If you’re a gardener, then you’ve likely seen creepy-looking tomato hornworms and know they can be devastating to your garden. These caterpillars can devour your tomatoes in no time, and they’re hard to get rid of. Learn how to easily find, kill, and prevent tomato hornworms naturally so that you can keep your garden healthy, productive, and pest-free. Let’s get started!
About Tomato Hornworms
The five-spotted hawk moth, aka sphinx moth, lays the tomato hornworm egg. Its scientific name is Manduca quinquemaculata.
- They are large, thick-bodied insects with narrow front wings.
- They are mottled gray-brown with yellow spots on the sides of their body.
- The mature moth has a wingspread of four to five inches.
- There are alternating light and dark bands on their larger hind wings.
If you see moths flying around in your garden, you can be certain they have laid eggs. Begin looking for the teeny-tiny hornworms.
- Tomato hornworms are large caterpillars with horn-like projectiles growing on their tails.
- Their favorite plant in your garden is the tomato.
- Hornworms can ravage a plant overnight eating all of its leaves.
- They also eat the tomatoes, large and small.
- Physical removal is the most effective way to protect plants.
Their Plants of Choice: The Nightshade Family
- Bell Peppers
1.Do tomato hornworms bite or sting?
Tomato hornworms are not poisonous to humans in spite of their frightening appearance. The horn-like projection isn’t sharp enough to pierce the skin.
When you pick up a hornworm, it may wrap around your finger and cling to your skin—an odd sensation that is sometimes unpleasant but not hazardous. Just a little icky.
2. How long do hornworms live?
The larvae of these species hatch in late spring or early summer. Over a period of three to four weeks, they go through five molts before becoming full-sized adult worms. Then they drop off the plant and burrow into the soil to form their cocoon and transform into moths.
If it’s warm enough, there will be a first generation that matures into moths and lays a second generation that will overwinter in the soil of your garden. In the spring, the hibernating cocoons of this second generation will hatch and moths emerge from their holes. They lay eggs beginning the whole cycle over again.
3. Are there plants that repel hornworms?
While the plants themselves don’t repel the hornworms, dill, clover, fennel, and sweet alyssum attract parasitic wasps that feed on hornworms.
There are also some companion plants you can consider to discourage them from laying eggs. For more on this, see the section later in this article.
How to identify tomato hornworms
- Hornworms ((Manduca quinquemaculata) are among the largest caterpillars in the garden and can measure up to five inches in length on average.
- Although, I have seen them larger! The largest one we’ve ever had was just over 7″ long!
- The newly hatched hornworms are yellow to white in color with no markings. These are very hard to see and they quickly become green to blend in with the garden veg.
- During the molting process, they develop eight white, V-shaped marks on each side.
- Tomato hornworms have a black horn-like protrusion on their last segment.
Tomato vs. Tobacco Hornworms
There are a few species of hornworms that inhabit North American gardens, including tomato hornworms (Manduca quinquemaculata) and tobacco hornworms (Manduca sexta). Here’s how to tell them apart:
- Tobacco hornworms have parallel white stripes, while tomato hornworms have white V-shaped markings.
- The black markings on the tobacco hornworms’ stripes run along each of them but tomato hornworms’ markings do not.
- The rear end of a tobacco hornworm has a red “horn,” whereas that of a tomato hornworm is black.
The life cycle of tomato hornworms
- In the early to mid-spring, adult moths lay eggs on the underside of leaves. They are so tiny it’s almost impossible to see them.
- In only a week a hatch! They immediately begin eating the leaf they were hatched on.
- They continue to consume your nightshade plants, especially tomatoes, for 4–6 weeks. During the first 3-4 weeks, they pass through 5 molts until they are adult caterpillars.
- Once they’re adults they continue eating for a couple of more weeks before it drops from the plant, burrows into the soil, and turns into a pupa.
- If it’s warm enough, this first generation will mature into moths which lay a second generation that will overwinter in the soil.
- In the spring, the hibernating cocoons of the second generation will hatch and moths emerge from their holes. They lay eggs beginning the whole cycle over again.
- If the summer is not sufficiently hot or long in your growing zone, there will be only one generation. They will overwinter in the soil and emerge in the spring and begin the cycle again.
Crop Damage and Destruction
Tomatoes are the plant of choice for these creepy-crawly critters. But they can also be found on other members of the nightshade family.
The tomato hornworm eats the leaves, stems, and fruit of the host plant. Because they’re so difficult to spot among the leaves, they are often mature and have done major damage before you know they’re there.
The adult caterpillar consumes roughly the same amount as all of the previous 4 stages combined! Large hornworms can strip multiple stems of their leaves and consume a medium-size tomato overnight.
How to Easily Spot Hornworms
Check your plants for tomato hornworms in the early morning just as the sun comes up or late evenings at dusk. I check them at least every other day because they grow so quickly and are so easy to miss.
I do a visual check as described below but the most effective way I have found is using the Pro Tip below.
The first way is to look for the dark green or black droppings (poop) they leave behind as they eat. This is easy to see and lets you know they are there. When you spot it, examine the leaves and stems above the droppings. You will likely find your culprit on the underside of leaves above the poop.
Look for stems with leaves missing and drooping leaves. They may be found nearby.
Tomato hornworms are great at camouflage but become easier to find as they grow in size and leave larger areas of damage in their wake.
