If you are wildly grossed out by insects, you may not want to continue--lots of photos of tomato hornworms ahead.
And this is their handiwork: a totally denuded tomato plant. I had no luck growing tomatoes this year, and this plant has been hanging on but not producing, so I just let them go at it. I figure I've helped the next generation of the Manduca quinquemaculata moth--which these will turn into--thrive. Eat on, dudes!