Unveiling the Surprising Dietary Secrets of Swallowtail Butterflies from Caterpillar to Adult

Swallowtail butterflies, belonging to the family Papilionidae, are a captivating group of insects admired for their striking appearance and unique characteristics. These butterflies get their name from their long tail that extends from their hind wings. The tail serves as a diversion, attracting birds’ attention away from their head. With approximately 560 different species worldwide, swallowtails exhibit diverse dietary habits throughout their life cycle. This article delves into the fascinating world of swallowtail butterfly diets, exploring what these creatures eat during their larval (caterpillar) and adult stages.

Swallowtail Caterpillars: Voracious Herbivores

Swallowtail caterpillars are known for their large, thick bodies and can reach up to two inches long before pupating. These larvae undergo five different stages (instars) over the course of 10 to 30 days, during which they feed voraciously to fuel their growth and development. In one day, a hungry swallowtail caterpillar can eat twice its weight in food. This is possible because the caterpillar’s body expands as it eats. As it stretches to the limit, the caterpillar’s exoskeleton splits behind its head, initiating the process of molting. A caterpillar will molt about four to five times, almost doubling in size with each molt.

Host Plant Specificity

Female swallowtail butterflies carefully select host plants before laying their eggs, often flying miles to find the perfect one. In some cases, a female may impersonate other species to help provide protection. One female swallowtail butterfly can lay as many as 1,500 eggs in her lifetime. To protect the eggs from sun, rain, and hungry predators, the female will lay the eggs on the underside of leaves and flowers, or on stems. A fluid released within the eggs helps glue them onto their host plant.

Swallowtail caterpillars are host-specific, meaning they primarily feed on plants from specific families. Some common host plant families include:

Birthwort Family (Aristolochiaceae): The pipevine swallowtail caterpillar, for instance, enjoys eating Virginia snakeroot and vines in the birthwort family.
Citrus Family (Rutaceae): The giant swallowtail caterpillar feeds on herbs and shrubby trees in the citrus family, such as sea torchwood, common hoptree, and wild lime.
Carrot Family (Apiaceae): The food sources, or host plants, for black swallowtail larvae or caterpillars include parsley, dill, and carrot tops.
Custard-Apple Family (Annonaceae): The zebra swallowtail eats shrubs in the custard apple family, along with a variety of pawpaw plants.
Magnolia, Olive, Laurel, and Rose Families: Young caterpillars also consume plants from these families.

Defense Mechanisms

Swallowtail larvae employ various defense mechanisms to protect themselves from predators. Young caterpillars often resemble bird or lizard droppings, providing camouflage. Older larvae have enlarged thoraxes and eye spots that aid in survival. Some swallowtail caterpillars even possess a defensive gland called the osmeterium, located directly behind their heads. When threatened, the caterpillar can shoot out a pair of orange 'horns' from its head and produce a smell like ripe pineapple!

Certain species of swallowtail also protect themselves by being distasteful to predators. As caterpillars, they feed on poisonous plants, so they won’t be an appealing snack to predators.

Specific Examples of Caterpillar Diets

Here are a few examples of swallowtail caterpillar diets based on species:

Pipevine Swallowtail (Battus philenor): These caterpillars primarily feed on plants in the birthwort family (Aristolochiaceae), such as pipevine (Aristolochia spp.). The larvae thrive only on North American species of Aristolochia, dwindling away if raised on exotic Dutchman’s pipes such as Aristolochia elegans. Two twining North American natives - Aristolochia macrophylla and A. tomentosa -make excellent climbers for locations where their wide-ranging roots have room to spread.
Zebra Swallowtail (Eurytides marcellus): Zebra swallowtail larvae consume plants from the custard apple family (Annonaceae), particularly pawpaw trees (Asimina spp.). Females lay pale green eggs on the shoots of young host plants, and the caterpillars eat new growth from the plants along with the flowers.
Giant Swallowtail (Papilio cresphontes): Giant swallowtail caterpillars feed on herbs and shrubby trees in the citrus family (Rutaceae), including sea torchwood, common hoptree, and wild lime. Young caterpillars are brown except for a white and yellowish patch in the middle. They tend to have shiny skin. Sometimes, giant swallowtail caterpillars are called orange dogs.
Black Swallowtail (Papilio polyxenes): The food sources, or host plants, for black swallowtail larvae or caterpillars include parsley, dill, and carrot tops. Female eastern black swallowtail lays her eggs on plants in the parsley family.
Spicebush Swallowtail (Papilio troilus): Spicebush swallowtail larvae feed just on spicebush in late winter and early spring, before the leaves emerge.
Eastern Tiger Swallowtail (Papilio glaucus): Many native and exotic trees and shrubs from the olive, rose, laurel, birch, and magnolia families host the large green caterpillars of tiger swallowtail, which sport two prominent eye-spots. Before pupating, the caterpillars turn from green to brown.

