Caterpillar on a tomato plant? Who is it and what to do about it

If you’ve ever come across a caterpillar on a tomato plant, you know the trouble they can cause. Whether it’s a hole that goes straight through a ripening tomato or chewed leaves on tomato plants, tomato caterpillars disrupt harvests and gross out even the most unshakable gardeners. In this article, you’ll meet 6 different caterpillars that feed on tomato plants and learn what you can do to control them without using synthetic chemical pesticides.

What kind of caterpillars eat tomato plants?

There are several different types of caterpillars that feed on tomato plants both in vegetable gardens and in containers. Some of these caterpillars eat tomato leaves, while others feed on the developing fruits. I’ll introduce you to 6 tomato pest caterpillars later in this article but let me start by introducing you to the basic life cycle of all of these garden pests.

You’ll often hear them called “worms,” but when you find a caterpillar on a tomato plant it is not a “worm” at all, rather it is the larva of some species of moth. Moth larvae (like butterfly larvae) are technically caterpillars, not worms. Still, the term worm is often used in the common names of these insects.

Regardless of what you call them, the lifecycles of all tomato caterpillar pests are very similar. Adult moths are active from dusk to dawn, when the females lay eggs on host plants. The eggs hatch, and over a period of several weeks, the caterpillar feeds on the plant and quickly grows. If left to mature, most tomato pest caterpillars eventually drop to the ground where they burrow into the soil to pupate into adults. Some species have multiple generations each year.

When you find a caterpillar on a tomato plant, it may be a species that only feeds on tomatoes and other members of the nightshade family (like eggplant, peppers, potatoes, tobacco, and tomatillos). Other times, it may be a species that feeds not just on this plant family, but also on other vegetable garden favorites, like corn, beans, beets, and more. What particular plants you find a pest caterpillar on can help you identify it.

What to do when you find a caterpillar on a tomato plant

When you find a caterpillar on your tomatoes, your first task is to properly identify it. The best way to control any given pest depends on exactly which pest it is, so identification is key. There are several ways you can identify a pest caterpillar feeding on your tomatoes.

How to identify a caterpillar on a tomato plant

Aside from noting which plant species you find the caterpillar eating, there are a few other clues that lead you to a proper identification.

1. What kind of damage do you see?
   Thoroughly inspect your tomato plants to see where the damage is occurring and what it looks like. Sometimes a caterpillar on a tomato plant only eats the tomato itself, other times it eats the leaves.
2. Did the pest leave droppings behind?
   Since many pest caterpillars of tomatoes are green, it can be hard to spot them on the plant. But if you know what their droppings (called frass) look like, it is a clue to their identification. Many gardeners spy caterpillar frass before they see the caterpillar itself. Learning to identify a pest by its poop is surprisingly handy!
3. What does the caterpillar look like?
   Another piece of information that can lead to a proper tomato caterpillar ID is the insect’s appearance. Make note of things like:
   • How big is it?
   • What color is it?
   • Are there stripes or spots on the caterpillar? If so, where are they; how many are there; and what do they look like?
   • Is there a “horn” protruding from one end of the caterpillar? If so, what color is it?
4. What time of year is it?
   Some caterpillars don’t arrive on the scene until late in the summer, while others feed on tomato plants starting much earlier in the season. When did you first spy this pest on your tomato plant?

Once you’ve collected these essential pieces of information, identifying a caterpillar feeding on a tomato plant is a snap. Use the following insect profiles to help you with your ID.

Types of caterpillars that eat tomato plants

Here in North America, there are 6 primary pest caterpillars of tomatoes. These 6 species fit into three groups.

1. The hornworms. This includes both tomato hornworms and tobacco hornworms.
2. Armyworms. This includes the beet armyworm, the fall armyworm, and the yellow-striped armyworm.
3. The tomato fruitworm.

Let me introduce you to each of these tomato pest caterpillars and hand you some tips for making a proper ID. Then, well discuss how to control them.

Tobacco and tomato hornworms

These distinctive green caterpillars are the most infamous of tomato pests. They are large and unmistakable. Both tobacco hornworms (Manduca sexta) and tomato hornworms (Manduca quinquemaculata) feed on tomato plants and other members of the nightshade family, and one or both species are found in each of the contiguous 48 states, across much of southern Canada, and down into Central and South America.

Here’s how to tell the two species apart:

• Tobacco hornworms have a soft red spike (or “horn”) on their posterior. They have seven diagonal white stripes along each side.
• Tomato hornworms have a black horn on their rear end and eight sideways Vs running down both sides of their bodies.

Regardless of which species you’re dealing with, the hornworm caterpillar is a sight to behold. At full maturity, they are 4 to 5 inches in length, though they start out much smaller. Feeding damage occurs at the top of the plant first, in the form of missing leaves with just bare stems left behind. During the day, the caterpillars hide under the leaves or along the stems. They do most of their feeding at night.

Contrary to popular belief, tobacco and tomato hornworms are not the caterpillars of day-flying hummingbird moths which can often be seen drinking from flowers on warm summer afternoons. Instead, they are the larvae of night-flying moths known as hawk moths, which are a type of sphinx moth.

Hornworms leave distinctive droppings behind (see photo earlier in this article). Their dark green, rather large, pellets of excrement are often spotted before the well-camouflaged caterpillars are. When you spy the droppings, check your tomato plants carefully for the caterpillars.

Since the adult hawkmoth drinks nectar from tubular, light-colored flowers at night, avoid planting plants that produce these kinds of flowers near your tomato plants. This includes plants like nicotiana (flowering tobacco), jimsonweed, Datura, Brugmansia, and others. A few of these plants also serve as alternative hosts for hornworms.

