What Kind of Worm Eats Leaves Off of Tomato Plants?

Identification

• Tomato hornworm bodies are the same green as the tomato plant, making them difficult to see despite their size, which can be up to 4 inches in length. Eight white, diagonal stripes segment the body and a bluish-black "horn" or stinger-like projection protrudes from the caterpillar's last abdominal segment. The horn is actually only a disguise to discourage predators, but it is harmless. A related caterpillar, the tobacco hornworm (Manduca sexta), has seven white stripes, a red to black horn and is slightly smaller than a tomato hornworm, but it shares an identical appetite.

Life Cycle

• A sphinx moth, also known as hummingbird or hawk moths, can have a wingspan of up to 5 inches. A large proboscis sips nectar from flower blossoms. In late spring, adult females lay their eggs on the tops and undersides of tomato plant leaves. Six to eight days later, the eggs hatch and white to yellowish larvae emerge. The white lateral markings and horn appear later, as the larvae grow. After three to four weeks, the larvae are fully mature and drop to the ground to burrow and pupate.

Plant Damage

• Hornworms eat heartily on tomato plant leaves. By the final stage of its larval development, the caterpillar consumes over 90 percent more food than it had in all its previous stages combined. Since the worm is so well camouflaged, it is often difficult to detect until leaf damage has already occurred. The larvae are sensitive to sunlight and remain on the undersides of leaves during the day. At dawn and dusk, the larvae move further out on the plant to feed and are more easily detectable. Large black droppings, called frass, on the ground below plants are another sign of an attack.

Control

• The best defense is to pick the worms off plants and destroy them as soon as they are discovered. After the larvae fall to the ground and enter the pupate stage, tilling the soil beneath tomato plants can also be effective in exterminating these garden pests.

Other Leaf Eaters

• While tomato and tobacco hornworms are the most likely cause of leaf damage to tomato plants, a few other worms also cause damage. Cabbage loopers are green with longitudinal white stripes and are just over an inch in length. They prefer only the tender parts of tomato plant leaves and avoid eating the veins. Tomato fruitworms range in color from pale yellow to red, green or brown. These are the same worms often found in fresh corn. They only eat foliage early in their development and quickly turn to the fruit itself.