Encyclopedia Article

Description of hornworms

The short, slender horn on the tip of the abdomen is red on the tobacco hornworm and green on the tomato hornworm.  Both species have diagonal white stripes along the sides of the body.

Life cycle of hornworms

The insect spends the winter in the soil as a large, brown pupa.  The adult hawk moths emerge in mid- to late June and lay eggs on the lower side of host plant leaves.  The larvae feed on the foliage for 4 to 5 weeks before growing to the commonly–seen size of 3 to 4 inches long.

Damage caused by hornworms

The well–known tomato hornworm is more often a curiosity in gardens rather than a pest, though outbreaks have been known to occur.  A hornworm can eat a considerable amount of foliage that may look like severe damage, but actual yield loss is probably slight.

Ravenous leaf feeding by hornworm larvae may result in extensive defoliation.  Hornworms blend in with the foliage and are difficult to see until much defoliation has occurred.

Management of hornworms

Parasitism and other natural factors keep hornworm populations sufficiently low in most gardens.  Carefully watch for larvae and feeding from June to harvest.  When hornworms are observed, handpicking is usually sufficient control action.  Spraying is seldom warranted.

Do you live in Iowa and have an insect you would like identified?

The Iowa State University Plant & Insect Diagnostic Clinic will identify your insect, provide information on what it eats, life cycle, and if it is a pest the best ways to manage them.  Please see our website for current forms, fees, and instructions on preserving and mailing insects.   

Contact information for each states diagnostic laboratory for U.S. residents.  If you live outside of Iowa please do not submit a sample without contacting the Plant & Insect Diagnostic Clinic.