Armyworms (yellow striped, beet, and fall)

Another pest you might find as a caterpillar on a tomato plant are the armyworms. There are three primary types of armyworms that sometimes take a liking to tomato plants. When fully grown, all armyworm species are about an inch and a half long. The adults of armyworms are brown or gray, nondescript moths that are active at night.

1. Yellow-striped armyworms (Spodoptera ornithogalli): These caterpillars are dark colored with a yellow band running down both of their sides. Just past the last pair of the legs at the front of their body, you’ll find a dark spot. Sometimes this caterpillar can be found feeding on tomato flowers and fruits in addition to the leaves. They also eat beans, beets, corn, peppers, potatoes, and other veggies.

   

2. Beet armyworms (Spodoptera exigua): When this pest caterpillar is young, it feeds in clusters of a dozen or so tiny caterpillars on the undersides of leaves. As they mature, they separate and go off on their own. There is a black spot on either side of the caterpillar’s body, just above their second pair of legs. Because they also feed on several common weeds in addition to beets, corn, broccoli, cabbage, potatoes, tomatoes, and other garden plants, try to keep the garden free of weeds. This pest does not survive freezing temperatures, though it migrates northward as the season progresses. By late summer, the beet armyworm may find its way as far north as Maryland on the east cost of the US. It is most problematic in warmer climates or in greenhouses and high tunnels.

   

3. Fall armyworms (Spodoptera frugiperda):  These caterpillars are striped with various shades of green, brown, and yellow. They appear mostly toward the end of the growing season. Their eggs are found in tan-colored clusters. Armyworms are more problematic in warm, southern growing regions as they do not survive freezing temperatures, but like beet armyworms, they migrate northward as the season progresses. Fall armyworms are problematic on turfgrass, and they also feed on several hundred species of plants, including tomatoes, corn, beans, beets, peppers, and other vegetables.

   

Tomato fruitworms

Also known as the corn earworm, tomato fruitworms (Helicoverpa zea) are the larval stage of a nocturnal moth. If they feed on tomatoes, they are called tomato fruitworms. If they feed on corn, they’re called corn earworms. But both are the same species of insect. Tomato fruitworms feed on the developing fruits of tomato, eggplant, pepper, and okra plants. This pest does not overwinter in cold climates, but it migrates northward as the season progresses. Female moths lay eggs on host plants. The eggs hatch and begin to feed. Tomato fruitworms come in a huge range of colors, depending on what they are feeding on. These caterpillars can be green, brown, gray, beige, cream, black, or even pink. They have alternating light and dark stripes down their sides, and there can be several generations each year.

Tomato fruitworms tunnel into tomatoes, leaving round holes through the skin. Often there is both an entrance hole and an exit hole present. The inside of the tomato turns to mush and frass (excrement) is found inside the feeding tunnel.

How “good bugs” help control these tomato pests

Beneficial insects such as ladybugs, green lacewings, big eyed bugs, and minute pirate bugs love to feast on all of these species of pest caterpillars, particularly when the caterpillar is small. Spined soldier bugs are another predator of all of these tomato pests. Plant lots of flowering plants in and around your vegetable garden to attract and support these beneficial insects. If you are growing a large number of tomatoes, consider releasing a parasitic wasp known as the Trichogramma wasp that parasitizes the eggs of these and other pest moth species.

When not to worry about a caterpillar on a tomato plant

There is another species of beneficial insect that helps control tomato and tobacco hornworms. It is a parasitic wasp known as the cotesia wasp (Cotesia congregata), which is a member of the family of braconid wasps. Evidence of this predator is a frequent sight in backyard vegetable gardens. If you ever come across a tomato or tobacco hornworm with what looks like white grains of rice hanging off its back, please do not kill the caterpillar. Those rice-like sacs are the pupal cases (cocoons) of the cotesia wasp.

Females lay from a few dozen to a few hundred eggs just beneath the skin of a hornworm caterpillar. The larval wasps spend their entire larval life stage feeding on the inside of the caterpillar. When they are ready to mature, the emerge through the skin, spin their white cocoons, and pupate into adults. If you destroy the caterpillar, you’ll also be destroying another generation of these very helpful wasps.

How to get rid of a caterpillar on a tomato plant

If you still have troubles with pest caterpillars despite encouraging all of their natural predators, there are several things you can do when you spy a caterpillar on a tomato plant and it is causing significant damage. After you identify the pest, it’s time to take action. Start with hand-picking. If it’s just a few tomato hornworm caterpillars, they are easy to pluck off and there’s no need to turn to pesticides. The same goes for a small number of armyworms. Drop them into a jar of water with a teaspoon of dish soap, squish them, or feed them to your chickens.

Products to control tomato pest caterpillars

If you want to protect a large number of tomato plants from these caterpillar pests, there are two organic spray products you can use.

1. 1. Bt (Bacillus thuringiensis): This bacterium is sprayed onto plants. When a caterpillar feeds on that plant, the Bt disrupts its feeding and the caterpillar dies. It is only effective against the larvae of moths and butterflies and will not affect non-target insects or beneficials. However, spray Bt only on a windless day to ensure it doesn’t drift onto butterfly host plants such as violets, dill, parsley, or milkweeds.
   2. Spinosad: This organic pesticide is derived from a fermented soil bacterium. Though it is seldom called for unless infestations are severe, Spinosad is effective against these pest caterpillars. Avoid spraying it when pollinators are active.

With these tips for identifying and controlling pest caterpillars on tomato plants, big yields and delicious tomato harvests are just around the corner!

For more information on growing a bumper crop of juicy tomatoes, please visit the following articles:

• How to make tomato plants grow faster
• Supporting tomato plants
• Tomato pruning mistakes to avoid
• Tomato growing secrets from a pro
• When to pick tomatoes for the best flavor
• Companion plants for tomatoes
• How often to water tomatoes
• What to do with tomato suckers

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