I just found a medium size Black Swallowtail (BST) caterpillar the other day. It was on a dying Rue Plant, and the foliage was almost gone, so I moved it to one of the two small Rue plants I'm going to plant to replace the dying one. That's one thing about the Black Swallowtail...it can use many different host plants...parsley, Rue, Dill, Fennel, etc. Once a female BST butterfly finds your parsley, it can lay eggs and once they hatch, the cats start eating.
I found a cat on some wild pellitory plants...probably a Red Admiral cat. I've had some outside a while back on the Stinging Nettle, but didn't want to deal with the nettle, so I left them outside. Now, with pellitory...that doesn't sting, so I brought it in to raise.