This post may contain affiliate links. If you make a purchase through links on our site, we may earn a commission.
When you see a caterpillar on dill in your garden—or other plants—you may be startled, grossed out, or annoyed that your plant is being systematically decimated. I get excited. Because I know it’s a black swallowtail caterpillar (Papilio polyxenes) that’s going to turn into a beautiful butterfly. And that butterfly is going to become one of many valuable pollinators in my garden.
I see a few types of swallowtail butterflies fluttering about my property, landing on various annuals and perennials. They are among the largest and most common butterflies we see in our gardens—there are about 550 swallowtail species in the world! The black swallowtail (often referred to as the Eastern black swallowtail) can be found throughout much of North America.
The tails on the hind wings of a swallowtail butterfly look like that of a barn swallow, which is how they got their common name.
What is a host plant?
A lot of articles focus on plants that attract bees, butterflies, and hummingbirds. But it’s also very important to provide plants and trees for the larval caterpillar stages. These are called host plants. My article about butterfly host plants explains the importance of these plants in a butterfly’s life cycle.
What’s important to note is that every butterfly and moth species has its own host plant or plants where the female will lay her eggs. Once an egg has hatched, the baby caterpillar will eat the egg shell and then start to consume the host plant its on. The most famous host plant in recent years is milkweed. Milkweed plants are the only plants where a monarch butterfly will lay her eggs.
A female butterfly will lay her eggs in clusters or as single eggs, depending on the species. You will often find them underneath a leaf or along a plant stem.
Finding and identifying a caterpillar on dill or other black swallowtail host plants
Where I live in Southern Ontario, I have found caterpillars on my dill plants anywhere from early June to the end of August. There are two generations or broods of swallowtail butterflies over the growing season.
Finding the eggs is tricky—I usually end up just finding the caterpillars. But if you’re looking, the eggs look a bit like tiny yellow fish roe. Caterpillars go through five “instars” or stages of development. And they can look very different in their younger stages than when they’re plump and ready to form a chrysalis.
Through each instar stage, the caterpillar molts its skin. In the early instar stage, caterpillars look a bit like bird droppings, probably to deter predators. They’re black in color with orange dots and a white center, and it looks like they have little spines on their back. As they grow, the middle instar swallowtail caterpillar stage still includes spines, but the caterpillar is more black and white striped with yellow spots.
During later instar stages, the swallowtail caterpillar becomes a lime green color with black and yellow stripes. That spiny back disappears. And they are closer to forming a chrysalis. My hope is always that they pupate before the birds find them!
What to grow to feed black swallowtail caterpillars
One type of plant does not feed all butterfly caterpillars. They all rely on different, specific plant species, known as host plants. For example, the aforementioned milkweed is the only larval host plant of the monarch butterfly caterpillar. Black swallowtail caterpillars rely on members of the Apiaceae or Umbelliferae family, which include dill, carrot tops, parsley, fennel, rue, and Queen Anne’s lace.
There are also some native plant species that are host plants to black swallowtail caterpillars, including golden Alexander (Zizia aurea) and yellow pimpernel (Taenidia integerrima). The blooms of both resemble dill flowers.
My recommendation if you’re growing herb plants, like parsley and dill, is to spread out your plants in different places of the garden. That way you’ll have lots to enjoy on your plate and the swallowtail caterpillars will have lots to enjoy as they move through their instar stages.
What to do if you see a caterpillar on dill and other host plants
The short answer is to let them eat! The other answer is grow more of what they like to eat if their appetite is interfering with your crops. I let my dill go to seed in the garden, so I have a LOT of dill plants from spring through fall. I simply pull the ones that get in the way of planting other veggies and herbs, but there is plenty left over for the caterpillars to eat—and to enjoy in my meals.
You can also (gently) move a swallowtail caterpillar on dill to another host plant, though they don’t like to be moved when they’re ready to molt. When alarmed, what look like little orange antennae come out. And they’ll emit an odor to warn off whoever is disturbing them. Those “antennae” are actually an organ called an osmetierium, a warning sign for predators.
It’s unlikely you’ll see a black swallowtail butterfly emerge from its chrysalis in your garden, but hopefully you see the butterflies enjoying the nectar provided by your garden. Unlike caterpillars, the butterflies are not as picky about what they eat.
More pollinator-friendly advice, identification, and growing tips
The book Gardening For Butterflies by the Xerces Society is helpful when it comes to identifying the types of butterflies you may find in your garden, as well as what to plant to support both the caterpillar and butterfly stages of life.
- Foraging habitat for pollinators: What to plant in sun and shade
- Pollinator garden design: How to get started attracting bees, butterflies, and birds
- Attracting more bees and pollinators: 6 ways to help our native insects
- Types of bees commonly found in yards and gardens
- Hummingbird flowers to add to your garden
- Building a garden for caterpillars
- Planning a habitat garden
- Welcoming fireflies aka lightning bugs to your garden
I’m in my 70s, but always had them on our dill when I was a kid. When they got really plumped up we’d put a couple in a big jar with dill and a few sticks. We would then get to watch the whole process of them becoming a butterfly. It was fascinating.