Pro Tip To Defeat Them
A dear friend of mine taught me this trick. Using a black light flashlight, go out to the garden when it’s dark.
You can go at night if you’re a night owl like my friend, or early morning if you’re like me and are up at 4:30 in the morning.
Turn the flashlight on and you will find glowing things in your garden. A tomato hornworm will glow like a glow-in-the-dark toy and better. I have found hornworms with the black light that were so small they were hard to pick off.
How to protect your plants from tomato hornworms
To discourage tomato hornworms, change their environment.
- Practice crop rotation every season. Changing the location of your Tomato crop will help protect it from the hornworms waiting in the soil.
- Decrease the number of locations where worms can lay eggs by removing weeds, dead plants, and plant debris from your garden.
- The most effective way is to remove pick them off plants and destroy them before they can lay eggs.
- To kill them, squash them with your fingers or under your foot, drop them into a basin of soapy water, feed them to your chickens (our favorite way), or go fishing and catch some sunny bank and catch supper.
- One other way of finding a hiding hornworm is to spray your plant with water and gently shake it. This will make the worm wiggle most of the time; if it’s large enough, you will see it.
- You should only water or spray your plants in the early morning before the sun is high. This allows time for the water to slowly evaporate before the sun hits it.
- Spraying or watering your plants when the sun is high will lead to scorching or killing the plant.
- Spraying or watering in the evenings leaves your garden vulnerable to fungus, mold, and mildew.
You can also use this all-natural spray to prevent moths from laying their eggs and to keep worms from feeding on the leaves.
Homemade Garden Spray Recipe
- 1 teaspoon of dish soap
- 1 teaspoon of cayenne pepper
- 2 cups of water.
- Some people also add 1 tsp of garlic oil or powder to this solution.
- Spray the solution over both sides of the leaves.
Remember, you should only spray in the early morning before the sun is high to prevent scorching or killing your plants.
Deter Them With Companion Planting
The sphinx or hawk moth will avoid laying her eggs on your tomatoes if you practice companion planting with a few specific plants. Some excellent choices include:
- Marigolds give off a strong odor that confuses the moth. The best types of marigolds to use are Calendula and the Tagetes.
- Borage helps to deter hornworms. The blooms also attract predatory wasps which help eliminate hornworms naturally.
A trap crop is a crop planted nearby but a safe distance away from the garden to lure pests.
Flowering tobacco plants, which are native to North America, are a wonderful plant to grow near your garden because the Sphynx moth can’t resist them.
You use anything they like as a trap crop, even extra tomato plants you grow from suckers you remove or from extra seeds. I find tomatillos are a good trap crop because they are so large and prolific.
Diatomaceous Earth is a completely natural product composed of tiny fossilized aquatic creatures called diatoms. This helps keep many insects from taking over.
It is like tiny shards of glass to their vulnerable underparts. DE is something we use all over the farm from the garden to the chicken coop, from the barn to the feed for worming.
Make sure you wear a mask and gloves when you are sprinkling it around the garden. You may even want to use goggles. It is very fine dust and may be easily inhaled causing irritation to the lungs, eyes, and respiratory tract. Be sure you are only using food-grade DE around people, plants, and animals!
Natural enemies of the tomato hornworm
Many predators, including lady beetles and green lacewings, target the eggs as well as young caterpillars. The braconid wasp is an important predator that feeds on a variety of caterpillars.
They are considered a parasite of the hornworm. They lay their eggs on the back of the hornworm. As the wasp pupates, it kills the hornworm because they ingest its insides as their food source.
Five Ways to Prevent Hornworms
1. Tilling the Soil
Tilling the soil is one of the most effective methods to keep your tomato plants free from hornworm infestation. As you turn the dirt, any larvae hidden there are killed so they won’t hatch and feed off your plants.
Just make sure you’re not injuring the roots while tilling the earth around your tomato plants.
I personally do not like to till since it can break up soil structure, speed the decomposition and loss of organic matter, increase the risk of erosion, destroy the habitat of beneficial microorganisms, and cause compaction.
2. Crop Rotation
Crop rotation is a very effective technique to keep hornworms under control. There are many good reasons for crop rotation in the garden, hornworm prevention is one of the top ones for me.
3. Natural Insecticides
There are a variety of natural insecticides available in gardening stores. Using natural options avoids any negative effects on the plants or fruits, the soil, and those who consume the produce.
We have used Bio-wash with great results, and it doesn’t add any chemicals to our diet.
You may get rid of the hornworm larvae by covering the ground around the plant with some deep mulch. With 3-6″ of mulch to burrow through they are deterred and often can’t emerge from their holes.
5. Red Garden Trays
We have used these red garden trays with a notable decrease in hornworms. These trays are advertised to “increase tomato yields by 40%”. This is done, they say, by light being reflected off the red tray onto the plant to stimulate growth.
More than any other benefit, I can tell you these trays cut down the hornworm numbers in our garden the year we started to use them by 75% or more.
Tomato hornworms are a common problem for gardeners. They can be controlled by interplanting with certain companion plants, using trap crops, or sprinkling diatomaceous earth around the garden.
Natural enemies of the tomato hornworm include lady beetles, green lacewings, and braconid wasps.
Now that you have learned how to easily spot them, kill them, and prevent them you are equipped to protect your tomatoes and other nightshade plants from being decimated.
As always, we’re here to help!
Read More About Tomatoes