Hornworms can be very frustrating and difficult to get rid of. They have impressive appetites, which means they can do a lot of damage very quickly – but it is possible to save your plants.
In this complete guide, I’m going to tell you everything you need to know about controlling hornworms organically. You’ll learn about their life cycle, diet, and the damage they cause. Plus discover 5 safe and natural ways to eliminate them from your garden.
I’ll also share my simple prevention tips to help keep hornworms away from your plants so you can avoid them in the future.
What Are Hornworms?
Hornworms are a group of caterpillars from the Sphingidae family, and they eventually turn into large moths.
There are 2 species: the tomato hornworm (Manduca quinquemaculata), and the closely related tobacco hornworm (Manduca sexta).
- Tomato hornworms are present in many parts of North America, along with southern Canada and northern Mexico.
- Tobacco hornworms are more common in the Southern states, and are the species that do the most damage to tomato plants in those areas.
What Do They Look Like?
Both tomato and tobacco hornworms (the larvae) are large caterpillars that can be up to 5 inches long, and have a horn at their rear end, hence their name.
They look very similar – both are green and have white markings on their bodies. But there are two easy ways to tell them apart for a positive ID:
- Tomato hornworms have V-shaped markings on their bodies, and the horn is black.
- Tobacco hornworms have diagonal lines, and their horn is red.
The larvae eventually develop into adult sphinx moths, also called hawk or hummingbird moths. They’re brown or gray with striking patterns, and a wingspan of 4-5 inches.
The eggs are hard to spot, but you can find them on the undersides of the leaves of host plants. They’re smooth, spherical, and pearly white. Once they hatch, the tiny larvae are pale green in color.
Life Cycle
The hornworm life cycle has 4 main stages: eggs, larvae (caterpillar), pupa, and adult moths. The larva is the only stage that feeds on the plants, and the adult moths are actually beneficial pollinators.
Adult females lay their eggs on the undersides of leaves in late spring to early summer, and they usually hatch within a week.
The larvae then begin to feed on the host plant, growing quickly and molting several times. After around 4-6 weeks they reach the pupal stage and create a cocoon in the soil. Depending on environmental conditions, this stage can last anywhere from 2 weeks to a few months.
Finally, the adult moths will emerge and live for around 2 to 3 weeks. In milder climates, this happens in the spring, and there is only one generation per year. In warmer areas, however, there may be multiple generations that overlap throughout the summer months.
What Do Hornworms Eat?
Hornworm caterpillars are voracious eaters, and mainly feed on plants from the nightshade family.
These include tomato and tobacco plants, plus related veggies, like eggplants, peppers, and potatoes. But I’ve also caught them feeding on other plants, like my brugmansias and grapevines.
Despite their common names, tomato hornworms will quite happily feed on tobacco plants, and vice versa.
The larvae primarily eat the foliage of the host plant – often devouring several leaves overnight – but they may also consume the stems, fruit, and flowers.
Where Do They Come From?
Since the adult moths can fly, hornworms can come from anywhere, which makes it very difficult to get rid of them completely.
They are naturally attracted to nightshades. So if you’re growing any of these plants, and there are sphinx moths present in your area, then they will most likely find your garden.
Damage To Plants
Because of their green/brown coloring, hornworms are well-camouflaged and difficult to spot among the foliage they feed on. But there are a few telltale signs of the damage they cause, which you may notice before you see any bugs:
- Chewed or missing leaves from the top of the plant – this is where hornworms like to start feeding. They can defoliate an entire stem or small plant in a very short time.
- The growth of your plant is stunted, or the whole thing is drooping.
- Irregular holes in the fruits where the caterpillars have eaten the flesh.
- The presence of frass (poop or droppings) is another common sign. These are usually large dark green balls.
How To Get Rid Of Hornworms
It’s important to work to get rid of the hornworms as soon as you spot an infestation, otherwise they can quickly cause significant damage to your plants.
Below are some safe and natural treatment methods to try using organic, non-toxic remedies:
Insecticidal Soap
Applying an organic insecticidal soap will help control hornworms, but it needs to come into direct contact with the bugs to kill them.
