The Black Swallowtail butterfly (Papilio polyxenes) is a common and beautiful sight in many gardens and fields. Its caterpillar stage, however, is often encountered first, munching away on various plants. Understanding the dietary needs of these caterpillars is crucial for gardeners, butterfly enthusiasts, and anyone interested in the life cycle of this fascinating insect.
Identifying Black Swallowtail Caterpillars
Black Swallowtail caterpillars undergo significant changes in appearance as they grow through five stages of development, known as instars. Young caterpillars are typically black with a white band around their middle, sometimes also displaying reddish-orange spikes. As they mature, the white band may disappear, and they develop green and black bands with yellow spots. Despite variations in coloration, they all develop into healthy butterflies.
Preferred Host Plants
Black Swallowtail caterpillars are relatively picky eaters, primarily feeding on plants in the Apiaceae, or carrot family. Some of their favorite host plants include:
- Parsley: This readily available herb is a popular choice for gardeners and a reliable food source for Black Swallowtail caterpillars.
- Dill: Another common herb, dill is often readily consumed by the caterpillars.
- Fennel: This licorice-flavored plant is another favorite among Black Swallowtail caterpillars.
- Carrots: The tops of carrot plants provide a suitable food source.
- Queen Anne's Lace: Also known as wild carrot, this plant is a common roadside weed that serves as a host plant.
- Rue: This perennial plant is an attractive and reliable host, also favored by Giant Swallowtails.
- Celery: Another member of the carrot family that can serve as a food source.
- Parsnip: This root vegetable's leaves can also be consumed by the caterpillars.
Finding Eggs and Young Caterpillars
Black Swallowtail eggs are small and yellow, typically laid individually on the tops and undersides of the leaves of host plants. Gardeners can bring the eggs inside on the leaves or wait until the caterpillars hatch and grow a little before collecting them. If the eggs are laid on a potted plant, bringing the whole pot inside is an option. For plants in the ground, cuttings can be brought indoors.
Raising Black Swallowtail Caterpillars Indoors
Raising Black Swallowtail butterflies indoors is a fun, easy, and educational activity. They are great to raise indoors for several reasons including abundance, plentiful food source, attractive and interesting caterpillars, and of course beautiful butterflies. To successfully raise these caterpillars, it's important to provide them with a suitable environment and a constant supply of fresh host plants.
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- Caterpillar Homes: Both open and enclosed caterpillar homes can be used. Enclosed environments are often easier to manage, especially as the caterpillars approach pupation and tend to roam.
- Food Supply: Ensure a constant supply of fresh host plants. If using cuttings, place them in water to keep them fresh. Be cautious when using store-bought herbs, as they may contain pesticides. Thoroughly rinse any store-bought vegetation before feeding it to the caterpillars.
- Pesticide Awareness: It’s always best to grow your own host plants if possible to avoid the risk of pesticide contamination, which can be fatal to caterpillars.
Caterpillar Behavior and Development
As the caterpillar grows, it will molt several times, shedding its skin to accommodate its increasing size. During molting, the caterpillar will stop eating and remain still for about 24 hours, becoming delicate and vulnerable. It's important not to disturb them during this process.
Shortly before pupating, the caterpillar will purge undigested food, leaving behind a dime-to-quarter-sized green mess. At this stage, they will also begin to "wander," seeking a suitable location to form their chrysalis.
The Osmeterium: A Unique Defense Mechanism
Black Swallowtail caterpillars possess a unique defense mechanism called an osmeterium. This bright orange, forked gland is located behind the caterpillar's head and emits an unpleasant odor when the caterpillar is disturbed. While harmless to humans, the osmeterium serves to deter potential predators.
Pupation and Emergence
When the caterpillar is ready to pupate, it will attach itself to a stem or stick with silk, forming a chrysalis. The chrysalis can be either green or brown, depending on the surrounding environment. The butterfly will emerge in 1-2 weeks, typically in the morning hours.
After emerging, the butterfly needs to hang upside down to allow its wings to dry and expand. Once its wings are ready, the butterfly can be released outdoors.
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Attracting Black Swallowtails to Your Yard
To attract Black Swallowtail butterflies to your yard, consider planting their favorite host plants and nectar plants. Nectar plants provide food for adult butterflies, while host plants provide food for the caterpillars. Some popular nectar plants for Black Swallowtails include:
- Milkweed
- Phlox
- Red Clover
- Thistle
- Homestead Purple Verbena
- Zinnias
Black Swallowtail Habitat
The Black Swallowtail can be found anywhere East of the Continental Divide in America. The Anise Swallowtail is the Western version of this butterfly and is surprisingly different in appearance considering the caterpillars and chrysalises are nearly identical.
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