Invertebrates
Black Swallowtail
Papilio polyxenes · also called eastern black swallowtail, parsleyworm
A gardener reaches to pick a black swallowtail caterpillar off a parsley plant, and the caterpillar responds by suddenly extending a bright orange, forked organ from behind its head, releasing a smell unpleasant enough to make most hands, and most birds, reconsider immediately.
Overview
The black swallowtail, Papilio polyxenes, is a bold black-and-yellow butterfly native to grassland, garden, and open habitat across a broad range of North and Central America. Its caterpillar’s foul-smelling defensive organ and close association with garden herbs make it one of the more commonly encountered and easily raised butterflies in home gardens.
A defence that trades looks for smell
Rather than relying on camouflage or speed, a threatened black swallowtail caterpillar briefly transforms its own appearance, flashing a startling orange organ paired with an unmistakably unpleasant odour that gives most predators every reason to look elsewhere for a meal.
Status
Least Concern — widespread and common across suitable grassland and garden habitat throughout North and Central America.
Black Swallowtail: common questions
Why does a black swallowtail caterpillar have an orange, fork-like organ?
A black swallowtail caterpillar can extend a bright orange, forked organ called an osmeterium from behind its head when threatened, releasing a foul smell strong enough to deter birds and other predators, a defensive display that briefly transforms the caterpillar's appearance to startle an attacker.
Why is the black swallowtail caterpillar called the parsleyworm?
The black swallowtail caterpillar is sometimes called the parsleyworm because it commonly feeds on garden parsley and other closely related host plants such as dill and Queen Anne's lace, a habit familiar to many home gardeners who grow these herbs.
Is the black swallowtail easy to raise at home?
Yes, the black swallowtail is a popular species for people raising butterflies at home, since its caterpillars readily accept common garden herbs such as parsley and dill as food, making the full life cycle relatively easy to observe from a home garden.
Where does the black swallowtail live?
The black swallowtail is native to grassland, garden, and open habitat across a broad range of North and Central America, generally found wherever its carrot-family host plants are available.