Yes, several caterpillar species eat tomato plants—and some cause serious damage

Caterpillars are among the most common pests on tomato plants. The ones that damage tomatoes most often are the tomato hornworm, the armyworm, and the cabbage looper. Each species eats different parts of the plant and causes different patterns of damage, so identifying which caterpillar you have tells you how to stop it.

Hornworms are large green caterpillars with white stripes and a horn-like tail. They eat leaves, stems, and fruit, and a single caterpillar can strip a plant bare in days. Armyworms are smaller and darker, moving in groups across plants and eating foliage in ragged patches. Cabbage loopers are pale green and arch their backs as they crawl; they chew holes through leaves and sometimes into fruit. All three are most active in warm weather and can produce multiple generations per season.

Key Takeaways

  • Tomato hornworms are the largest caterpillar pest on tomatoes and can defoliate a plant in a few days if left unchecked.
  • You can hand-pick hornworms and armyworms off plants in the early morning or late evening when they are most visible.
  • Bacillus thuringiensis (Bt) is a natural soil bacterium that kills caterpillars without harming beneficial insects or the tomato plant itself.
  • Netting, row covers, and removing debris where caterpillars pupate reduce pest populations without spraying.
  • Hornworms with white cocoons on their backs should be left alone—parasitic wasps are using them as hosts and will control future hornworm populations.

Identifying tomato hornworms by their damage and appearance

The tomato hornworm is the most destructive caterpillar on tomatoes in most regions. It is a large, fat caterpillar—up to 4 inches long—with a bright green body, white diagonal stripes, and a black horn protruding from its rear end. The caterpillar is straightforward to spot once you know what to look for, but the damage it causes is often noticed first: large, ragged holes in leaves and fruit, sometimes entire branches stripped bare of foliage.

Hornworms feed at night and hide under leaves or in dense foliage during the day. Look for dark droppings (called frass) on leaves below where the caterpillar is feeding—this is often the first sign of an infestation. Hornworms are most active from mid-summer through early fall. A single caterpillar can eat the equivalent of an entire leaf per day, so even one or two on a plant warrant when ready action.

Armyworms and cabbage loopers: smaller but numerous pests

Armyworms are smaller than hornworms—about 1 to 1.5 inches long—and range in color from tan to dark brown or black. They have a distinctive pale stripe running down their back. Unlike hornworms, armyworms move in groups and can appear suddenly in large numbers. They chew ragged holes in leaves and sometimes bore into fruit. Damage from armyworms often looks like the plant was attacked by multiple pests at once, because the caterpillars feed together and move across the plant as a unit.

Cabbage loopers are pale green, about 1.25 inches long, and move by arching their backs—they bring their rear legs forward to meet their front legs, then extend forward again. This looping motion is how they got their name. They chew small, round holes through leaves and can bore into fruit. Loopers are less destructive than hornworms individually, but they reproduce quickly and can build up to large populations by mid-season.

Hand-picking: the fastest way to stop small infestations

If you catch an infestation early—fewer than five caterpillars on the plant—hand-picking is the fastest and most direct solution. Search for caterpillars in the early morning or at dusk, when they are most active and visible. Look under leaves, in the crotches where branches meet the main stem, and inside the densest foliage. Hornworms are easiest to spot because of their size; armyworms and loopers hide more effectively, so search methodically.

Drop caterpillars into a bucket of soapy water or crush them by hand. Wear gloves if you are uncomfortable handling them directly. Check the plant every two to three days for the next week, because new caterpillars may hatch from eggs laid before you removed the adults. Hand-picking works best on smaller plants or when you catch the problem early. On large, heavily infested plants, hand-picking alone will not keep up with the damage.

Bacillus thuringiensis (Bt): a natural caterpillar killer

Bacillus thuringiensis, or Bt, is a soil bacterium that produces a protein toxic to caterpillars but harmless to humans, pets, and beneficial insects. It is sold as a liquid or powder spray under brand names like Thuricide and Dipel. Bt works by disrupting the caterpillar's digestive system; the caterpillar stops eating within hours and dies within one to three days.

