Black Swallowtail Guide
Quick Facts
A Black Swallowtail caterpillar eating fennel
Name: Eastern Black Swallowtail (Papilio polyxenes asterius)
Size: 2.5 - 4.3 inch wingspan (6.4 - 10.9 cm) (males and females similar in size)
Host plants: Plants in the Apiaceae family including:
Non-Native: parsley, dill, fennel, carrots, and Queen Anne's lace
Native: Alexanders, Angelica, Wild Licorice, and Canadian Hornwort
Adult Diet: Nectar from native wildflowers such as milkweed, coneflower, black-eyed susans
Caterpillar stages: 5 instars (final instar bright green with black bands and yellow spots)
Defense: Osmeterium (an orange, forked gland) releases a foul-smelling substance to deter predators; camouflage and warning coloration
Range: Eastern and central U.S., parts of Canada, and south into Central America Habitat: Open fields, gardens, meadows, and areas near their host plants
Chrysalis colors: Green or brown, influenced by the surroundings
Number of flights: 2-3 flights per year (spring through early fall)
Conservation status: Not currently listed as threatened or endangered
Rarity: Common in its range and a familiar sight in gardens and meadows
How to Help:Plant a patch of host plants - such as fennel or dill - on your property, or try native Golden Alexanders (Zizia aurea).
Black Swallowtails
Adult Black Swallowtail Butterfly
Overview
The Eastern Black Swallowtail (Papilio polyxenes asterius) is one of the most recognizable and widespread butterflies in its range. Known for its striking black wings adorned with yellow spots and blue highlights, this butterfly is a favorite among gardeners and nature enthusiasts. Its adaptability to human-altered landscapes and non-native host plants makes it a frequent visitor to backyard gardens and open fields.
Description
Black Swallowtail Butterfly Identification.
Eastern Black Swallowtails are medium-sized butterflies with black wings and distinctive yellow and blue markings. Females typically display more extensive blue coloration on the hindwings, while males have more prominent yellow spots. The tails on their hindwings give them their 'swallowtail' name and serve as a key identifying feature.
They look similar to the Spicebush Swallowtail, however, the spicebush is missing one of the orange dots on the outside wing.
Too see the subtle differences, side by side, in the various black colored species, go to the Black Colored Swallowtail Comparison and Identification Guide.
Host Plants
Eastern Black Swallowtail caterpillars rely on host plants in the carrot family (Apiaceae). These include common non-native garden herbs like parsley, dill, and fennel, as well as non-native Queen Anne's lace. Providing these plants in your garden not only supports their life cycle but also ensures you'll see more of these beautiful butterflies.
Their native host plants are lesser known, and include Alexanders, Angelica, Wild Licorice, and Canadian Hornwort. Golden Alexanders are low maintenance and easy flowers to grow if you want to try your hand at a native host plant for these butterflies.
Plant Natives and they will come.
Habitat and Range
Native range map of the Black Swallowtail - Papilio polyxenes
The Black Swallowtails butterfly is found across the eastern and central United States, parts of southern Canada, and extending into Central America.
Due to the amount of native and non-native host plants in the Apiaceae family, they thrive in a variety of habitats, including open meadows, fields, gardens, and roadside areas.
Adults and Flights
Eastern Black Swallowtail adults are active from spring through early fall, typically producing 2-3 generations (flights) per year. They are fast fliers and can often be seen visiting flower gardens, where they sip nectar from a variety of blossoms, including milkweed, coneflower, and other native plants.
Black Swallowtail Caterpillars - Eggs, Instars, and the Chrysalis
Two Black Swallowtail eggs on non-native Queen Anne's Lace. They look like tiny yellow balls on the underside of host plant leaves.
The caterpillars of the Eastern Black Swallowtail undergo five instars as they grow. Early instars are small with little spikes. They also have a small white mark near their
centers which makes them look a little like bird poop.
Later instars develop their characteristic bright green coloration with black bands and yellow spots. When threatened, the caterpillars deploy their osmeterium, an orange/yellow, forked gland that emits a foul smell to deter predators.
