I finally started digging in the mowing edge today, and was working around the tomato plants when I found it: A tobacco hornworm. Tobacco and tomato hornworms eventually become cool-looking hawk and sphinx moths, but at this stage of their lives they will decimate your tomatoes, peppers, tobacco, and eggplants.
My first inclination was to take him over to the driveway and squish him. I wasn't quite sure what was up with the little cottony hangers-on, though, so I decided to come inside and do some internet research to figure out whether this was a normal sight or whether I had yet another pest to deal with in the garden.
I'm glad I did my homework, because the little white things are the cocoons of small braconid wasps, a.k.a. parasitic wasps--in this case, most likely Cotesia Congregata since since hornworms are their favorite hosts. These parasitic wasps lay their eggs inside the skin of a young hornworm larvae. Their babies feed on the insides of the hornworm until they pupate into the cocoons you see above.
Once they emerge from their cocoons the new adult wasps will fly off to find mates and start the parasitization cycle all over again. The hornworms do not survive the raising of these parasitic wasps, so it's best to leave hornworms in the garden if they have cocoons attached. In effect, the hornworm is already doomed and by leaving the cocoons to hatch you will be raising some beneficial insects to help you fight future garden pests.
I don't know what's up with me finding all of these bad bug/good bug combos this week, by the way. But I'm sure getting good use out of one of my favorite books for garden bug identification: Garden Insects of North America by Whitney Cranshaw.
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