and reducing yield.
  • Tomato hornworms are difficult to spot due to their green color and the fact that they tend to blend in with their surroundings.
  • Tomato hornworms can leave behind fecal matter that attracts other pests and diseases.
  • Tomato hornworms have a high reproductive rate, which means that they can multiply quickly and cause more damage to the plant.

Supporting Evidence And Research On The Impact Of Having Too Many Tomato Hornworms On Plants

Research has shown that tomato hornworms can have a detrimental impact on tomato plants. Here are some findings:

  • A study conducted by the university of illinois found that a single tomato hornworm can defoliate an entire plant if left untreated.
  • Another study found that an infestation of tomato hornworms reduced tomato production by up to 15%.
  • Tomato hornworm feeding can lead to plant stress, making them more susceptible to diseases and other pests.

The myth that a higher number of tomato hornworms is beneficial for tomato plants is unfounded. Tomato hornworms are indeed natural predators of other insects, but their feeding habits and high reproductive rate can cause severe damage to the plant.

It’s important to monitor and manage any infestations to prevent detrimental effects to your tomato plants.

Myth 2: Tomato Plants Can Only Tolerate A Few Hornworms

Tomatoes are a staple in many gardens, and it is common knowledge that certain pests can put a strain on their yield. One of the most notorious bugs known to cause damage to tomato plants is the tomato hornworm. There are several myths surrounding tomato plants’ tolerance towards hornworms, and this section will concentrate on one of them.

Myth 2: Tomato Plants Can Only Tolerate A Few Hornworms.

It is a common misconception that only a few hornworms will not have a significant impact on tomato plants. However, the truth is that the tolerance level of tomato plants towards hornworms varies depending on several factors.

Factors affecting the tolerance level of tomato plants towards hornworms:

  • The stage of the plant: Young tomato plants can be severely affected by just a few hornworms, while mature plants may be able to withstand their presence.
  • Number of hornworms: The greater the number of hornworms, the higher the damage they cause to the plant. Moreover, the more hornworms there are, the greater the competition for food sources.
  • Environmental conditions: Factors such as temperature, humidity, and rainfall can significantly affect a plant’s tolerance level towards hornworms. For instance, high temperatures and low humidity levels tend to increase the tomato plant’s susceptibility to damage by hornworms.

Scientific studies and research to verify impact:

Many scientific studies have been conducted to verify the impact of tomato hornworm infestations on plant yield. Indeed, hornworms are known for their devastating effect on crops since they are voracious eaters. The following are some of the findings from these studies:

  • Reduced yield: Hornworms can significantly reduce the yield of tomato plants they infest. One study found that hornworm infestations could reduce the yield of tomato plants by up to 70% (1).
  • Indirect effects on plant health: In addition to directly feeding on tomato plants, hornworms can also cause indirect damage by transmitting diseases. For instance, hornworms that feed on infected plants can spread plant viruses among tomato plants (2).
  • Timing of infestation matters: Plant damage caused by hornworms is most severe when the infestation occurs at specific plant growth stages. For example, it is more damaging when hornworms infest plants when they are at the flowering stage than at the fruiting stage.

The myth that tomato plants can only tolerate a few hornworms is false. The tolerance level of tomato plants towards hornworms varies depending on several factors, including the plant’s stage, the number of hornworms, and environmental conditions. Scientific studies have shown that hornworms can cause significant damage to tomato plants, reducing their yield and indirectly affecting their health.

As such, it is essential to take measures to prevent and control hornworm infestations, such as using natural predators, manual removal, or organic insecticides.


  • Cavanagh, a. (2021). Tomato hornworm – biology and control. University of missouri integrated pest management. Retrieved from https: //
  • Srinivasan, r., & alvarez, j. m. (2016). Tomato hornworm (manduca quinquemaculata) feeding damage (tobacco hornworm (m. sexta) and silverleaf whitefly (bemisia tabaci) infestations) on yield of fresh-market tomatoes grown in raised-bed and conventional tillage systems. The journal of cotton science, 20(3), 285-297.

Reality Check: The Optimal Number Of Tomato Hornworms Per Plant

Tomato hornworms are a common problem among home gardeners. These voracious caterpillars can do significant damage to tomato plants, leading to yield losses. The optimal number of tomato hornworms per plant can vary depending on several factors. In this section, we will discuss the ideal number of tomato hornworms per plant, factors to consider when determining the optimal number, and case studies of typical tomato hornworm infestations.

Explanation Of The Ideal Number Of Tomato Hornworms Per Plant

  • The ideal number of tomato hornworms per plant is zero. These caterpillars can strip a tomato plant of its leaves and even feed on the fruit. Ideally, you want to prevent these pests from ever infesting your tomato plants.

Factors To Consider When Determining The Optimal Number

  • The size of the tomato plant: In general, larger tomato plants can tolerate more hornworms than smaller plants.
  • The stage of the growing season: Younger plants are more vulnerable to hornworms than more established plants.
  • The level of infestation: If you notice a few hornworms on a plant, you may be able to remove them by hand or with insecticidal soap. However, if the plant is overrun, you may need to take more significant measures.
  • Your tolerance for damage: Some gardeners may be more willing to tolerate some amount of damage to their plants than others.

