Anise Swallowtails

September brings beautiful bright green caterpillars to Carolyn Herriot's garden.

Credit: Carolyn Herriot

The fennel plants were covered with several beautiful bright green caterpillars with dark bands with yellow splashes in September. These are the larval stage of the common Anise Swallowtail butterfly, Papilio zelicaon, which is native to western North America. papilio zelicaon This stunning caterpillar’s major food plants are members of the Umbelliferae family, angelica, dill, fennel and lovage. If disturbed the caterpillar suddenly displays bright orange osmeteria or “stinkhorns” from behind its head. Used for defense, these glandular structures give off a foul odour. This caterpillar grows to around 5cm in length before forming a brown chrysalis about 3cm long. The chrysalis hibernates through the winter before beginning the lifecycle of a new Anise Swallowtail butterfly.