Tomato worms, also called tomato hornworms, are a type of caterpillar that feed primarily on plants in the nightshade family, such as tomatoes and eggplants. They are relatively large caterpillars, measuring around 4 inches (about 10 centimeters) in length when fully grown. The pests can be difficult to see on a tomato plant, because they have a color and texture similar to the stems of the plant, although the body of the tomato worm does have angular white stripes on the side. Signs that tomato worms are attacking a tomato plant include large areas of leaves, stems and fruit that have been eaten, as well as small black droppings either on the underside of leaves or on the leaves near the bottom of the plant. When tomato worms are done feeding on a plant, they drop into the soil to finish growing into a moth and can overwinter in the soil if not interrupted, emerging in the spring to lay more eggs.
In most gardens, tomato worms are fairly easy to identify. They are a large species of caterpillars and are light green in color, almost identical to the color of the stems of traditional tomato plants. Along the sides of the caterpillar are white arrow-shaped markings that point toward the head. On the rear of the caterpillar there is a small, dark — almost black — spike that looks like a horn. A similar type of caterpillar, called a tobacco worm, has an almost identical appearance except the horn is red and the white markings on the side do not make chevron or arrow shapes and instead are just angled white slash marks.
The primary evidence that tomato worms have infested a tomato plant is areas of the plant where large parts of leaves have been eaten away. The caterpillars also will eat the stems of the plants and the fruit when it is small and can be easily managed. As the worms move through the plant, they tend to hang upside down, which means they occasionally will leave dark droppings on the underside of the leaves or, if the droppings fall off, they will culminate on the surface of the lower leaves of the plant.
One thing to note is that some tomato worms might appear to have small white eggs attached to their exterior. These eggs are the larvae of a type of wasp that lays its eggs in a tomato worm. In general, worms that have the wasp larvae are left alone to produce more wasps that will, in time, help to control the population of tomato worms. The most immediate method, however, of handling a tomato worm infestation is to physically remove the worms and dispose of them. If the tomato worms return year after year, then the larvae might be pupating in the soil, meaning the soil should be aggressively tilled to destroy them to a depth of roughly 6 inches (about 15 centimeters).