Pest Control Library: Tomato Hornworm

Found throughout the United States, these large, fat caterpillars feed voraciously on the leaves and fruits of tomatoes, peppers, eggplants, and potatoes. Adults are rather spectacular sphinx moths: grayish-brown with orange spots on the body and a 4- to 5-inch wing span. After overwintering in the soil in 2-inch brown spindle-shaped pupal cases, moths emerge in late spring to early summer to lay greenish-yellow eggs on the undersides of leaves. Caterpillars feed for about a month, then enter the soil to pupate. There is one generation per year in the North; two or more in the South.

Controls

Use Bacillus thuringiensis (Bt) when caterpillars are small. Hand-pick and destroy large caterpillars. Don't worry -- caterpillars cannot sting with their ″horn.″ If you find a caterpillar with what looks like grains of white rice attached to its body, do not remove it. The ″grains″ are the pupae of a parasitic wasp that attacks hornworms. Leave the parasitized caterpillar in the garden so the pupae it carries can turn into more wasps to help control other hornworms.

Photography by Whitney Cranshaw, Colorado State University, Bugwood.org

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