Answer: Those big green tomato hornworms have a reddish hook on the back end, and generally feed on tomato or tobacco plant leaves. What you might have on your sunflowers is the larvae of a Swallowtail butterfly. They're about the same size and color, but the Swallowtail caterpillar has black spots that appear to be eyes on the head. Or, it could be the larvae of a Luna moth - look for faint yellow-white stripes along both sides of its body. Neither of these caterpillars has the reddish hook that a hornworm has. You can handpick the hornworms and destroy them. You can also hand pick the caterpillars, but rather than destroy them, put them somewhere else in the garden.
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