Case Studies Of Typical Tomato Hornworm Infestations And Their Effects On Tomato Yield

  • In a case study conducted by the university of illinois extension, tomato plants with no hornworms produced an average of 18.5 pounds of fruit per plant. In contrast, plants with 10 hornworms produced just 8.5 pounds, a roughly 54% reduction in yield.
  • Another study conducted in california found that a plant with five hornworms had a 75% reduction in fruit yield compared to a hornworm-free plant.

The ideal number of tomato hornworms per plant is zero. However, if you do find yourself dealing with an infestation, it’s essential to consider the size of the plant, the stage of the growing season, the level of infestation, and your tolerance for damage.

Keeping these factors in mind can help you determine the optimal number of hornworms for your tomato plants.

Managing Tomato Hornworm Infestations

Tomatoes are a staple crop in many gardens, but they’re vulnerable to pests like the dreaded tomato hornworm. These pests are green and brown caterpillars that can grow up to four inches long and feast on tomato plants. Here are some best practices and strategies for controlling hornworm infestations, along with natural and chemical methods for controlling these pests, and prevention tactics and post-infestation management.

Best Practices And Strategies For Controlling Hornworms

  • Inspect plants regularly and remove any hornworms by hand.
  • Invite natural predators to your garden, like birds or parasitic wasps, by planting companion plants like marigolds or parsley.
  • Provide shade for your tomatoes to boost their defenses against hornworms.
  • Use row covers to protect newly planted seedlings.

Natural And Chemical Methods Of Controlling Hornworms

Natural methods:

  • Handpicking: If there are only a few caterpillars visible, you can easily remove them by hand.
  • Beneficial insects: Beneficial insects, such as ladybugs, green lacewings, or predatory wasps, can eat many insects, including the hornworm.
  • Garlic spray: Make a garlic and water solution to spray on your tomato plants. The garlic scent repels the hornworm and other insects.

Chemical methods:

  • Bacillus thuringiensis (bt): Bt is a bacterium that affects the hornworm’s digestive system, making it impossible for them to eat.
  • Spinosad: A natural soil bacterium that is toxic to hornworms, but harmless to humans and beneficial insects.

Prevention Tactics And Post-Infestation Management

Prevention tactics:

  • Rotate your crops and avoid planting tomatoes in the same area every year.
  • Keep your garden weed-free, as weeds can attract pests.
  • Keep garden tools clean and tidy, and avoid sharing between gardens to prevent spreading any pest infestation.

Post-infestation management:

  • Dispose of any infected plants, to prevent the spread of the infestation.
  • Clean and sanitize any gardening tools that may have been in contact with infected plants.
  • Consider using organic insecticides as needed, to prevent future infestations.

Remember that while controlling tomato hornworms can be challenging, it’s not impossible! Utilizing a combination of best practices, prevention tactics, and natural and chemical insecticides can help you keep your tomatoes healthy and free from pests.

Frequently Asked Questions For How Many Tomato Hornworms Per Plant

How Do You Identify Tomato Hornworms On Plants?

Tomato hornworms are green caterpillars with white stripes and can grow up to 4 inches long. They can be found on the stems and leaves of tomato plants, and they eat the foliage, leaving large holes.

Are Tomato Hornworms Harmful To Tomato Plants?

Yes, tomato hornworms are harmful to tomato plants because they eat the foliage, leaving large holes and defoliating the plant. This can reduce the plant’s ability to produce fruits and result in stunted growth.

How Many Tomato Hornworms Are Typically Found Per Plant?

The number of tomato hornworms found per plant can vary depending on the size of the plant and the severity of the infestation. In general, it’s common to find 1-2 tomato hornworms per plant, but an infested plant can have up to 6-8.

How Do You Control Tomato Hornworms On Plants?

To control tomato hornworms, you can handpick and remove them from the plant. You can also use natural predators like parasitic wasps or bacillus thuringiensis (bt) insecticides. Planting herbs like garlic, basil, and cilantro can also help repel them.

What Is The Lifecycle Of A Tomato Hornworm?

Tomato hornworms hatch from eggs laid on tomato plant leaves. They then go through several instars, molting and growing, until they reach full size. They then pupate in the soil and emerge as a large moth, which lays eggs to start the cycle over again.


As we wrap up the discussion on how many tomato hornworms per plant, it is clear that these pests can easily cause significant damage to the tomato plants if not controlled adequately. Taking care of these tiny green caterpillars is crucial, especially as they can reproduce faster than expected and spread quickly to infect other plants.

By following the various methods outlined in this blog post, such as handpicking, utilizing natural predators, using insecticides, and preventive measures, you can protect your tomato plants from the hornworm invasion. Also, remember to keep a keen eye on your plants, and regularly scout for signs of hornworm attacks.

Consistency is key when it comes to managing tomato hornworms and other pests that may pose a threat to your garden. With adequate knowledge and effective control methods, you can ensure a healthy crop and a bountiful harvest.