People often confuse the Black Swallowtail caterpillar with Monarch caterpillars, especially when they look the most similar. There are some main differences to look out for.
The Black Swallowtail caterpillars have thicker, green stripes and yellow, wavy “dots”. They also don’t have the long tentacles on their head and tail end like Monarch caterpillars do.
The most telltale sign is that Monarch will be eating on Milkweed while Eastern Swallowtails will be nibbling on plants of the Carrot family (dill, fennel, rue, Queen Anne’s lace, celery, parsley etc.)
Host Plants of the Eastern Black Swallowtail
Adult Eastern Black Swallowtails will lay eggs on plants in the Carrot family. You may find the caterpillars eating on these plants in great numbers but don’t be alarmed! There are several ways to keep the caterpillars happy while also saving some of the plant for yourself!
How to keep the caterpillars happy and not lose all of your plants or resort to using pesticides!
1. Plant extra dill or fennel so that there is enough for them and you to eat.
2. Pick the caterpillars off of the plant and put them into a butterfly enclosure with the host plant to watch them pupate and eclose into a beautiful butterfly.
3. Successional planting of dill/fennel/parsley etc. throughout the summer so there is always enough to go around.
Lifecycle of the Black Swallowtail
Similar to the Monarch butterfly: The female butterfly lays one yellow egg at a time on a host plant. After 4-9 days, a caterpillar (larva) hatches from the egg. Over 10-30 days, the caterpillar grows through 5 different stages (called instars) to a length of 2 inches.