The eggs of the tomato hornworm are deposited in late spring by adult moths on the underside of leaves. Within five days, hatching beings, and the larva passes through about six stages of development before reaching full growth within four weeks. These larvae burrow into the soil to enter the pupal stage. Adults develop in two to four weeks, and then they make their way to the soil surface.
Once the adults make it to the surface, they begin to mate and lay eggs for the next generation. There are two generations of tomato hornworms each year. Tomato hornworms are found throughout North America. They are some of the most destructive pests known, not just for tomatoes, but also for pepper, tobacco, potato and eggplant. Tomato hornworms are some of the largest caterpillars seen in common gardens, and the adults are large moths with a wingspan around 5 inches. These moths are referred to as sphinx, hawk or hummingbird moths.
While tomato hornworms are large, they can be difficult to spot because of their protective green coloring that acts to camouflage them. As these hornworms continue to grow in their caterpillar stage, they do increasingly more damage. It is estimated that in the adult caterpillar stage, there is more defoliation done by the hornworm than in all of the earlier stages combined.