The tomato hornworm, the larval stage of the sphinx or hawk moth, is a voracious pest that threatens garden plants, especially tomatoes, peppers, potatoes, and eggplants. Despite growing up to five inches long, this caterpillar is difficult to spot during the day. Its pale green color provides near-perfect camouflage against the foliage, allowing it to inflict extensive damage before a gardener notices its presence.
The Hornworm’s Daytime Hiding Spots
The tomato hornworm is primarily a nocturnal feeder, meaning its daytime activity is focused on concealment and resting. This behavior is a biological adaptation to avoid predators and protect itself from the intense heat of the sun. The larva moves away from the high-visibility, newly grown leaves at the top of the plant where they may have fed during the night.
Hornworms typically hide on the undersides of leaves or along the thicker, interior branches near the main stem of the plant. They choose these spots because the dense foliage offers substantial shade and stability throughout the day. Clinging to the lower, more established parts of the plant minimizes exposure to direct sunlight and reduces the risk of being picked off by birds.
Another common daytime refuge is near the base of the plant, particularly where the foliage is thickest or where there is a layer of mulch or plant debris. Tucking themselves close to the soil line provides protection from the heat and offers a stable anchor point. This strategic positioning allows them to remain close to their primary food source while conserving energy. Their cylindrical bodies and V-shaped white markings further aid in their disguise.
How to Locate Camouflaged Pests
To overcome the hornworm’s camouflage, look for the telltale signs of its presence rather than relying on visual detection of the worm itself. The most reliable daytime indicator is the sight of frass, the caterpillar’s droppings, which are surprisingly large. Frass appears as dark, pellet-like spheres that resemble blackish-green Nerds candy and accumulate directly below where the worm is resting or feeding.
Begin your search by locating these pellets, as they will have dropped from the exact spot the hornworm is currently occupying. Once you find the frass, trace an imaginary vertical line up the plant, and you will usually find the pest clinging to a branch or the underside of a leaf above that point. The older the worm, the larger the frass, making this method more effective as the infestation progresses.
Tracking Plant Damage
Another powerful detection method involves tracking the plant damage, which often appears as stripped branches or large sections of missing foliage. Hornworms usually start feeding at the top of the plant, so search for the most severe defoliation and work your way down the stem to the nearest intact leaves. A hungry hornworm can decimate a significant portion of a plant in a single night, leaving behind bare stems that serve as a clear trail.
When physically inspecting the plant, gently run your hands or fingers along the stems and the undersides of the leaves, starting from the damaged area. Since the hornworm holds on tightly to the plant, this method can help you locate the worm by feel, or sometimes dislodge it entirely. Focusing your search on the lower, denser parts of the plant where they hide during the day significantly increases your chances of finding the camouflaged pest.
Immediate Action: Removing the Hornworm and Preventing Further Damage
Once a hornworm is located, the most direct and effective removal method is hand-picking it off the plant. This approach ensures immediate control without the use of chemical treatments. The worms are entirely harmless, possessing a soft body and no ability to sting or bite, so they can be safely removed by hand, though many gardeners prefer to wear gloves.
The safest way to dispose of the removed pest is to drop it into a container filled with soapy water, which will quickly drown the caterpillar. Alternatively, you can crush the worm, ensuring it cannot return to the plant or pupate in the soil. It is important to check the entire plant thoroughly after finding one, as it is rare for a lone hornworm to be present, and they can hatch in staggered groups.
Recognizing Beneficial Parasites
If you find a hornworm covered with small, white, oval-shaped cocoons resembling grains of rice, you should leave that particular caterpillar in place. These cocoons belong to the larvae of the beneficial Braconid wasp, which is a natural biological control agent. Allowing these wasp larvae to complete their development will help them emerge and target other hornworms, providing a long-term benefit to your garden ecosystem. After removing any worms that are not parasitized, monitor neighboring plants closely and repeat the frass-and-damage search process daily to catch new hatchlings before they grow large enough to cause significant harm.