I'm growing caterpillars in my garden. Usually when I see a caterpillar in the garden I go into war mode and get my favorite implement of destruction - a rock. I leave the smooshed caterpillars out for the birds to eat. But when I see caterpillars on my dill, I change tactics. I leave them. "Why" do you ask? Swallowtails love my dill. I wasn't sure that the little larvae I saw three days ago was a swallowtail larva. It looked nothing like it. It was about 1/4" long and its front and back where black and had a white ring around its middle. But I let it live, just in case.
Now in just three days he is an inch long. In the photo, the one at the top is about two days old and the one at the bottom is about three days old. And as you can see, the older one has his true colors (at least I think he won't change too much) . He looks like a black swallowtail.
Right now I have about 10 caterpillars eating my dill and more keep hatching. I'm hoping the birds don't get them. I love the swallowtails flittering around my garden. They are more than worth the price of a little dill.