Swallowtail butterflies, members of the Papilio family, are among the largest and most recognizable butterflies found across many regions. Attracting these striking insects requires a strategic approach that addresses their entire life cycle, not just adult feeding habits. A comprehensive habitat must meet two distinct biological needs: high-energy nectar for flying adults and specific foliage for developing caterpillars (host plants).
Essential Nectar Sources for Adult Swallowtails
Adult swallowtails require a steady supply of nectar to power their strong, gliding flight patterns, which demand significant energy. These butterflies are often drawn to robust, sun-loving flowers that offer a substantial landing platform. Gardeners can plant colorful Coneflowers (Echinacea species), which provide both ample surface area and a high nectar yield throughout the summer months.
Another highly effective nectar source is Zinnia, particularly the flat-topped varieties, which are easy for a butterfly to access with its proboscis. Phlox (Phlox paniculata) and Butterfly Bush (Buddleia) are frequently observed feeding sites, offering clustered blooms. For a native alternative, Joe-Pye Weed (Eutrochium purpureum) and various Milkweed species (Asclepias) also provide rich nectar favored by swallowtails.
The selection should include a variety of flower shapes and bloom times to ensure continuous foraging opportunities from spring through fall. Ironweed (Vernonia) extends the season with late-summer purple blooms, which are particularly attractive to these large butterflies. Providing a dense grouping of these flowers increases their visibility and attraction from a distance, making the garden a more efficient feeding stop.
Critical Host Plants for Larval Development
Unlike the adult stage, the caterpillar stage is highly specialized, relying on specific “host plants” for survival and growth. Female swallowtails will only lay their eggs on plants that the larvae are genetically programmed to consume. The foliage of these plants provides the necessary chemical compounds for the caterpillars to develop and, in some cases, to acquire defensive compounds.
For the common Black Swallowtail (Papilio polyxenes), host plants are generally members of the Apiaceae family, which includes culinary herbs. Parsley, dill, and fennel are reliable choices, and the caterpillars, often called “parsley worms,” will consume the foliage entirely. Queen Anne’s Lace, a common roadside plant, is also readily used by this species.
The Giant Swallowtail (Papilio cresphontes) relies on the Rutaceae family, primarily various citrus trees, earning the caterpillar the nickname “orange dog” in warmer climates. In northern regions where citrus is not native, Giant Swallowtails utilize native alternatives like common rue (Ruta graveolens), prickly ash (Zanthoxylum americanum), or hoptree (Ptelea trifoliata). Expect the leaves of these host plants to be eaten, as this is the intended biological function, and planting extra is advisable.
General Biological Traits of Butterfly-Attracting Flowers
The physical and visual characteristics of a flower dictate its appeal to a foraging swallowtail. Swallowtails possess a long proboscis, which allows them to access nectar from flowers with relatively deep corollas, though they often favor more open structures. They are attracted to flowers that provide a broad, flat surface, serving as secure landing pads for their large wingspan.
The visual system of swallowtails is complex, with some species exhibiting pentachromatic vision, including ultraviolet (UV) light. Studies suggest a general preference for yellow, red, blue, and purple flowers, often with UV patterns that serve as “nectar guides.” Flower scent also plays a role, particularly for females searching for nectar, as olfactory cues can modify their innate color preferences.
Tailoring Your Garden to Common Swallowtail Species
Because the term “swallowtail” encompasses many species, tailoring your garden requires identifying the most likely visitors in your area and planting their specific host plants. The Eastern Tiger Swallowtail (Papilio glaucus) is a widespread species that primarily uses trees and shrubs in the Magnolia and Rose families for its larvae. Effective strategies include planting native wild black cherry (Prunus serotina), tulip tree (Liriodendron tulipifera), or sweet bay magnolia (Magnolia virginiana).
The Spicebush Swallowtail (Papilio troilus) depends on spicebush and sassafras for its larval food source. This species is often found near forest edges, and the presence of these specific shrubs is necessary for its reproductive cycle. Providing large, continuous patches of host and nectar plants is more effective than scattered plantings.
To support successive generations, ensure that nectar sources are available throughout the entire growing season. Grouping flowers with similar bloom times facilitates efficient foraging for the adult butterflies. Additionally, providing a consistently moist, sandy area for “puddling” allows males to absorb essential salts and minerals necessary for reproduction.