Black swallowtails are easy to attract with dill or parsley. I breed black swallowtails.

thank u. i will look into that. i will try to find them. i will probably plant some dill and/or parsley. is there any other way to attract them? can you buy them?

Grow milkweed and lots of it. Not only will it attract and host the Monarch butterfly which needs everyone's help now, but it will provide nectar for lots of other butterflies, esp Swallowtails. My fave (and the Monarchs') is Swamp Milkweed (Asclepias incarnata) hands-down. It has curb appeal, is well behaved and provides the best food for Monarch cats.
Everlastings (Anaphalis) and Pussytoes, or Cudweed (Antennaria), will attract and host American Ladies.
Nettles will host several butterflies, notably Red Admirals and Commas.
Snapdragons will attract Buckeyes.
And Partridge Pea will attract Sulfurs.
For veggies, you can grow beans, peas, fennel and anything in the Mustard Family (cabbage, radishes,etc).
Round that out c some Zinnias, Mexican Sunflower and Salvias for nectar and you should see results.
Also, Asters, Liatris and Goldenrod provide important nectar waystations for the Monarch Butterfly as it heads South for the Winter.

thanks so much... i will use this.