Spray your plants thoroughly with the solution, either first thing in the morning or late in the afternoon. Be sure to cover the stems, the tops and undersides of the leaves, and any caterpillars or eggs that you see.
Insecticidal soap doesn’t have a residual effect, so I recommend checking your plants regularly for signs of new activity, and reapplying as needed.
Hand Picking
If you don’t have too many plants, getting rid of hornworms by hand-picking them is a simple and effective method.
Don’t worry, they don’t bite or sting – despite that fearsome-looking horn – but you can wear gloves if you don’t want to touch them.
The best times to hand-pick them are early in the morning or late in the evening when they are most active. Gently pull them away from the leaves, then drop them into a bucket filled with a solution of water and mild liquid soap.
Diatomaceous Earth
Diatomaceous earth (DE) is a non-toxic powder made from fossilized algae that kills pests by dehydrating them.
To use it to get rid of hornworms, lightly dust your plants with the powder, focusing especially on the tops and undersides of the leaves, the stems, and around the base of the plant.
Try not to use Diatomaceous Earth too liberally, as it can be harmful to helpful garden insects, too.
Beneficial Nematodes
Beneficial nematodes are microscopic roundworms that feed on the larval and pupal stages of pests.
Follow the instructions on the package to prepare them, then apply them to the soil around the base of the plant.
Learn more about how to use beneficial nematodes to control hornworms and other garden pests.
Bacillus thuringiensis (BT)
Bacillus thuringiensis (BT) is a type of bacteria that occurs naturally in the soil. The caterpillars need to ingest it for it to be effective, so apply it in the late afternoon or early evening when they are more likely to be feeding.
Follow the preparation instructions on the packaging, then spray your plants thoroughly, making sure both the tops and undersides of the leaves are covered.
Related Post: Natural Garden Pest Control Remedies & Recipes
How To Prevent Hornworms
While all the treatment methods above are effective for getting rid of hornworms, the best option of all is to try to keep them from feasting on your plants in the first place. Here are some preventative methods to try:
Encourage Natural Predators
Try planting herbs, like dill, parsley, and fennel, or other flowers around your veggies. They attract insects like lacewings, ladybugs, and parasitic wasps, all of which prey on hornworms.
Create an inviting environment for natural predators by also using insect hotels, or leaving parts of your garden a little wild. Attract birds to your garden too, by installing feeders and birdbaths.
Related Post: How To Release Ladybugs Into Your Garden
Protect Your Plants
Use a lightweight garden fabric or row covers to protect your plants early in the season. This will prevent the adult moths from laying their eggs on the leaves, while still allowing light, water, and air through.
Just be sure to remove the covers when your plant starts to flower, so the pollinators can get to them.
Try Repellent Plants
Companion planting is a good way to protect your crops from hornworms, and involves using flowers or herbs with strong scents to repel the adult moths.
Try planting basil, borage, chives, garlic, or marigolds alongside the ones you want to protect. These all have pungent aromas to deter pests, and can have the advantage of attracting predatory insects as well.
Till Your Soil
Turning and breaking up the soil at the beginning and end of the gardening season is a great way to control hornworms.
It exposes and destroys the pupae that are in the soil, which reduces their numbers for the following season.
FAQs
Hornworms can be bad because the larva feeds on the leaves and sometimes the fruits of plants. These large caterpillars have big appetites, and they can do a lot of damage very quickly. However, the adult moths are harmless to plants, and can actually be beneficial pollinators.
No, a hornworm cannot sting or bite you. Its horn is not venomous and is used as a bluff against predators.
You don’t necessarily have to remove hornworms if they aren’t causing major damage to your plants. But they can decimate a plant very quickly, especially if there are several caterpillars on one plant, so most people choose to remove them.
The tomato hornworm turns into the Five-spotted Hawk Moth, and the tobacco hornworm turns into the Carolina Sphinx Moth. These are large moths that hover when they feed, just like hummingbirds, and are usually most active in the evening and after dark.
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Share your tips for how to get rid of hornworms in the comments section below.
Amy Andrychowicz
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