Identifying the Common Black Swallowtail (Papilio polyxenes)

Habits and Traits of the Black Swallowtail Butterfly

Black swallowtail butterfly.
Black swallowtail butterfly. Flickr user John Flannery (CC-ND license)

The black swallowtail, one of North America’s most familiar butterflies, frequently visits backyard gardens. They are a very common sight and you've likely seen the butterfly and caterpillar quite often, especially near your vegetables. 

How to Identify Black Swallowtails

This large butterfly has black wings with yellow markings and a wingspan of 8 to 11 centimeters. The male displays a row of bold yellow spots, while the female’s spots are faded shades of yellow and blue.

The black swallowtail’s colors mimic those of similar species, such as the giant or pipevine swallowtails. To identify the black swallowtail, look for a pair of black dots centered in larger orange circles on the inner edge of the hind wings.

The black swallowtail caterpillar changes appearance each time it molts. In the last few stages of growth, it is white and green with black bands and yellow or orange spots.

The black swallowtail is also known as the Eastern black swallowtail, the parsley worm, and the parsnip swallowtail. The last two names refer to the insect's proclivity to feed on plants in the carrot family.

Black swallowtails fall into the Papilionidae family, which includes other swallowtails:

  • Kingdom – Animal
  • Phylum – Arthropoda
  • Class – Insecta
  • Order – Lepidoptera
  • Family – Papilionidae
  • Genus – Papilio
  • Species – polyxenes

What Do Black Swallowtails Eat?

The butterflies feed on nectar from flowers.

Caterpillars feed on plants in the carrot family, which includes dill, fennel, parsley, and carrots.

Life Cycle

Like all butterflies, the black swallowtail undergoes a complete metamorphosis. The life cycle has four stages: egg, larva, pupa, and adult.

  • Egg - It takes 3-5 days for eggs to hatch.
  • Larva - The caterpillar has five instars (stage between molts).
  • Pupa - The chrysalis stage lasts 9-11 days, or over the winter.
  • Adult - Northern areas have one or two generations; southern areas may have three.

Special Adaptations and Defenses

The caterpillar has a special gland called an osmeterium that emits a foul odor when it is threatened. The orange osmeterium looks like a forked snake tongue. Caterpillars also ingest oils from the host plants of the carrot family; the foul taste of the chemical in their bodies repels birds and other predators.

The chrysalides of the black swallowtail can be green or brown, depending on the color of the surface to which they are attached. This form of camouflage keeps them hidden from predators.

The adult butterfly is thought to mimic the pipevine swallowtail, which is distasteful to predators.

Habitat and Range of Black Swallowtails

You will find black swallowtails in open fields and meadows, suburban yards, and roadsides. They are most common in North America east of the Rocky Mountains. Their range extends south all the way to the northern tip of South America and they are also present in Australia.