Green Caterpillars on Tomato Plants (Tomato Hornworms) – Identification and Control

The tomato hornworm is a large green caterpillar with a horn-like tail that does tremendous damage to tomato plants. The hornworms have distinctive creamy-white V-shaped markings along their sides. However, the destructive caterpillars can be challenging to spot on tomato plants because their green color blends in with tomato foliage.

Getting rid of tomato hornworms for good isn’t easy. It takes patience and vigilance to spot the giant fat green worm-like insects. Usually, handpicking the caterpillars and dropping them in soapy water is the most effective way to eradicate them. However, there are several ways to prevent tomato hornworms or control their numbers.

This article is a guide to identifying fat green caterpillars that damage tomato plants. Pictures and descriptions of the pale green hornworms will help spot them before they do too much damage. In addition, you’ll get handy tips on getting rid of hornworms for good.

How to Identify Tomato Hornworms (Manduca quinquemaculata)

Tomato hornworms are large caterpillars with green bodies, a bluish black tail-like horn, and white V-shaped marks along each side. The plump green hornworms can measure up to 5” (127 mm) long. They also have five pairs of large prolegs on their central segments and an enlarged head curled inward.

Tomato hornworms get their name from the black or dark blue pointed protrusion at their tail. The color of this tail-end helps to tell the tomato hornworm apart from the related tobacco hornworm. The tail of the tomato hornworm is dark blue, whereas the tobacco hornworm has a reddish, horned tail.

Another way to identify the pale green tomato hornworm is the V-shaped yellowish-white marking along its sides. Close up, you’ll notice small eye-like markings in the apex of the white V-shape. There are also eyespots on either side of its head to help ward off predators.

Tomato hornworms can be challenging to identify on plants because they blend in well with their environment. However, if you spot one under the leaves or crawling on the stems, you can safely remove the caterpillar by hand.

Tomato hornworms are harmless and won’t sting you, despite their stinger-like tail, and they are not venomous to humans.

Tomato Hornworm Vs. Tobacco Hornworm

Visually, the tomato hornworm (Manduca quinquemaculata) and the tobacco hornworm (Manduca sexta) look similar. The differences are in tail color and distinctive markings. Rather than a reddish horn tail, the tail of the tomato hornworm is dark blue-black. Also, the tobacco hornworm has diagonal lines on its side, not a chevron shape like the tomato hornworm.

Life Cycle of Tomato Hornworms

The tomato hornworm life cycle consists of four phases — egg, caterpillar (larva), pupa, and adult moth. The eggs hatch about seven days after the female lays them. From when the caterpillars hatch until they are full grown it takes around four weeks, and the adult moths live for 10 to 30 days.

Hornworm eggs are tiny, pale green to white oval balls measuring around 0.039” (1 mm). Once the eggs hatch in late spring, the larvae start feeding on tomato plant leaves. They go through five instars (growth stages), during which they shed their skin and grow up to 4” or 5” (100 – 127 mm).

During the larval stage, tomato hornworms generally stay on the same plant, devouring the leaves thanks to their voracious appetite. Through most of the larval stages, the tomato hornworm retains its identifying features — creamy white V-markings and a black horn tail.

The third stage of the tomato hornworm life cycle is when it goes underground to pupate. The pupa is a large, reddish-brown segmented cigar-like object with a loop at one end. After emerging from the pupa, the tomato hornworm turns into the five-spotted hawkmoth. This large brown and gray moth has a wingspan of 5” (13 cm).

Tomato Hornworm Damage

As their name suggests, the tomato hornworm favors tomato plants and can quickly devour leaves on an entire plant. Sometimes, the destructive pests may attack the fruit, leaving large scars on tomatoes. However, these ravenous caterpillars will also gorge on eggplant, potato, tobacco, and pepper leaves — all plants from the nightshade family Solanaceae.

However, it’s good to note that tomato hornworms are not dangerous to humans. You can safely pick them up without fear of being stung. Additionally, despite their insatiable appetite, the green hornworms won’t bite humans, and their black tail isn’t a stinger. Therefore, physically removing them is the best way to prevent damage.

But how can you tell if tomato hornworms are attacking your greenhouse crops? Here are some tell-tale signs that the large caterpillars are devouring your tomato plants.

Tomato hornworms destroy leaves

The first sign of tomato hornworm damage is holes appearing in your tomato plant leaves. This usually occurs in late spring, just after the harmful larvae have hatched. Unfortunately, the pesky caterpillars are hard to spot after they have hatched because they are so tiny.

As they grow, the plant-destroying “bugs” strip the upper leaves on a tomato plant until only the stems remain. Other evidence of tomato hornworm activity is devoured flowers, complete defoliation, and open wounds on tomato fruits. The hungry caterpillar can consume a 1-ft. (30 cm) long tomato leaf in a day.

Tomato hornworm droppings

Droppings from tomato hornworms look like dark green or black dry, crumbly barrel-shaped substances. The tomato hornworm poop resembles tiny coffee beans or small black pellets. If the hornworms are causing damage, you’ll find the black or green droppings on the top of the leaves.

Tomato hornworm damage fruits

Unfortunately, not even your prized tomatoes — ripe or unripe — are safe from tomato caterpillar damage. Caterpillars, in their final instars, may start eating tomatoes. They will eat away the skin and some of the flesh, leaving behind large, deep scars on tomatoes. A large tomato hornworm can devour several tomatoes in a short time.

How to Protect Plants From Tomato Hornworms

Prevention is critical when it comes to protecting tomato plants from the destructive effect of hornworms. For example, it’s vital to check tomato leaves for signs of eggs and then wipe down the leaves to remove them. However, this may not always be successful because the small pale oval eggs are exceedingly tiny.

