It’s not unusual for gardeners to find large caterpillars of the Tobacco Hornworm munching on their tomato or pepper plants. Hornworm caterpillars get their name from the horn-like structure at the back end of the insect and while many species of hornworm caterpillars are known from Wisconsin, the tobacco hornworm is one of the largest and can reach lengths of over 3″. If all goes well, the caterpillars eventually transform into large, grayish sphinx moths with a series of yellowish dots on the sides of the abdomen.
However, tiny parasitic wasps will sometimes kill a caterpillar before it can turn into an adult moth. Female Cotesia wasps inject eggs into a tobacco hornworm caterpillar and the developing wasp larvae live as internal parasites. At a certain point, the wasp larvae have matured and move to the outside of the caterpillar to spin silken cocoons and transform into adult wasps. Biological control in action!