I now live 3 stories up in a condo, but have a huge 1200 sq ft terrace. Every year I add more to my container garden. I have parsley every year, but never had the caterpillars before. I was thrilled when I found 2 today. They can munch their little hearts out.
As for the cabbage moth, I have bought covers for my radishes and kohlrabi. They absolutely destroy them. Sorry guys!!
Hi Jo, I’m so glad the caterpillars found your container garden! And I don’t blame you for keeping the cabbage moths out!
I love a happy ending. Just found a couple on my dill today.
I have a late crop of dill or a second crop either way it’s October and heading into the fall winter time in Wisconsin. There three caterpillars eating on the dill. I am so surprised that they are dealing with the cool temps. I don’t wan them to die and thinking of digging up the plants and bring then inside. Even if they do change into butterfly’s no where to go. What is the best thing to do…. let nature do it thing or help a being live out its life cycle. Temps are good for another week. I am a bee keeper I have done many things to help my bee continue to survive. B
How exciting for you! Swallowtails overwinter as a chrysalis so just leave them be. They will continue to feed on the plants as long as they need to, then they will crawl off and find a place to form a chrysalis and hunker down for the winter as a pupa to emerge as an adult next spring/summer. Do not bring them indoors.
Wasps. Yes they do. I had a mesh enclosed with baby swallowtails inside. I had put it outside on the porch for the afternoon and sadly left an opening. Big enough for those lousy little yellow jackets. They murdered the cats. I found them fallen off the plant with the little assassins still buzzing about. Grrrr. This year I have one that I am diligently protecting. I think it’s close to pupating.
Thank you for this informative article. We had a bunch of caterpillars feeding on our dill; we left them alone, and they fattened up nicely. But now the caterpillars are missing, and I don’t see any chrysalises. 🙁 Does that mean maybe birds ate them? Other possible explanations for them being MIA?
Hi J.C., I don’t usually see a chrysalis, a caterpillar will just disappear one day. It’s possible that a hungry bird came along (and one time there was evidence that had happened), but I like to think they’ve just found somewhere more out of the way to form a chrysalis.
Wasp enjoy eating them. I found two on my parsley plant after watering one morning. Before going in I looked at them and a wasp swooped in and snatched one up. I am now nurturing the other until it turns.
This is my 2nd summer raising Black Swallowtails. Last summer I fed them dill/parsley plants and had 30 caterpillars. The next day, half of them had disappeared. We have skinks (lizards) in the yard and I realized he was the culprit taking them as well as the birds. I raised only 5 to release. This year, I purchased a 36 inch tower mesh cage ($28 at Amazon) and placed it on a bench in the shade. I have raised and released 40 butterflies which was a joy to see. The female returns and lays more eggs. It takes time to keep the cage clean if you place potted herbs in there. I changed the parsley every few days when the leaves were eaten. I’ve heard a use of raised beds works for some people; easier to care for them. Garden center had the perennial Rue today and it is a much larger plant to feed them. I live in southeastern Va so it’s Sept and I still have plenty of caterpillars to fed. I did save my parsley/dill after they ate all of it but it is slowly growing back. Rue was recommended. Hopefully they will eat it. I will say it was exciting every week seeing new butterflies emerge in the mesh cage. Takes a few hours for their wings to dry then I release them. Tips: The chrysalis needs to be kept out of the sun in a shaded area until they hatch. Don’t release them at night or in the rain. Whether leaving the caterpillars in the garden or a mesh cage, it is a joy to see their beauty. Females will have blue markings on wings and males are mostly yellow. Females will come back to lay eggs on your herbs daily. Eggs are tiny cream eggs, turn black then tiny black caterpillars hatch. The warps are predators, too so I used a mesh cage. Good luck to everyone.
I just got done removing 6-7 of these from my dill and parsley plants and promptly went back out and put them back on the plants. Thanks for the info, I won’t make that mistake next year!!
I’m so excited- I live on the fifth floor of a condo bldg and I have a large balcony with a big parsley plant. Today I found 2 of these caterpillars and hope to see them become butterflies. Will buy another parsley plant for them. Great informative article.
Hi, I have a dill plant that was big and beautiful and now I see about 8-10 caterpillars eating and killing the dill plant. It is yellow and almost dead. What should I do?
It may bounce back once the caterpillars leave. I would get a replacement because I wouldn’t want to get rid of the caterpillars.
Hello
I have just discovered 5 caterpillars on my fennel
Should I expect them to travel to other herbs in the garden ?
Hi Kelly, It depends on what you’re growing. If you have dill or parsley, they may travel to them, as well.
I have 8 caterpillars on my dill plant. It’s in a pot on my deck about 15 feet from the rest of the garden. Should I move the pot into or closer to the garden so they don’t have to travel 15 ft over the deck to find a spot to form a chrysalis?
Hi Rose, It’s up to you… they usually wander away from the food to form a chrysalis somewhere safe.
Hi! I was excited to come across your article about the swallowtail butterflies. I have over a dozen caterpillars in various stages of development in my garden on the dill. I left them except the ones on the dill that I was removing which I relocated to other dill that was still growing. I love watching them in their various stages of development.