Hornworms are large green caterpillars that eat tomato leaves and fruit, and you can remove them by hand, spray them with insecticide, or use natural predators

Hornworms are the caterpillar stage of the hawk moth. They are fat, green, and can grow to 4 inches long. A single hornworm can strip a tomato plant bare in days because they eat constantly. The good news: they are visible, slow-moving, and you have several ways to stop them before they destroy your crop.

The fastest method is hand-picking. Walk your plants in early morning or late afternoon when hornworms feed most actively. Look for dark droppings on leaves (a sign a hornworm is above), then scan the plant top to bottom. Pinch or snip the caterpillar off and drop it into soapy water. One plant can have only one or two hornworms, so this takes 10 minutes.

If you find many hornworms or prefer not to handle them, spray the plant with Bacillus thuringiensis (Bt), a naturally occurring soil bacterium that kills caterpillars but is safe for humans, pets, and beneficial insects. Products like Monterey Garden Insect Spray contain Bt. Spray in the evening, coat both sides of leaves, and repeat every 7 to 10 days if new hornworms appear. Bt works only on young caterpillars—once they reach full size, it is less effective.

Key Takeaways

  • Hand-picking hornworms in early morning or late afternoon is the fastest and cheapest method, and one plant usually has only one or two.
  • Bacillus thuringiensis (Bt) spray kills young caterpillars and is safe for people and pets, but works best on small hornworms.
  • Neem oil suffocates eggs and soft-bodied insects but requires repeated applications and works best as prevention before hornworms arrive.
  • Parasitic wasps lay eggs inside hornworms, killing them from within; you can buy them online or attract them by planting flowering herbs nearby.
  • Check plants twice a week during summer because hornworms grow fast and can cause serious damage in a few days.

Hand-picking: the simplest method

Hand-picking works because hornworms are large, immobile, and usually solitary. A tomato plant rarely hosts more than two at once. Search the plant systematically: start at the top and work down, checking both sides of every leaf and the stem. Look for chewed leaves with ragged edges and dark droppings (frass) on leaves below—the droppings are often the first sign.

Once you spot a hornworm, pinch it between your fingers or use pruning shears to cut it off. Drop it into a bucket of soapy water to kill it quickly. Wear gloves if you are squeamish; the caterpillar is harmless but will thrash. Some gardeners throw them into a compost bin or bury them in soil, where they decompose and feed the garden.

Do this check twice a week during summer, especially in July and August when hornworms are most active. Catching them small (under 2 inches) prevents major leaf loss. If you find a hornworm with white cocoons attached to its back, leave it alone—parasitic wasps have already laid eggs inside it, and it will die naturally while feeding the next generation of wasps.

Bacillus thuringiensis spray for larger infestations

Bt is a soil bacterium that produces a protein toxic only to caterpillars. When a hornworm eats a leaf coated with Bt, the protein damages its gut and it stops feeding within hours, then dies within 2 to 3 days. Bt does not harm humans, pets, earthworms, or beneficial insects like bees and ladybugs.

Buy Bt products at garden centers or online under names like Monterey Garden Insect Spray, Safer Brand BioWorm, or Bonide Thuricide. Mix according to the label, spray in the evening (when hornworms feed and Bt is less likely to break down in sunlight), and coat both the top and underside of leaves thoroughly. Repeat every 7 to 10 days if new hornworms appear. Bt works best on caterpillars under 1 inch long; older, larger hornworms have tougher guts and may survive the spray.

Bt breaks down in sunlight within 3 to 5 days, so rain or overhead watering does not reduce its effectiveness—only time does. It is safe to harvest tomatoes when ready after spraying.

Neem oil as a preventive treatment

Neem oil is pressed from the seeds of the neem tree and works by coating insects and their eggs, suffocating them. It is less effective on large hornworms than on eggs and young caterpillars, so use it as a preventive spray starting in late spring, before hornworms hatch.

Mix neem oil concentrate according to the label (usually 1 to 2 tablespoons per gallon of water) and spray in the evening when bees are not active. Coat both sides of leaves and the stem. Repeat every 7 to 10 days throughout the growing season. Neem oil can damage tender new growth if applied in hot weather above 85°F, so spray in early morning or late evening and avoid the hottest part of summer.

Neem oil is safe for humans and pets but can harm some beneficial insects if sprayed directly on them. It is slower-acting than Bt—insects may take several days to die—but it also kills spider mites, aphids, and whiteflies, making it useful for general pest control.

Parasitic wasps: natural predators that work over time

Parasitic wasps are tiny insects (smaller than a grain of rice) that lay eggs inside hornworms. The wasp larvae eat the caterpillar from the inside, killing it. The wasps do not sting humans and are completely harmless to people and pets.

You can buy parasitic wasps online from garden suppliers and release them in your garden. They cost $20 to $40 per shipment and come as pupae on a card. Hang the card near your tomato plants and the wasps will emerge over a week or two, then hunt for hornworms. Once released, they establish themselves and return year after year if you do not use broad-spectrum insecticides.

You can also attract native parasitic wasps by planting small-flowered herbs like dill, fennel, cilantro, and yarrow near your tomatoes. Wasps need nectar and pollen to survive, and these plants provide both. This method is slower—it takes weeks for wasps to find your garden—but costs nothing and builds a permanent pest-control population.

Preventing hornworms before they arrive

Hornworms hatch from eggs laid by hawk moths in late spring and early summer. The moths are attracted to tomato plants at night. You cannot prevent the moths from visiting, but you can reduce egg survival and catch caterpillars early.

Inspect plants twice weekly starting in June. Remove any eggs you find—they are small, round, and usually on the underside of leaves—and crush them. Keep the area around tomatoes clear of weeds and debris where pupae overwinter. In fall, after harvest, dig up the top 4 inches of soil around the plant base to expose pupae to birds and cold.

Avoid broad-spectrum insecticides like carbaryl or permethrin, which kill beneficial insects and parasitic wasps. If you must spray, use Bt or neem oil instead, which target only caterpillars and soft-bodied insects.

When to call a professional

You do not need professional help for hornworms. They are straightforward to manage with hand-picking or Bt spray, and a home gardener can handle an infestation in an afternoon. If your entire garden is infested with multiple pests and you do not have time to scout and spray, a local pest control service can help, but it is rarely necessary for hornworms alone.

If you are unsure whether the caterpillar on your plant is a hornworm, take a photo and contact your local cooperative extension office. They can identify it and recommend the best control method for your region.

Frequently Asked Questions

Can I use regular insecticide like malathion or carbaryl on hornworms?

You can, but it is not the best choice. These broad-spectrum insecticides kill hornworms but also kill parasitic wasps, ladybugs, and bees. Bt and neem oil are safer for beneficial insects and work just as well on caterpillars.

What if I find a hornworm with white cocoons on its back?

Leave it alone. Parasitic wasps have already laid eggs inside it. The caterpillar will die in a few days, and the wasps will emerge to hunt other hornworms. This is free pest control happening on its own.

How many hornworms can one tomato plant have at once?

Usually one or two. Hornworms are solitary and territorial, so you rarely find more than two on a single plant. If you find one, check the rest of the plant carefully—there may be a second hiding on a lower branch.

Can I spray Bt if it rained yesterday?

Yes. Bt breaks down in sunlight, not water. Rain does not wash it off or reduce its effectiveness. Spray whenever you see hornworms, rain or shine.

Do hornworms come back every year?

Yes. Hornworm pupae overwinter in the soil and emerge as moths in late spring. If you grow tomatoes in the same spot year after year, you will see hornworms every summer. Rotating your tomato bed to a different location each year reduces the population.