Black Swallowtail Diet: Parsley, Dill, and Nectar
Black swallowtail caterpillars eat leaves, flowers, and seeds of plants in the parsley family, including parsley, dill, fennel, carrot, celery, and Queen Anne’s lace. Adult black swallowtails do not eat those leaves; they drink nectar from flowers and use different plants for their own energy. Planting both host herbs and nectar flowers supports the full life cycle.
What Do Black Swallowtail Caterpillars Eat?
Black swallowtail larvae are specialists on parsley-family plants. University of Minnesota lists parsley, carrots, dill, fennel, celery, and Queen Anne’s lace among their hosts. They may prefer flowers and seeds when available, but leaves are also important food.
A caterpillar on a parsley plant is often called a parsley worm. The name is useful because it links the insect to its host, not because it is a worm. It is the larval stage of Papilio polyxenes, the black swallowtail butterfly.
Why Do Caterpillars Like Parsley and Dill?
Female butterflies choose these plants because the caterpillars are adapted to feed on their chemistry. Many insect larvae cannot safely use the same leaves. Black swallowtail caterpillars can, which gives them a reliable food group across gardens, roadsides, and fields.
Dill, parsley, fennel, and carrot are convenient human food plants, so gardeners notice the caterpillars quickly. Plant an extra row or container if you want to share. One small herb plant can be stripped by several large larvae, but established herbs often regrow when cared for well.
What Do Adult Black Swallowtails Eat?
Adults feed primarily on flower nectar. They visit blooms for sugars and water rather than chewing leaves. A garden with flowers across the season gives adults more chances to refuel, find mates, and lay eggs on nearby host plants.
Penn State recommends a mix of nectar plants and clusters of flowers, because groups are easier for butterflies to find than isolated blooms. Choose plants suited to local conditions and try to have something flowering from spring through fall rather than relying on one short bloom period.
What Nectar Plants Work Well?
Common butterfly nectar plants include coneflowers, asters, bee balm, butterfly weed, verbena, Joe-Pye weed, sedum, and many mint-family flowers. The best choices depend on region, light, soil, and bloom season. Native plants can be especially useful because they fit local insects and climate.
Look for open flower forms with accessible nectar. University of Minnesota cautions that double flowers are often bred for appearance rather than nectar. A mix of flower shapes and colors is better than betting the garden on one named butterfly plant.
Do You Have to Sacrifice Your Herbs?
No, but share deliberately. If parsley is for the kitchen, grow several plants and designate one for caterpillars. Move a caterpillar only to another healthy plant in the same host family nearby. Do not place it on a random leaf; it may starve even if the plant looks green and edible to you.
Illinois Extension notes that parsley can support both harvest and caterpillars with little overlap when plants are grown well. The practical compromise is simple: grow enough, harvest selectively, and enjoy finding the larvae as a sign that the garden has become habitat.
When Do Black Swallowtails Feed?
Caterpillars feed through the warm growing season. In Minnesota, black swallowtail adults may emerge in late spring and again in summer, with caterpillars present into September. Timing changes across the species’ wide range, so the same herb can host larvae at different dates in different places.
Adults emerge when flowers are available and may look for host plants soon after mating. The plants are connected in time: herbs support larvae, nectar supports adults, and a protected place supports the pupa through the next transition.
Should You Spray Caterpillar Hosts?
Avoid pesticide sprays on plants where you want swallowtails to develop. Even a product aimed at caterpillars does not distinguish a crop pest from a black swallowtail larva. Direct contact with soaps and oils can also kill or injure caterpillars.
If an edible herb needs protection, use physical measures or harvest parts of the plant while leaving a separate host plant for larvae. Identification comes before treatment. The green-and-black striped caterpillar on dill is usually a visitor worth keeping.
What Is the Simple Answer?
Black swallowtail caterpillars eat parsley-family plants such as parsley, dill, fennel, and carrot. Adult butterflies drink nectar from a range of flowers. Grow both kinds of plant if you want to support them through every stage.
For the broad diet of the whole swallowtail group, see what swallowtail butterflies eat. Leaf-chewing and nectar sipping belong to different life stages.
