source: Grow Veg
Tomato hornworms are green caterpillars the exact shade of tomato leaves, with white diagonal stripes on their sides and a fleshy pointed tip at their tails. When tomato leaves are mysteriously missing, following trails of pebbly, dark green excrement will lead you to the hornworms. Young hornworms are tiny green caterpillars, but they gradually grow to 4 inches (10 cm) long. Tomato hornworms are the larvae of a mottled brown hawk moth that flies at night.
Tomato hornworms weaken plants by removing foliage, and in some cases they chew holes in fruits. The adult moths typically lay several eggs on a plant, and the combined feeding by multiple hornworms can remove so much foliage that the fruits become susceptible to sunscald.
Tomato hornworms overwinter as pupae in the soil near tomato plants, and fall cultivation will kill most of them. Yet moths can easily fly into the garden from other areas, so check plants often for missing leaves starting in early summer.
Gather hornworms by hand and dispose of them in the compost. Once they are removed from their host plants, hornworms quickly die. Hornworms cannot bite or sting. In severe cases, application of a Bt-based biological insecticide will quickly bring hornworms under control.
If you encounter a tomato hornworm with elongated white cocoons attached to its body, these are evidence of braconid wasps – tiny beneficial insects that lay their eggs on hornworms.
There is no magic bullet for keeping your garden pest-free. It involves a lot of work and diligence on your part.
These green caterpillars will show white spikes protruding from their bodies. If you are a gardener, and if you ever spot a hornworm sporting these white spikes, then you should not kill them, but instead let them die on their own. These white protrusions are actually parasites. To be more clear, these parasites are braconid wasp larvae. The wasp adults will plant their eggs within the bodies of these hornworms. The resulting larvae will then slowly feed on the innards of the caterpillar. These infected hornworms, if spotted, should be left alone so that gardeners can take advantage to the benefits of the parasite. Once the hornworms become adults, they will not only destroy the infected hornworm, but they will fly around a garden destroying every other hornworm in sight. The wasps begin this killing spree immediately upon leaving their cocoons.