05/10/2026
That's not a monarch caterpillar on your dill. The host plant is the identification.
Monarch caterpillars eat milkweed. Only milkweed. A caterpillar on your dill, parsley, fennel, or carrot tops is not a monarch — it's a black swallowtail. The two are sometimes confused because both have bold banding patterns, but they eat completely different plants and belong to different families.
The host plant is the fastest field ID for any caterpillar. 🌿
A black swallowtail caterpillar is bright green with black bands and yellow or orange dots within each band. It feeds on plants in the carrot family — dill, parsley, fennel, Queen Anne's lace, carrot tops, and celery. It curls into a J shape when disturbed and extends an orange forked osmeterium from behind its head, releasing a foul smell.
A monarch caterpillar has white, yellow, and black stripes in a consistent banding pattern. It feeds exclusively on milkweed. It never appears on dill or parsley.
The confusion matters because gardeners who find caterpillars on their herbs sometimes remove them — assuming they're pests. The black swallowtail caterpillar eats a small amount of foliage, pupates, and becomes one of the most common and beautiful butterflies in the eastern states.
🐾 Quick ID:
- On dill, parsley, fennel, or carrot tops = black swallowtail
- On milkweed = monarch
- Green with black bands and yellow dots = black swallowtail
- White/yellow/black consistent stripes = monarch
- Both are native. Both are beneficial. Neither is a pest.
The caterpillar eating your dill isn't a pest. It's a butterfly in progress. The herb recovers. The butterfly doesn't come back if you remove the larva.