Spray Bt directly onto the leaves and fruit, coating both the tops and undersides. explore in the early morning or late evening when caterpillars are feeding and when sunlight is low—Bt breaks down quickly in direct sunlight. Reapply every seven to ten days or after rain. Bt is most effective on young caterpillars; large hornworms may take longer to die. Start spraying as soon as you see the first signs of damage, before populations build up. Follow the label instructions for mixing and process rates.

Netting and row covers to prevent caterpillars from reaching plants

Physical barriers prevent caterpillars from laying eggs on your tomato plants in the first place. Row covers are lightweight fabric sheets that let light and water through but block insects. Drape them over young plants before caterpillars are active in your area, usually in late spring. find the edges to the ground with soil, rocks, or landscape pins so caterpillars cannot crawl underneath.

Remove row covers once the plant flowers and needs pollination from bees, or hand-pollinate the flowers by gently shaking the plant at midday. Fine mesh netting (1/8 inch or smaller) also works but is more labor-intensive to install and remove. Row covers are most practical for small gardens or a few plants. On larger plantings, they become cumbersome. Combine row covers with regular scouting so you catch any caterpillars that do get inside before they cause serious damage.

Removing plant debris and crop rotation to reduce future infestations

Many caterpillar species overwinter as pupae in soil and plant debris. After harvest, remove all dead leaves, fallen fruit, and plant stems from the garden bed. Till the soil to a depth of 6 to 8 inches to expose pupae to cold and predators. In fall, remove tomato cages and stakes and store them away from the garden, as caterpillars sometimes pupate on these structures.

Rotate your tomato planting location each year—do not plant tomatoes in the same bed two years in a row. This breaks the life cycle of pests that overwinter in the soil. Move tomatoes at least 3 feet away from where they grew the previous season. Combine this with removing debris, and you will see fewer caterpillars in the following season. These practices take time but reduce the need for spraying year after year.

What to do if you see white cocoons on a hornworm's back

If you find a hornworm with small white cocoons attached to its back, leave it alone. These cocoons are from a parasitic wasp that lays eggs inside the hornworm. The wasp larvae feed inside the caterpillar, eventually killing it. The cocoons hatch into adult wasps that will hunt and parasitize other hornworms in your garden. By leaving the infested caterpillar in place, you are releasing a natural predator that will control future hornworm populations.

This is one of the few times you should not remove a caterpillar from your plant. The benefit of the wasp population outweighs the damage from that single caterpillar. Mark the plant so you remember not to spray it with Bt or other insecticides, which would kill the wasp larvae inside.

Frequently Asked Questions

Can caterpillars kill a tomato plant?

Hornworms can severely damage or kill young plants by stripping all the leaves, but mature plants usually survive even heavy caterpillar damage. Armyworms and loopers rarely kill a plant outright unless populations are very large. The bigger risk is reduced fruit production from lost foliage.

What time of year are caterpillars worst on tomatoes?

Hornworms and armyworms are most active from mid-summer through early fall, when temperatures are warm. Cabbage loopers can appear earlier in the season and build up populations by mid-summer. Damage is usually worst in August and September in most regions.

Will neem oil kill caterpillars on tomatoes?

Neem oil is less effective on caterpillars than Bt. It works best on soft-bodied insects like aphids and mites. If you use neem oil, spray it directly on caterpillars and repeat every seven days. Bt is a better choice for caterpillar control.

Can I use the same insecticide for all three types of caterpillars?

Yes, Bt works on hornworms, armyworms, and cabbage loopers. Hand-picking and row covers also work on all three species. The main difference is that hornworms are easier to spot and hand-pick because of their size, while armyworms and loopers require more careful searching.

How long does it take Bt to kill caterpillars?

Caterpillars stop feeding within a few hours of eating Bt, but death usually takes one to three days. You may see caterpillars still on the plant for several days after spraying. This is normal—they are dying but have not yet fallen off.