The round egg is pale green, later turning orange brown. Young caterpillars are black with lighter colored transverse stripes. Older larvae have two color forms. The more common form is green with yellow and white transverse stripes; the rarer form is black and banded with white and orange. In both forms, between the swollen thorax and the abdomen, there is a yellow, black, and bluish-white band. The larva has a yellow, foul-smelling, forked gland called an osmeterium which it will use to deter predators, especially spiders and ants. The chrysalis is either green or brown, and is more compact compared to chrysalids in the genus "Papilio". Three small horns project from the head and thorax. The chrysalis hibernates in areas of its range with cold winters. The zebra swallowtail caterpillar feeds only on species within the genus "Asimina". Commonly used species include "A. angustifolia" (slimleaf pawpaw), "A. incana" (woolly pawpaw), "A. parviflora" (smallflower pawpaw), "A. reticulata" (netted pawpaw), "A. tetramera" (four-petal pawpaw), and "A. triloba" (common pawpaw). "P. marcellus" caterpillars ingest chemicals called annonaceous acetogenins from their host plants, which are retained in the body tissues of both the caterpillar and the adult, and may help chemically protect the butterfly from birds.