So that's what a hornworm looks like. I've never seen one before. Cabbage worms I'm quite familar with from raising broccoli in the past. Strangely enough, I never had much problem with them on the cabbage when I used to grow it.
Zucchinis do seem to grow really fast once they get to a certain size. It's like one day they're not quite big enough, the next day they're huge.