Finding a caterpillar feeding on parsley is a common experience that sparks curiosity about its identity. This encounter is a specific biological relationship between the herb and the larva of a particular butterfly species. The presence of these insects indicates your garden is serving as a host site for insect development. The creature responsible for consuming the parsley is almost always the same species.
Identifying the Parsley Worm
The caterpillar most frequently found on parsley is the larva of the Black Swallowtail butterfly, commonly referred to as the “parsley worm.” When fully grown, this striking caterpillar can reach up to two inches in length. Its body is lime-green, accented by prominent black bands and rows of yellow or orange spots.
This bold coloration warns predators, but the caterpillar also possesses a direct defense mechanism. When threatened, it extends a fleshy, forked, orange gland called the osmeterium from behind its head. This organ releases a foul-smelling substance derived from the host plant to deter small animals.
Why They Choose Parsley
The caterpillar seeks out parsley because the plant serves as a required host for its development. Parsley belongs to the Apiaceae family, which includes dill, fennel, and Queen Anne’s lace. The female Black Swallowtail butterfly specifically seeks out plants in this family to lay her eggs. These plants contain chemical compounds that the caterpillars have evolved to tolerate and require for growth. The larva ingests these compounds, utilizing the plant’s natural chemistry for the survival of its offspring.
The Journey to Becoming a Butterfly
After three to four weeks of feeding, the caterpillar reaches full size and prepares for metamorphosis. It leaves the parsley plant in search of a secure location to pupate, a phase known as the “wandering phase.” It anchors itself to a surface with silk and hangs in a characteristic “J” shape before shedding its final skin to reveal the chrysalis.
The chrysalis, or pupa, is typically pale green or brown, helping it blend with its background. The pupal stage lasts ten to twenty days in summer generations. However, the final generation of the year will overwinter in the chrysalis, emerging as a butterfly the following spring. The adult Black Swallowtail butterfly emerges with black wings featuring rows of yellow spots and distinct blue markings.
Coexisting with the Larvae
Finding caterpillars feeding on parsley often involves simple coexistence for herb gardeners. Since the larvae are the early stage of a beneficial pollinator, many gardeners allow them to complete their cycle. Because a single caterpillar consumes significant foliage, planting extra parsley specifically for the butterflies is a common practice. If a small plant is heavily consumed, the caterpillars can be gently relocated to another host plant like dill or fennel. This allows the larva to continue development without completely stripping the initial herb, supporting the local Black Swallowtail population.