Identifying Hornworms on Portulaca: Tomato or Tobacco Hornworm?

Large Green Caterpillar with a Horn: What Is It?

A gardener in the Santa Cruz Mountains found a bright green caterpillar over 2 inches long, with yellow markings and a prominent yellow horn on its rear, feeding on portulaca. This description matches either the tomato hornworm (Manduca quinquemaculata) or tobacco hornworm (Manduca sexta).

Key Differences

• Tomato hornworm: Eight V-shaped white marks; black horn.
• Tobacco hornworm: Seven diagonal white lines; red horn.

Both are larvae of sphinx moths and voracious feeders on nightshade family plants (tomato, pepper, eggplant, tobacco) but will occasionally eat other plants like portulaca.

Immediate Action Required

These caterpillars can defoliate a potted plant in days. Hand-pick and destroy them—drop into soapy water or snip with scissors. Check the plant daily for more.

Organic Control Options

• Bacillus thuringiensis (Bt): A microbial insecticide specific to caterpillars. Safe for beneficials.
• Beneficial insects: Braconid wasps parasitize hornworms. If you see white cocoons on a caterpillar, leave it—the wasps will emerge and control others.

Prevention

• Till soil in fall to disrupt pupae.
• Rotate nightshade crops.
• Use row covers early in the season.