Gardeners know: Those colorful swallowtails munching away on your dill, fennel or parsley can eat the entire herb down to a nub in no time at all! Black swallowtails (Papilio polyxenes) enjoy many plants that grow in our vegetable and herb gardens–in fact, they were known as ‘parsley worms’ in the 19th century. But wait–these herbs are introduced species. Why would a native butterfly be attracted to them–and what was it eating before they arrived?
It might seem surprising, but black swallowtails were originally a wet meadow species, feeding on plants such as water parsnip and water hemlock. But as early as the 1820’s, draining and clearing of their habitat began to change the landscape, and the black swallowtail adapted to feed on non-native family members: meadow wildflowers such as Queen Anne’s lace (Daucus carota,) and cultivated garden plants like carrots, dill and fennel. All of these hosts (native or not) are members of the Apiaceae family, with which the swallowtail has co-evolved.
Female butterflies are lured to their host plants by a combination of chemical cues released from the plant, and they have chemoreceptors on their legs to help them find the right spot to lay eggs. (These chemoreceptors are found at the base of spines on the back of the legs, and run up along the spine to its tip.) Females drum their legs against the plant, releasing plant juices; chemoreceptors along the spines tell the butterfly whether she is standing on the correct host plant. And because they are in the same family, plants like dill and fennel “smell right” to swallowtails!
If you’d like to save your herb harvest by offering some native alternatives, golden Alexanders (Zizia aurea), rattlesnake master (Eryngium yuccafolium) and great angelica (Angelica atropupurea) are all fine alternatives for our area.
Or, just plant plenty of parsley!
Photo: Lisa Schneider
