Old World swallowtail caterpillar

Natural Habitat

Gardens, meadows, and hillsides across Europe, Asia, and North America; specifically found on host plants such as dill, fennel, and parsley.

Diet & Feeding

Herbivorous; primarily feeds on the leaves of plants in the family Apiaceae (umbellifers) such as wild carrot, fennel, dill, and milk parsley.

Behavior Patterns

Features a specialized defensive organ called an osmeterium—a Y-shaped gland that emits a foul-smelling secretion when the larva is threatened. It undergoes five instars before forming a chrysalis to undergo metamorphosis.

Risks & Benefits

Benefits the ecosystem as a primary consumer and later as a significant pollinator in its butterfly stage. It poses no physical risk to humans, though it is sometimes considered a minor garden pest for those growing herbs like dill or parsley.

Identified on: 3/18/2026