Sparing the Tomato Hornworm

Sparing the Tomato Hornworm was originally published in the BFEC Newsletter, Vol. 17/No. 3, Summer 2013. 

Much reviled by gardeners, the tomato hornworm is a caterpillar that loves
(you guessed it) tomatoes. In true “very hungry caterpillar” style, the tomato hornworm and its cousin the tobacco hornworm leave gardeners dumbfounded when they discover yesterday’s healthy tomato, potato or pepper plant stripped of its foliage.

If your fist instinct would be to destroy the bug, consider that this mammoth caterpillar turns into a magnificent sphinx moth with a four-inch wingspan. It uses its impressively long, straw-like mouth (called a “proboscis”) to drink nectar while hovering over night-blooming plants.

The moth lays eggs on plants in the nightshade family, which have round or star-shaped flowers. This does include your tomato plants, but also wild species like the jimsonweed above. If you decide to spare a tomato hornworm’s life, simply move it to a spot far, far away from your garden, preferably with other nightshade plants available.

Fun Facts

• The hornworm caterpillar gets its name from the “horn” found on its rear end. Though it looks potentially painful, the horn cannot sting curious humans.
• The sphinx moth owes its name to the hornworm’s defense posture. It raises the upper third of its body and tucks its head in a stately, sphinx-like position. The hornworm pictured here is striking this pose, even while hanging upside down.
• Tomato and tobacco hornworms spend their winter underground. Sensitive to the change in daylight that comes with fall, they burrow in loose soil to form a chrysalis, where they will remain until emerging as a moth in late spring.
• Hornworms are not without natural enemies. If you find one covered with tiny white sacks, you have discovered the cocoons of parasitic wasp laravae. The larvae will devour the caterpillar as they develop.