Hungry Caterpillars

I thought that the time for caterpillars this summer was passed and that we were full on butterflies now. I am wrong! I give you Exhibits A and B who are happily munching on my parsley plant:




The day before that I saw one on my fennel and one on the parsley, but I guess either there is a third one roaming around somewhere, or one of them determined that the munching was greener over with his buddy.

I've been searching for a book or poster that contains color photos of caterpillars, and the corresponding butterflies that they become, but alas -- does not seem to exist. So how does one know what become what?