Larvae are pale green with white and black markings (see photo), and undergo 5-6 instars. The first instar is yellow to white in color with no markings. Later instars develop eight white, lateral "V-shaped" marks. A black projection or "horn" on the last abdominal segment gives the caterpillar the name "hornworm."
The caterpillar reaches the final instar in 3-4 weeks, and is 3 1/2 to 4 inches when fully mature. Fully-grown larvae then drop off of the plants and burrow into the soil to pupate. During the summer months, moths will emerge from pupae in about 2 weeks. Moths emerge from the soil, mate, and then begin to deposit the eggs of the next generation on tomato plants.