Tobacco hornworms and tomato hornworms are two closely related caterpillars that look nearly identical at first glance, but a few reliable markings set them apart. The tobacco hornworm (Manduca sexta) has white diagonal lines on its body and a reddish horn on its rear end. The tomato hornworm (Manduca quinquemaculata) has V-shaped markings on its body and a black horn. Both feed on the same plants, cause the same damage, and are managed the same way, so telling them apart is mostly a matter of curiosity rather than strategy.
How to Tell the Caterpillars Apart
Both species are large, bright green caterpillars that can reach 3 to 4 inches long. They blend in remarkably well against tomato foliage, which is why many gardeners spot the damage before they spot the worm. The two key identification features are the body markings and the horn at the tail end.
The tobacco hornworm has white lines running diagonally along each side of its body, angled like forward slashes. Its horn is typically red or reddish-orange. The tomato hornworm’s markings form V-shapes (or chevrons) that point toward the head, and its horn is dark blue to black. If you can get a clear look at the horn color alone, that’s usually enough to make the call.
Despite their names, both species happily eat tomato plants. You’re just as likely to find a “tobacco” hornworm on your tomatoes as a “tomato” hornworm. The common names refer to the plants where each species was first formally described, not to any strong dietary preference.
Differences Between the Adult Moths
The adult forms are large hawk moths that fly at dusk, hovering over flowers to feed on nectar with long, coiled, tube-like mouthparts. In flight, they’re often mistaken for hummingbirds.
The tomato hornworm becomes the five-spotted hawk moth, which has a wingspan up to 5 inches. Its wings are gray and brown, with small hind wings marked by a zigzag pattern. The abdomen is brown and white with a row of five yellow spots along each side.
The tobacco hornworm becomes the Carolina sphinx moth, slightly smaller at up to 4 inches across. Its wings are narrower with a gray, brown, and white pattern, and it carries six yellow spots along each side of the abdomen. Counting those spots (five vs. six) is the most straightforward way to identify the moths, though you’ll need a still or resting moth to do it.
Host Plants and Feeding Damage
Both species feed exclusively on plants in the nightshade family. Tomatoes are the most common target in home gardens, but they’ll also eat eggplant, pepper, potato, and wild nightshade-family weeds like horsenettle and jimsonweed.
Hornworm larvae can devour up to four times their body weight in leaves and fruit each day. A single caterpillar that goes unnoticed for a few days can strip large sections of a tomato plant bare. They primarily eat leaves, but they also chew into green fruit. Damaged fruit often rots on the vine before harvest, or develops dry feeding scars that make it unusable. Because the caterpillars are so well camouflaged, the first sign of a problem is usually large irregular holes in the foliage or dark droppings on lower leaves.
The White Cocoons You Might See
If you find a hornworm covered in small white, rice-shaped projections, leave it alone. Those are cocoons from a tiny parasitic wasp called Cotesia congregata. The female wasp pierces the caterpillar’s skin and deposits her eggs inside, sometimes as many as 65 at once (though the range can be anywhere from 5 to over 160). She simultaneously injects a virus that suppresses the caterpillar’s immune system and prevents it from developing further, keeping it alive as a food source.
The wasp larvae grow inside the caterpillar, feeding on its body fluid, then chew their way out and spin those conspicuous white cocoons on its skin. The caterpillar stops feeding and eventually dies. This wasp targets both hornworm species and is one of the most effective natural controls in the garden. Killing a parasitized hornworm means killing dozens of wasps that would have gone on to parasitize more hornworms, so it’s worth checking before you pick one off.
Managing Hornworms in the Garden
Because both species cause identical damage and respond to the same controls, it doesn’t matter which one you’re dealing with. The simplest approach is handpicking. Regular inspection of your tomato plants, especially the undersides of leaves and along stems, lets you catch caterpillars while they’re still small. Drop them into a bucket of soapy water.
For larger infestations, Bacillus thuringiensis (Bt) is a naturally occurring soil bacterium that kills caterpillars when they ingest it but doesn’t harm beneficial insects, bees, or other wildlife. It works best on younger larvae, so timing matters. Adult moths typically lay eggs on the undersides of tomato leaves in late spring to early summer, and the caterpillars hatch within a few days. Spraying Bt at that stage, when the larvae are small and actively eating new leaf tissue, gives the best results.
Companion planting with basil, marigold, and dill can help attract predatory insects that feed on hornworm eggs and young larvae. Encouraging birds in your garden helps too, since several species will pick hornworms right off the plant. Tilling the soil after harvest can also disrupt pupae overwintering underground, reducing next year’s population.