Beginner Gardening: What do I do? , 1 by LOVIE2

LOVIE2 wrote:
I think I killed a black swallowtail caterpillar yesterday and I feel awful about it. In my defense - it scared me 1/2 to death (I'd never seen one before) and it WAS eating my carrot tops. I thought it was a tomato hornworm I keep hearing so much about.
How do you handle this? Do you let them eat until they've cocooned or move them (won't they come back?) or *gasp* kill them? I like butterflies and wouldn't have harmed it if I knew what it was.