Hornworms frequently fall prey to nonstinging parasitic wasps that use them as hosts for their young. Tiny braconid wasps, less than 1â„8 inch long, deposit eggs into the caterpillar’s body. The resulting larval wasps feed on the hornworm’s innards until they emerge to spin cocoons and pupate on the outside of the hornworm. If you spot a hornworm with white, ricelike sacs on its back, don't disturb it. The caterpillar has already stopped feeding and will soon die. You can encourage these little beneficial wasps by interplanting tomatoes and other susceptible crops with flowering herbs in the carrot and mint families, such as dill, fennel,* cilantro, basil, sage, oregano, and thyme. Adult parasitic wasps are attracted to their nectar.
Nonparasitized hornworm caterpillars can be controlled by hand-picking and with organic biological pesticides like spinosad and Bacillus thuringiensis (BT).
https://www.organicgardening.com/learn-a ... -hornworms
*Also carrots and parsley, but you need to let some over winter and bloom the next year.
Once you get your eyes trained to spot them, hand picking is easy. Since they rely on camouflage for protection, they hold still.
And do watch for the braconid cocoons - hornworms in my garden usually have them.