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 (Papilio polyxenes) caterpillar 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 numerous 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.
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. And Jessica also wrote an article listing plants that are larval food sources for some of North America’s butterflies. Today I’m going to focus on identifying and feeding black swallowtail caterpillars.
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 plant species, known as host plants. For example, 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 plant a few in different places in 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 my 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—and 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 emit an odor. Those “antennae” are actually an organ called an osmetierium, which is used to warn predators.
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.
- The monarch butterfly host plant: Milkweeds and how to grow them from seed
- 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
Beautiful article. Have seen queries on facebook from people who want to know what to do with the cats they find, not knowing what they are. I like to plant extra parsley and dill to lure them in…so beautiful
This philosophy should extend to other caterpillars as well. Shift to thinking of them as baby butterflies or moths if that helps bring a positive change to your perspective.
With the exception of a rare army worm outbreak (which your county extension dept will handle) , these host plants evolved with Caterpillar herbivory activity and it won’t kill the plant. Even when pipevine cats eat every leaf, the plant bounces back very quickly.
Great article… I have two 3×8′ raised beds and ONLY grow wild flowers, parsley, dill and milkweed for caterpillars… black swallowtails, monarchs and yellow sulphurs. I also live in a bird sanctuary and have 6 feeders away from the gardens and have bluebird, mockers, warblers, thrashers, wrens, etc., which I feed mealworms. Tho I feed the birds I worry about them eating the caterpillars. How do I protect them or should I just let nature take its course? Thanks.
As sad as it is, I just let nature take its course.
Wonderful article! Very informative and helpful. Thank you!
I’m sorry I read the article after I threw them over the terrace! I hope they landed on the shrubbery below.
This article was very informative. I live on the coast of Eastern Central Florida. I’ve planted Dill, Fennel, Parsley, Rue and several flowering plants that Swallowtails love.
I have everything EXCEPT the Swallowtails! How else can I attract them? Is there a “Season” for Swallowtails? Even in Florida?
Hi Kathryn,
There are swallowtails in Florida, but I’m not sure when they’re most prevalent. I would look for a regional newspaper or online article to learn more about the swallowtails where you live. 🙂
Ashamed to admit that I made Diane’s mistake (previous post). Found tiny worms on both my parsley plants as well as my dill. Yep, threw them in the grass not knowing that the plants would recuperate. Then I researched and won’t do that again. I’m a brand new Gardner dabbler. Thanks for educating me.
Well, here it is, the end of October and I’m cleaning out my garden which has a lot of dill, planted just for the butterflies. And what did I find? A caterpillar. What do I do with it? I left it outside, but found some baby dill still growing, so I put it on that and the last I saw, it was munching away quite happily. Do I leave it outside all winter? Bring it in? What? Please help both of us. Please reply by e-mail if possible. Thanks
Hi Betsy, I think you should probably leave him and let nature do its thing. If you bring him inside, you’ll then have to raise a butterfly all winter…
I found a black swallowtail caterpillar on dill in my garden this week, but the nights are down in the low 30’s and daytime highs in the mid 50’s. And of course, the temps will be dropping more soon. What should I do with him? He’s still small and dark. Should I leave him outside by the dill (which is pretty much done for the season) or bring him in and provide dill inside? I’d love to keep him alive if possible! Thanks! 🙂
Hi Leah, It’s probably best to leave him outside… if you bring him inside, you’ll have a butterfly to care for all winter…
Hello Leah, you did not have to leave the caterpiller outside. Nor would you have to take care of a butterfly all winter. Butterflies do not live in the winter. The caterpiller would soon form a Chrysalis and stay dormate all winter in the Chrysalis cocoon. And emerge in the spring. Most all butterflies only live 10 to 20 days but in that time can lay 200 to 400 eggs. Some species do live 45 days. Only about 1 in 100 make it to become a butterfly. Most will be spotted by birds.
I have some caterpillars about to wrap up for the metamorphosis going into that shape and still on the dill. It’s time to plant other things where that dill is. I’ve been happy to let them eat as much as they want and holding out removing the flowered dill waiting for them to finish and move along to chrysalis elsewhere. It seems they like it on the dill too much & want to stay on. Once they go into chrysalis, would they be ok if I gently cut the dill plants out of the garden and put them nearby to finish out until they emerge as butterflies? I would think so, yet I’m ignorant on butterflies. Thank you for sharing your knowledge!
Hi Kelly, I find that when they’re ready to form a chrysalis, the caterpillars usually disappear from the garden and I don’t see where they end up. But if you do happen to spot one, I have found some videos online that explain how to safely move a chrysalis.
Am I able to keep caterpillars of different stages together?
I think so… I’ve seen them in nature on one plant together…
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.
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.
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.
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.
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.
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!!
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.
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.