When they leave their host plant to pupate into a chrysalis, they will travel up to 30 feet to find a spot to pupate. I've personally seen one pupate 60 feet from its host, so they can travel quite far!
They will remain in the chrysalis for roughly 10 - 20 days. In the fall, they will overwinter and emerge in the spring.
This is a 5th instar Black Swallowtail caterpillar on my tiny 2x3 foot fennel patch. Each year I get up to a dozen caterpillars on it.
Black Swallowtail Caterpillar leaving it's fennel patch to find a place to form a chrysalis. This day, 8 caterpillars left the small fennel patch to pupate. One traveled an amazing 60 feet before finding a spot!
How to Attract and Support Spicebush Swallowtails
To attract and support a population of Eastern Black Swallowtails, plant a variety of their host plants, such as parsley, dill, and fennel, in your garden. If you get caterpillars, there is usually enough of these herbs for both you and the caterpillars.
The easiest way to start a fennel or dill patch is with seeds. The first year the fennel will be small, but once the taproot develops, they will grow to a height of 4-5 feet each year! Each year the dill and fennel will also reseed itself.
I have mine in a small 2 foot tall fence to keep rabbits from munching them down.
Native host plants include Alexanders, Angelica, Wild Licorice, and Canadian Hornwort. If you want to try your hand at a native host plant, try Golden Alexanders. They are low maintenance and easy to grow flowers.
Since all swallowtails overwinter on twigs and leaf piles, leave the leaves around your trees and shrubs, or you will kill your population of swallowtails.
Providing nectar-rich flowers like zinnias, milkweed, and clover will also help sustain the adult butterflies. Avoid using pesticides, as they can harm both caterpillars and adult butterflies.
Recommended Butterfly Rearing Items:
Note: Raise butterflies for educational purposes only as it's best to leave them on the native plant. If you do raise them, please keep them outside. do not raise them indoors.
RESTCLOUD Insect and Butterfly Habitat Cage
This butterfly tent is sturdy and tall enough for milkweed. It features five mesh panels for airflow with a clear vinyl window for watching caterpillars. It's ideal for monarchs and other butterflies, with a collapsible, reusable design and a large zipper opening for easy releases.
Short Peg Rack with 8 Large Floral Tubes to Feed Caterpillars Host Plant Cuttings
The short peg rack and water tubes are designed for caterpillar safety. The short pegs to prevent unsafe chrysalis formation. These tubes are ideal for holding milkweed and other host plant cuttings, supporting eggs, caterpillars, and nectar flowers for adult butterflies.
These are much better than the grid-style rack holders where the caterpillars can form an unsafe chrysalis.
Recommended Wildlife Restoration Books:
Gardening for Butterflies: How You Can Attract and Protect Beautiful, Beneficial Insects
The Xerces Society, 2016
The experts at the Xerces Society offer this guide to creating a pollinator-friendly garden that supports at-risk butterflies. This book teaches why butterflies matter, the threats they face, and how to design habitats where they will thrive, no matter your garden's size or shape.
These books below are by Doug Tallamy, a renowned entomologist and ecologist, widely recognized as the leading advocate for promoting native plantings in yards to support biodiversity and wildlife conservation.
Nature's Best Hope: A New Approach to Conservation That Starts in Your Yard
Douglas W. Tallamy, 2020
In this highly recommended book, Dr. Tallamy proposes a practical conservation approach, encouraging homeowners to plant native species and transform their yards into wildlife habitats with specific strategies that can be easily incorporated into their own yards! Available in Kindle, Hardback, and Audio.
The Living Landscape: Designing for Beauty and Biodiversity in the Home Garden
Douglas W. Tallamy, 2014
The Living Landscape teaches gardeners how to create a beautiful, functional yard that nourishes wildlife while providing space for play, privacy, and even a vegetable garden. It offers strategies for crafting a diverse, layered landscape with beauty, outdoor rooms, edible plants, and wildlife sustenance.Available in Kindle and Hardcover.
