NO! Not even if the herbs or vegetables are guaranteed organic!
Non-organic fresh herbs and vegetables are coated with chemicals that will kill your caterpillars. But even certified organic foodstuffs are often coated with Bacillus thuringiensis (Bt). Bt is a bacteria that occurs naturally in soil and so is considered “organic.” It doesn’t hurt people, but it does kill insects (which is why “organic” famers use it). The symptoms of Bt poisoning are that your caterpillars take a few bites and then cease eating, forever. They die of starvation about three days later.
Your caterpillars have to feed on herbs or plants that you can be sure have not been treated with anything. That means food you’ve grown yourself, or that came from a nursery or farmer that you trust did not use any chemicals, including Bt.
Remember Black Swallowtails can eat any of dill, fennel, and parsley, and they can be switched from one to another if necessary. Great Southern Whites can eat almost any cabbage or kale, as well as nasturium (the entire nasturium plant can also be eaten by humans — the flowers are great on salads!).
See the related FAQ, I’m running out of host plants; can I buy more host plants from my local nursery?
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