I saw a recent posting in the “Raising Butterflies and Moths for Conservation” page on Facebook and a woman who was raising Black Swallowtails had run out of food and bought some “organic”parsley. Unfortunately, all the caterpillars died.
What I’ve learned is that organic produce can be sprayed with certain pesticides which will kill many caterpillars. BT – Bacillus thuringiensis – is a bacterium which is allowed with organic produce. It’s hard to say what was on the parsley, but BT may have been used.
What that now means is that you can’t count on buying food at any grocery store if you plan on feeding it to your caterpillars.
When you are buying new host plants for the garden, instead of buying one plant, buy two or three so that you will have enough host plants when the caterpillars arrive. Obviously, buy plants which don’t have pesticides in the soil.
NPR has a good article on the subject.
Butterfly Gardening 