The tomato hornworm (Manduca quinquemaculata) is a member of the Sphingidae (hawk moth) family. The formal common name is tomato hornworm, but it has been given all kinds of names on the internet including green tomato worm, tomato caterpillar, green caterpillar, and tomato worm moth. Even the adult form has a formal common name, the five-spotted hawk moth.
Tomato hornworms are one of the largest caterpillars you’ll find in your garden and are also one of the most damaging. Understanding their life cycle, which plants they feed on, what their damage looks like, and how to identify them are all important to help you prevent these pests. Here we will cover everything you need to know to keep tomato hornworms away from your veggies.
Five-spotted Hawk Moth Life Cycle
The tomato hornworm life cycle consists of 4 main stages: egg, larva, pupa, and adult. The process begins in mid-spring when adult five-spotted hawk moths emerge from pupating and overwintering in the soil. They begin mating and females begin producing eggs.
Tomato worm eggs are yellow to green in color, about 1.5mm across, and spherical[2]. They are typically laid in clusters on the leaves of host plants, such as tomatoes, and hatch in 4 to 8 days. A single five-spotted hawk moth can lay 1000 to 2000 tomato hornworm eggs in her lifetime.
Larvae emerge from the eggs and begin feeding on plant leaves. They feed on plants in the family Solanaceae which includes vegetables like tomatoes, eggplants, and peppers. Weeds such as horsenettle and nightshade are also solanaceous plants this green caterpillar feeds on. When plants are defoliated, they will feed on the flowers and fruits.
Larvae of this green tomato worm develop through 5 to 6 larval instars over a 3 to 4-week time period[2]. Insect larvae must shed their skin as they grow. The period between shedding is known as an instar. Once the larvae have reached their final instar, they drop to the soil.
The caterpillar will dig down 4 to 6 inches in soil and pupate. Many moths spin a silky cocoon to protect themselves. However, there is no tomato hornworm cocoon since this caterpillar uses the soil for protection instead. After pupating, the tomato hornworm moth emerges and lives for 2 to 3 weeks[2].
Pupae born in mid-spring will emerge as adults in about 2 weeks and produce a second generation. Pupae born during the second, summer generation will overwinter as pupae and emerge as adults the following spring.
Damage Caused By Manduca quinquemaculata
Tomato hornworm damage can be extensive in vegetable crops due to their ability to completely defoliate plants in a few days. Feeding tends to begin at the top of the plant and moves downward as stems are completely defoliated[2]. These big, green caterpillars will also feed on stems and flowers when leaves aren’t available.
Hornworms will also feed on fruits in your garden when leaves become scarce. If you spot tomatoes with worms in your garden, and there’s still plenty of foliage on your plants, you’re likely dealing with the tomato fruitworm (Helicoverpa zea), not the hornworm.
Even if the tomato hornworm caterpillar doesn’t feed on your fruits, their defoliation can lead to fruit issues. Plants need their leaves to turn sunlight into energy for growth. A lack of leaves can lead to reduced fruit production. Defoliation can also lead to sunscalding of fruits due to a lack of shade to protect them[2].
How To Prevent Hornworms In Your Garden
Remove solanaceous weeds from surrounding areas to reduce the number of plants where female moths will lay their eggs. Tilling the soil in your garden at the beginning of the growing season will help to destroy overwintering pupa. By eliminating pupa, you can help decrease the overall adult population which reduces egg laying.
Natural enemies will also help prevent hornworm populations from growing. Braconid wasps can parasitize hornworms, allowing their larvae to eat the caterpillar, ultimately killing it. The wasps will form tiny, white cocoons on the back of hornworms. Hornworms showing signs of being parasitized should be left in the garden to allow the wasp population to continue growing[2].
How To Get Rid Of Hornworms On Vegetables
The best tomato hornworm control is manual removal from plants. Though they easily blend in with foliage when they are small, these tomato caterpillars can be found near their feeding damage. Simply remove them from plants by hand and either squish them or drown them in a bucket of soapy water[1].
Tomato hornworm control can be improved with the use of Bacillus thuringiensis (Bt), a naturally occurring soil bacteria. Bt infects caterpillars when ingested, causing them to stop feeding, which leads to starvation. Bt can be purchased as a spray and is very effective against caterpillars. It washes away easily and must be reapplied to remain effective[1].
Tomato Hornworm vs Tobacco Hornworm
Both tomato and tobacco hornworms are closely related, so it’s no surprise that they look very similar during all 4 life stages. They also feed on the same plants and have overlapping geographical distributions, further complicating identification[2]. The table below describes how to identify them during the egg, larva, and adult stages.
| Life Stage | Tomato hornworm | Tobacco hornworm |
| Egg | Green to yellow, pearly appearance | Greenish color, slightly iridescent |
| Larva | 8 diagonal white stripes along each side, black tail spine | 8 V-shaped marks along sides pointing to their head, orange-red tail spine |
| Adult | 5 orange spots along each side of the abdomen | 6 orange spots along each side of the abdomen |
Frequently Asked Questions
Tomato hornworms are in the insect order Lepidoptera, which includes all butterflies and moths. They are the immature/larval stage of the five-spotted hawk moth. After growing through 5 to 6 larval instar stages, tomato hornworms pupate in the soil for about 3 weeks before emerging as moths.
While tomato hornworms might look dangerous due to their bright coloration and the long horn protruding from their rear end, they are harmless to humans. They cannot sting or bite even when they reach their full size of about 4 inches long.
You should remove tomato hornworms from plants if you don’t want them to eat the foliage. They can consume up to 4 times their weight in foliage or fruit daily. They can quickly defoliate an entire tomato plant before turning into moths.
The most effective way to kill tomato worms naturally is to remove them by hand from plants and drown them in a bucket of soapy water. While they can be hard to spot, since they blend in with leaves, they leave a trail of defoliated stems in their wake. Use this to help you locate them on plants.
The tomato hornworm (Manduca quinquemaculata) and tobacco hornworm (Manduca sexta) are in the same genus and are closely related. There are around 70 species of moth in the genus Manduca, which are known for their large caterpillar size and all species being native to the Americas.
References:
[1] Byron, M. A., & Gillett-Kaufman, J. L. (2018). Tomato Hornworm Manduca quinquemaculata (Haworth)(Insecta: Lepidoptera: Sphingidae): EENY700/IN1206. EDIS, 2018(2).
[2] Volesky, N., & Murray, M. (2019). Tomato Hornworm, Tobacco Hornworm (Manduca quinquemaculata and Manduca sexta). Utah State University Extension ENT-203-18, 1-5.