Adult Swallowtails: Nectar Sippers

Once swallowtail caterpillars complete their metamorphosis and emerge as adult butterflies, their dietary habits change drastically. Adult swallowtails primarily feed on nectar from flowers, using their long, straw-like proboscis to reach into deep blossoms and extract this sugary liquid.

Nectar Sources

Adult swallowtails are attracted to a variety of flowering plants, including:

Zinnias
Milkweed
Joe-Pye weed
Butterfly bush (Buddleja spp.)
Phlox
Ironweed
Parsley
Dill
Fennel
Queen Anne’s lace (also called wild carrot)
Citrus

Gardeners tend to have a thing for swallowtail butterflies. Likewise, swallowtails tend to have a thing for certain plants - and certain gardens. Many native and exotic trees and shrubs from the olive, rose, laurel, birch, and magnolia families host the large green caterpillars of tiger swallowtail, which sport two prominent eye-spots.

Other Dietary Needs

In addition to nectar, adult swallowtails also require water and minerals. They obtain these by sipping from moist soil, sand, or even puddles. This behavior, known as "puddling," is particularly common in males, as it helps them acquire essential nutrients for reproduction.

The Black Swallowtail: A Closer Look

The Black Swallowtail butterfly, scientifically known as Papilio polyxenes, is a prominent species in North America. Its geographical range extends from southern Canada through the continental United States to northern Mexico. This butterfly favors open, sunny areas with abundant flora and is commonly found in meadows, fields, gardens, marshes, and even urban settings like parks and backyard gardens.

Black Swallowtail butterflies have evolved several strategies to defend themselves against these predators. Their eggs are small and hidden, caterpillars can absorb toxins from their host plants which make them unpalatable, and the adults are agile fliers.

Attracting Black Swallowtail butterflies involves creating an environment that provides for their needs throughout their lifecycle - from caterpillar to adult.

Black Swallowtail Caterpillar Diet

The preferred host plants are typically members of the Apiaceae family, such as parsley, dill, fennel, and carrot. The food sources, or host plants, for black swallowtail larvae or caterpillars include parsley, dill, and carrot tops.

Read also: Diet of the Butterfly Fish

Black Swallowtail Adult Diet

The adult Black Swallowtail butterflies feed on the nectar of a variety of flowering plants. Plant nectar-rich flowers like zinnias, milkweed, Joe-Pye weed, butterfly bush (Buddleja spp.), phlox, and ironweed. They have long, straw-like proboscises that allow them to reach into deep flowers to access nectar.

Observing Swallowtail Diets

Spotting swallowtail caterpillars requires patience and observational skills. You have to know the right host plants for the species you’re looking for. For most swallowtail species, the caterpillar season occurs between February and November. Usually, female butterflies don’t select the most prominent plants to lay their eggs on.

How can you tell if a caterpillar is nearby? Caterpillar activity includes chewed leaves, nests, silk, and trails. If you can’t find any caterpillars but you see signs of activity, a predator may have gotten to them first. If you want to raise a caterpillar into a butterfly, then one of the best ways to gather caterpillars safely is by laying a white sheet below their host plant. Shake the overhanging branches to dislodge the caterpillars onto the sheet.

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