Possible second brood in July this year (please enquire) The Black Swallowtail has a wingspan of (8 to 11 centimeters) and is also referred to as the American or Parsnip Swallowtail due to its caterpillars preference for garden plants such as Carrot, Dill, Fennel and Parsnip. Polyxenes has a wide distribution throughout the North American continent where it produces two broods each year. A lovely butterfly that is well worth breeding.