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

Hornworms are the larvae of hawk moths and can grow to 4 inches long. They are bright green with white stripes and a horn-like projection on their rear end. A single hornworm can strip a tomato plant bare in days, so spotting them early matters. You will see dark droppings on leaves below where they feed, or large irregular holes chewed into leaves and fruit. The caterpillars are easiest to find in early morning or late afternoon when they feed most actively.

The fastest way to control a small infestation is to pick them off by hand and drop them into soapy water. For larger infestations or plants you cannot monitor daily, Bacillus thuringiensis (Bt) spray kills hornworms without harming beneficial insects. If you prefer not to spray, you can also plant herbs nearby that attract parasitic wasps—these wasps lay eggs inside hornworms, which kills them from within.

Key Takeaways

  • Hand-picking hornworms works for small numbers and is the fastest method if you check plants every few days.
  • Bacillus thuringiensis (Bt) spray kills hornworms at any size and is safe for humans, pets, and most beneficial insects.
  • Parasitic wasps naturally control hornworm populations if you plant dill, fennel, or cilantro nearby to feed the adult wasps.
  • Dark droppings on leaves and large irregular holes are the first signs of hornworms, so inspect plants weekly during growing season.
  • Hornworms are most active in early morning and late afternoon, making those the best times to search for and remove them.

Hand-picking hornworms from your plants

Hand-picking works best when you catch hornworms early and your plant has only a few. Walk through your garden in early morning or at dusk with a bucket of soapy water. Look for dark droppings on leaves and follow them upward to find the caterpillar. Hornworms blend in with green foliage, so scan the undersides of leaves and around the stem where they hide during the day.

Once you spot a hornworm, pinch it gently and drop it into the soapy water. Do not squeeze hard—you want to kill it quickly, not crush it. If you find a hornworm with white cocoons attached to its back, leave it alone. Those cocoons are parasitic wasp pupae, and the wasp will emerge and hunt other hornworms for you. Repeat your search every two to three days during peak growing season (mid-summer through early fall).

Using Bacillus thuringiensis spray to kill hornworms

Bacillus thuringiensis, or Bt, is a naturally occurring soil bacterium that kills caterpillars but is safe for humans, pets, birds, and most beneficial insects. It works by disrupting the caterpillar's digestive system. Bt spray is sold under brand names like Monterey Garden Insect Spray and Safer Brand Caterpillar Killer. You can find it at garden centers and online retailers.

Spray Bt directly onto leaves, stems, and fruit where you see hornworms or fresh damage. Spray in early morning or late afternoon when hornworms are feeding. Repeat every 7 to 10 days or after rain. Bt works best on smaller caterpillars (under 2 inches), so start spraying as soon as you see the first signs of damage. Larger hornworms take longer to die and may continue eating for a day or two after being sprayed.

Follow the label instructions for mixing and process rate. Bt breaks down quickly in sunlight, so it does not persist in the soil or on plants after a few days. This makes it safe for pollinators and other garden insects that visit your tomatoes.

Encouraging parasitic wasps to control hornworms naturally

Parasitic wasps are tiny insects that lay eggs inside hornworms. When the wasp larvae hatch, they feed inside the caterpillar and kill it from within. You can attract these wasps by planting herbs they feed on as adults. Dill, fennel, and cilantro are the most reliable choices. Plant them near your tomato bed or let some go to flower if they already grow in your garden.

This method takes longer than hand-picking or spraying—it works best as a preventive measure or for managing light infestations over the season. Once wasps establish in your garden, they will hunt hornworms on their own. You may notice hornworms with white cocoons on their backs; these are wasp pupae, and you should leave them alone so the wasps can emerge and continue hunting.

Preventing hornworms before they arrive

Hornworms lay eggs on tomato plants in mid to late summer. You cannot prevent them entirely, but you can reduce the population by removing eggs and early-stage caterpillars. Check the undersides of leaves weekly during growing season. Hornworm eggs are small, round, and light green. Pinch them off and discard them.

At the end of the season, remove all plant debris and till or turn over the soil where tomatoes grew. Hornworm pupae overwinter in the soil, and turning it over exposes them to birds and cold. Do not compost tomato plants that had hornworms; throw them in the trash instead.

When to call in help or try a different approach

If your tomato plants are heavily infested and you cannot keep up with hand-picking, Bt spray is your most reliable option. It is widely available, affordable, and works on plants of any size. If you prefer not to spray anything, accept that you will lose some fruit to hornworms—this is normal even in well-managed gardens.

If Bt does not seem to be working, make sure you are spraying the right parts of the plant (leaves, stems, and fruit where hornworms feed) and reapplying after rain. Also check that you are using a product labeled for caterpillars or hornworms specifically; some insecticides do not work on Bt-resistant strains, though this is rare in home gardens.

Frequently Asked Questions

Can I use neem oil or insecticidal soap on hornworms?

Neem oil and insecticidal soap work on very small caterpillars but are less reliable than Bt on larger hornworms. They also kill beneficial insects more readily than Bt does. Bt is the better choice if you want to avoid harming pollinators and parasitic wasps.

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

Leave it alone. Those cocoons are parasitic wasp pupae. The wasp will emerge in a few days and hunt other hornworms. Removing it kills the wasp and wastes a natural control method.

How long does Bt take to kill a hornworm?

Bt usually kills small hornworms (under 1 inch) within 24 to 48 hours. Larger caterpillars may take 3 to 5 days to die. They stop feeding within hours of ingesting Bt, so damage slows even if the caterpillar is still alive.

Can hornworms come back next year?

Yes. Hornworm pupae overwinter in soil and emerge as moths in late spring or early summer. Tilling the soil at the end of the season, removing plant debris, and not composting infested plants reduces the population but does not eliminate it entirely.

Are hornworms dangerous to humans or pets?

No. Hornworms do not bite, sting, or poison. The "horn" on their rear is harmless. They are safe to handle and to pick off by hand. Bt spray is also safe for humans and pets at label rates.