The most common way to protect tomatoes from caterpillar activity is to check the plants every few days for the nasty bugs. Despite their camouflage, they should be easy to locate due to their large size.

How to Control Tomato Hornworm

Keeping tomato hornworms away from your greenhouse crops and tomatoes requires a multi-faceted approach. In most cases, it’s best to control tomato caterpillar populations using natural methods. This reduces exposure to harmful and toxic chemicals and prevents the voracious larvae from building up resistance to pesticides.

Here are some effective methods that many gardeners have found helpful in controlling tomato hornworms.

Beneficial insects are effective for tomato hornworm control

Predatory insects like ladybugs, green lacewings, trichogramma parasitic wasps, and braconid wasps are effective in controlling hornworm numbers. The beneficial insects prey on caterpillar eggs and larvae, devouring them before they get a chance to do damage.

Other beneficial insects parasitize tomato hornworms. For example, parasitoid wasps lay their eggs inside larvae. The eggs hatch inside the caterpillars and then feed on the hornworm’s inside until they pupate. The larval pupae look like little grains of white rice stuck to the caterpillar. Once the adult wasps hatch, they kill their host — the dreaded tomato hornworm.

Therefore, if you see a tomato hornworm on your plants and have many tiny white sacs attached, it’s best to leave the caterpillar alone. The parasitoid wasps will soon hatch and kill the weakened caterpillar. They will then search out other caterpillars to parasitize and help keep your plants free from hornworms.

Have good weed control practices to control tomato hornworms

Tilling the soil in the fall is a highly effective way to eradicate tomato hornworms from your yard. This control method is helpful because caterpillars burrow into the ground after harvest to overwinter. Tilling after you have harvested your tomatoes and before you plant new ones will disrupt the caterpillar’s life cycle, destroying most of the larvae in the ground.

Crop rotation for tomato hornworm control

A tried and tested method for organic pest control is to rotate crops every other year. This cultural control method is beneficial if you were plagued by tomato hornworms the previous year. Then, all you need to do is plant your tomatoes in a new location. This helps prevent overwintering hornworms from emerging too close to plants to lay their eggs.

Mulch can help prevent tomato hornworm larvae from emerging

A thick layer of mulch around your newly-planted tomato plants can help keep the destructive caterpillars at bay. The mulch helps prevent the larvae from emerging from the soil and laying eggs on your nightshade plants. Some gardeners recommend black plastic to create a solid barrier. Alternatively, you can lay down a thick layer of straw.

Mulching also has a beneficial effect on your crops in general. First, the layer of organic mulch can help keep the ground cool, aid moisture retention, and prevent weeds from emerging. Of course, you also have the added benefit of controlling nasty bugs that overwinter in the soil.

How to Get Rid of Tomato Hornworms

The easiest way to eradicate large fat tomato caterpillars from your plants is to remove them by hand. However, there are also ways to kill off tomato hornworms during most stages of their life cycle. For example, natural insecticides like bacillus thuringiensis, neem oil, and insecticidal soap can be effective against hornworm eggs and emerging larvae.

Handpick tomato hornworms to eradicate them

Removing tomato hornworms by hand is usually the easiest way to kill them. Despite their pale green appearance acting as camouflage, you can generally spot the huge bugs during a careful inspection. Hornworms are harmless and won’t sting or bite. Pick each one up and drop it into a bucket of hot soapy water to destroy them.

Check for tomato hornworms twice weekly to limit plant damage in your greenhouse or yard.

Neem oil kills tomato hornworm eggs and tiny larvae

Spraying neem oil can be one of your practical tools in your battle with the green beasties. Neem oil works on bugs because it contains a natural insecticide that disrupts a caterpillar’s life cycle. Neem oil spray inhibits larvae development and growth. In time, the caterpillar eggs and larvae die.

To apply neem oil to your tomato plants, combine 2 tsp. neem oil and 1 tsp, liquid Castile soap with 1 quart (1 l) of water. Mix the neem oil solution well in a spray bottle and liberally douse your tomato plant leaves. Apply the natural pesticide every seven days until all signs of caterpillar activity have disappeared.

For neem oil to be effective, you should start using it early in the season to target tomato hornworm eggs and the emerging larvae. However, combining the neem oil spray with other hornworm control methods is vital if you want to eliminate the caterpillars from tomato plants completely.

Insecticidal soap kills tomato hornworms

Spraying insecticidal soap is another effective way to kill tomato hornworms. Insecticidal soap is a natural bug control method that works by suffocating small larvae and breaking down their protective outer layer. This way, the soap residue helps to dehydrate the caterpillars, resulting in their death. In addition, using insecticidal soap is effective for wiping down tomato plant leaves to remove eggs.

You can make the soap spray using a brand like Dr. Bronner’s or Ivory Snow. You should use up to three tablespoons for every gallon (3.4 l) of liquid. After combining the soap and water, spray the solution on both sides of the leaves and spray any visible caterpillars. Insecticidal soap must come into contact with the pests to be effective.

Alternatively, you can buy commercially produced organic insecticidal soap for tomato hornworm eradication.

Bacillus thuringiensis (Bt) gets rid of tomato hornworms

Using a low-risk natural pesticide like bacillus thuringiensis (Bt) can help get rid of pesky tomato caterpillars for good. The bacteria strain to use is Bacillus thuringiensis var. kurstaki which targets caterpillars. You buy the Bt solution and follow the manufacturer’s instructions for application.

Bacillus thuringiensis is a naturally occurring soil bacteria that won’t harm your plants and other insects. It only works if the tomato hornworms ingest the solution and it’s most effective on caterpillars less than 2” (50 mm) long. Therefore, you should spray the tomato plant foliage with the solution, especially the underside of the leaves for best results.

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