Large green sphinx moth caterpillars that feed heavily on tomato and related nightshade crops. In hydroponic or greenhouse systems they are usually introduced.
Identification
Larva size: Mature larvae are large, thick-bodied green caterpillars that can become one of the largest pests in tomato crops.
Horn: Hornworms have a distinctive rear horn; tomato hornworms usually have a dark blue to black horn, while tobacco hornworms often have a reddish horn.
Body markings: Tomato hornworms typically show pale V-shaped markings along the sides, helping distinguish them from related caterpillars.
Camouflage: Larvae are well camouflaged on tomato stems and leaf midribs, so damage and frass are often noticed before the caterpillar.
Defoliation: Hornworms chew large amounts of foliage and may strip leaves from branches quickly.
Frass: Large droppings below feeding sites are a strong clue that a hornworm is present above.
Fruit damage: Large larvae may chew shallow or deep holes into tomato fruit as well as leaves.
Lookalikes
Cutworms: Cutworms are usually smaller, duller caterpillars that hide in media and cut seedlings at the base rather than large green defoliators on tomato foliage.
Armyworms: Armyworms can defoliate crops but lack the prominent rear horn and typical hornworm body markings.
Cabbage loopers: Loopers move with an arching looping motion and are generally smaller, without a horn, and more common on brassicas.
Leaf miners: Leaf miners tunnel inside leaves, creating pale mines rather than chewing large missing sections from foliage.
Environmental Triggers
Open greenhouse or outdoor access: Adult moths can enter through open doors, vents, or unscreened areas and lay eggs on tomato plants.
Night moth activity: Adult moths are active around dusk and at night, making evening entry points and lights relevant to monitoring.
Abundant nightshade foliage: Large tomato canopies provide food and shelter for larvae, allowing them to grow unnoticed.
Warm growing temperature: Warm conditions support tomato growth and hornworm larval development.
High sanitation and scouting: Regular leaf inspection, frass cleanup, and removal of larvae prevent major defoliation.
Moth exclusion screening: Screens on greenhouse vents and closed doors reduce adult moth entry and egg laying.
Accessible pupation sites: Loose media, debris, and nearby soil or cracks can allow mature larvae to pupate and persist.
Treatment
Hand removal: Look for large dark frass pellets below tomato branches. Inspect foliage above frass, especially along stems and leaf midribs. Remove caterpillars by hand or with forceps. Dispose of removed larvae away from the grow area. Repeat inspections daily until no new feeding damage appears.
Moth exclusion screening: Install or maintain insect screens on vents, doors, and intake points. Keep doors closed at dusk and night when moths are active. Avoid bright lights that draw moths toward open greenhouse entrances. Inspect screens regularly for gaps, tears, or poor seals.
Egg and early larva scouting: Inspect tomato leaf undersides for single round greenish eggs. Check growing tips and upper leaves for small feeding holes. Remove eggs or small larvae when found. Increase scouting after doors or vents have been open overnight.
Bacillus thuringiensis kurstaki: Use a Bt kurstaki product labeled for edible crops and caterpillar pests. Apply to tomato foliage where young larvae are feeding. Target small larvae before they become large, because older hornworms are harder to control. Repeat according to label directions after new growth, rinsing, or irrigation exposure.
Parasitic wasps and natural enemies: Leave parasitized hornworms with white wasp cocoons in place if crop damage is tolerable, because adult wasps will emerge and attack more hornworms. Avoid broad-spectrum insecticides that kill beneficial wasps. Use natural enemies as part of a broader program with scouting and hand removal. Do not move parasitized larvae into clean production areas.
Remove damaged foliage and frass: Remove heavily damaged leaves if they interfere with scouting or crop hygiene. Clean large frass pellets from trays, media surfaces, and fruit clusters. Use new frass as a clue for remaining larvae. Sanitize hands and tools after handling damaged plant material.
Adult moth monitoring: Monitor adult moth activity near greenhouse entrances or outdoor-adjacent areas. Avoid placing bright attractant traps where they draw moths into the crop area. Use moth activity as a trigger for egg and larval scouting. Combine monitoring with screening and hand removal.
Labeled caterpillar insecticide: Use only products labeled for tomatoes, edible crops, caterpillars or hornworms, and the production environment. Apply when larvae are small and actively feeding. Follow all label rates, restricted-entry intervals, and preharvest intervals. Avoid unapproved products in recirculating hydroponic systems. Combine with scouting and manual removal for best results.
Companion planting is not reliable hornworm control: Do not rely on companion planting as the primary hornworm treatment. Use companion plants only if they do not hide tomato stems or reduce scouting access. Maintain open canopy structure so frass and feeding damage are visible. Combine with screening, hand removal, Bt, and beneficial conservation.
Lifecycle
Egg laying on host leaves: Adult sphinx moths lay single round greenish eggs on tomato or related nightshade leaves, often on leaf undersides.
Egg hatch: Eggs hatch into small larvae that begin feeding on leaves soon after emergence.
Larval feeding and growth: Larvae grow rapidly through several instars, consuming increasing amounts of foliage and sometimes fruit.
Mature larva leaves plant: Full-grown larvae stop feeding and move away from the plant to find a pupation site.
Pupation: Larvae pupate in soil, media, debris, or protected spaces; outdoor populations may overwinter as pupae.
Adult moth emergence: Adult hawkmoths emerge, mate, and can lay eggs on new host plants, restarting the cycle.