It seemed to happen so quickly! The tomato hornworm is difficult to see, it's like playing "Where's Waldo" since they are green and just lay along the stems and sometimes hide under leaves. Their damage is easy to detect, the hungry munchers eat all the leaves and just leave the stems. My running partner wanted to see our garden, and instead of a morning run, we spent a half hour searching for these little buggers, we found over 20! The best and most organic thing to do is to keep watch, pick them off, and smash them. I've told the kids that there is a 50 cent bounty on each hornworm brought to me dead or alive.
Beware! check your tomatoes, but they can also infest your potatoes, eggplants, and peppers.
Update: in the comments someone asked what the moth that lays the eggs looks like. Here it is: