Eastern Black Swallowtail Butterflies Everywhere: Here’s How to Raise Them at Home

Monarchs generally make headlines, but the Eastern Black Swallowtail caterpillar and butterfly also merit attention.  Especially in this mild, wet year.

Swallowtail Monarch caterpillar
Frequently confused in the late caterpillar stage: Swallowtail, on the left on rue, Monarch, on milkweed on the right. Photo by Monika Maeckle

In my downtown plot, every fennel, dill and rue plant is loaded with Eastern Black Swallowtail caterpillars. Even along the Llano River, we’re finding hungry Swallowtail cats on wild carrot and parsley.  One hungry critter decimated three newly-planted Finochio seedlings down to the nub.  Yes, butterfly gardening is full of compromises–like sharing your herbs and edibles with a slew of hungry caterpillars.

Swallowtail fennel
Down to the nub! Swallowtail caterpillar devoured three new Fennel seedlings. Photo by Monika Maeckle

That said, just like Monarchs, Eastern Black Swallowtails wear black, green, yellow and white-striped suits in their later caterpillar stages, and are fun to raise at home.  Unlike Monarchs, they make an amazing saddle-type chrysalis, sport amusing tentacle-like “tubercles” that reveal themselves when disturbed, and are vexing in their unpredictability.

Since several readers haved asked about raising Swallowtails this season, we’re recycling a post from July, 2014, that offers tips on how to do it.

How to Raise Eastern Swallowtail Butterflies at Home

Monarch butterflies get all the press, but the Eastern or Black Swallowtail, Papillio polyxenes, a large blue, black and gold and cream-specked beauty, flies in our neck of the world from April through November.   The Texas native provides lots of action in the garden when Monarchs are elsewhere.

Eastern Swallowtail
Eastern Swallowtail, recently hatched, resting in the grass. Llano River, Texas Hill Country. Photo by Monika Maeckle

We’ve been getting questions about raising Swallowtail butterflies in recent weeks. The wet June has made for a long season for dill, fennel, parsley and rue the plants on which Swallowtail butterflies lay their eggs.  Below are tips for raising them at home.

Eastern Swallowtail egg on Dill Weed
Eastern Swallowtail egg on Dill Weed.  Photo by Monika Maeckle

First, locate the eggs. The tiny yellow spheres perch prominently on the leaves of dill, fennel, parsley and rue. Check your plants frequently, as wasps, ladybugs, spiders and others will slurp up these protein pops as soon as they are spotted.

When you’re looking, you may notice some clear, dry, empty spheres, exactly the size of the eggs.  Those are empty egg shells already visited and consumed by predators.

Swallowtail egg
Close-up of Swallowtail egg on dill. Photo by Monika Maeckle

I usually snap off a piece of the plant with the eggs on them and take them inside to rest in a jar with the lid loosely closed.  Don’t worry about “smothering” the egg.   They’ll do fine until they hatch, usually within four days.

Once the little guys hatch, you’ll want to provide fresh air to prevent mold from growing on the host plant.  Bring in some sprigs of fresh plant and put them in the jar. I usually leave the eggs alone until the caterpillars are big enough to spot with a naked eye–generally two days.

You’ll see they’re tiny and hard to monitor, so again, leave them alone and just provide fresh air and fresh host plant until they grow bigger.

After a few days, you’ll see a small black creature, perhaps 1/16th of an inch long.  If you look closely, you might notice a white or orange band in the middle of the body.

That’s your first instar, or stage, Swallowtail caterpillar.  They will eat quietly and consistently for several days before they morph to the next stage.   They’re rather nondescript and not yet as interesting as they will become.  Just wait.

First instar Eastern Swallowtail caterpillar on rue. Photo by Monika Maeckle

Up until this point, I may have had the Swallowtails in a jar or container with a loose lid or netting.  But now it starts to get interesting and I like to watch them eat and grow, although it can make a small mess.

Usually I gather fresh host plant and put it in a vase with newspaper underneath so I can observe the caterpillars literally grow before my eyes. The newspaper catches the frass, or caterpillar poop, that the caterpillars produce in volume.

