Carrot tops and rue.

Martha

Their foods will belong to the Apiaceae family. Add cilantro to the list of things that they eat.....none of the plants listed by you, Annie, are suitable.

Mock bishop's weed/Ptilimnium capillaceum is a weed native to my area. It grows in wet spots. It came up on its own in parts of my former garden, and periodically I'd find black swallowtail caterpillars on it. It looks like dill and fennel. There may be some wild member of the Apiaceae/carrot family that grows in your area that you can use.

Sherry

In addition to the above mentioned plants, I've also read that the BST will eat cow parsnips, Golden Alexander, and Queen Anne's lace. At my place the BST butterflies lay their eggs on the rue, fennel, and parsley. One year when I planted carrots, a couple laid on those, but it didn't seem to be their favorite plants. We didn't get many BSTs this year. They haven't laid on the parsley at all this year. It seems like here their favorite plant to lay on is the rue, but it makes me itchy so my daughter has been taking the BST eggs/cats and GST eggs/cats off of the rue and also picking it to feed them. It's the easiest thing to feed them and holds up the best out of the things that I have for them. The rue plants have more substantial leaves than the parsley or fennel and the rue lasts longer in water for me.

If you don't have luck finding anything to feed them, you can feet them organic parsley. You have to test it by putting one caterpillar on it. If it's been treated with Bt (an organic bacteria that will kill caterpillars), the caterpillar will stop eating within 12 hours and die. It's sad, but better to sacrifice one than all of them.

In the thread linked below, I show the organic brand I'm using now. I have about 80 (not a typo!) caterpillars and eggs and not enough rue in my garden to feed them all. Mine don't mind switching food at all. They might go on a hunger strike for a few hours, but will eat it :)

[Thread with notes about organic parsley[(https://www.houzz.com/discussions/another-population-explosion-dsvw-vd~5456051?n=10)