There's a kind of dill called mammoth dill. It gets something like 5 feet tall, and as such, is great for swallowtail caterpillars because it has more to eat. I highly suggest planting some. It grows pretty readily from seed. I got a potted one that I thought was fennel, and my goodness was it a surprise when it grew as tall as I am. When it flowers, it can nearly hit 7 feet. Just about every year, we get black swallowtail caterpillars. They grow as big as your finger, and have a snake-tongue-scented stink gland that they can stick out to ward off predators. It's a concentrated dill-smell on the gland, and the cats sure hate it, so I'm guessing it works well. They aren't toxic, just stinky. You'll probably never see the chrysalises, they tend to hide them pretty well. In fact, they also tend to disperse out from the plant to make chrysalises. If you see all your caterpillars abandoning ship when they get big, that's why.