The small, black odorless pellet-like droppings may seem gross, but they’re actually not.  Well, maybe for some people.  Generally I will set such a vase in a highly trafficked place in my home or office so I won’t miss the action in the course of any day. (Yes, I’ve been known to take caterpillars to work.)

Swallowtail bouquet
Bouquet of Swallowtail caterpillars in vase on fennel. Photo by Monika Maeckle

The caterpillars will continue to eat and morph for about 10 days.   What’s amazing is how different they look at each stage.

As they move through their instars, they completely transform, going from the unremarkable black cat with a white band to a prickly orange, white and black form, then to a black, green, yellow and white-striped creature often confused with Monarch caterpillars.

Throughout the process these boys eat voraciously–lots of fresh host plant.  In our hot Texas summers, I find dill expires early in the season but that Swallowtails will easily transition to the more abundant and heat-hardy rue or fennel.

At the ranch we have wild parsley and I have brought that home for feeding.  Once I bought organic fennel or parsley at the grocery store to feed a slew of Swallowtails when I had run out of fresh host.  The caterpillars didn’t seem to like it much (like us, they prefer FRESH greens) but they ate it in the later stages.

Swallowtail showing tubercles
Who goes there?!? Note the yellow “tubercles” which the Swallowtail shows off when bothered. Monarchs don’t do that. Photo by Monika Maeckle

One of the most amusing aspects of raising Swallowtails is their interesting tentacles.  When they get to the last stages, they show distinctive yellow antennae when poked or bothered.

This orange forked gland, called the osmeterium, shows itself when the butterfly perceives danger.  Upon the slightest nudge or threat, the yellow tentacles pop out of their head and emit a distinctive, sickly sweet odor. Kids are always impressed when you provoke the Swallowtail’s tentacles.

Swallowtail caterpillar sheds its skin. Photo by Monika Maeckle
Swallowtail sheds skin. Photo by Monika Maeckle

The caterpillars will continue to eat, shed their skins and morph to the next stage over about 10 days until they get to the fifth instar at which time they will cease eating and seek a quiet place to form their chrysalis.

Swallowtails are famous for wandering far from the host plant and taking their time to emerge from the chrysalis at unpredictable times.  Monarch caterpillars are generally reliable in taking 10-14 days to eclose, or make the transition from chrysalis to butterfly.

Swallowtails, in contrast, can take a few weeks to many months to emerge.  Their unpredictability is also manifested in the varied color of the chrysalis that results from the final morphing.   Sometimes brown, sometimes green, you just never know what color a Swallowtail chrysalis will be.

Swallotwails wear chrysalis coats of many colors. Photo by Monika Maeckle

Because Swallowtails can wander, it’s smart to contain them in a cage when they get large enough to bust their stripes and go chrysalis.  I use a net laundry hamper and simply put the vase inside.

The Swallowtail will bow its head and make a silk button and saddle before going chrysalis. Photo by Monika Maeckle

The Swallowtail, when ready, will stop eating.  He will bow his head in an upside down J-shape, and spin a silk button to attach itself by its head to a twig, branch or net siding.   He then makes a silk saddle to hold itself snugly in place for the time it takes to transform its DNA into a butterfly–again, an often unpredictable amount of time.   Some Swallowtails will overwinter to the next season, depending on the conditions present at the time of forming the chrysalis.

Newborn Swallowtail butterfly with sister chrysalis. Photo by Monika Maeckle
Newborn Swallowtail butterfly with sister chrysalis. Photo by Monika Maeckle

When the day finally comes, though, you will know because the chrysalis will turn dark, then clear. Thereafter, the Swallowtail will emerge when ready.

Give it a few hours to allow its wings to harden. When she starts beating them slowly, you know she’s ready for flight. Take her outside and send her on her way.

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20 Responses

  1. Alex Folger
    | Reply

    It’s the beginning of August and one of mine hasn’t turned into a chrysalis yet. Should I be worried?

    • Monika Maeckle
      | Reply

      They’re VERY unpredictable. Patience. How long has it been and where are you located?

  2. Jim & Pat Isaacs
    | Reply

    we till our dill /garden under late fall and sow a green crop for the winter. If I collect the dried plants where should I hang them? In the barn? We live on the state lines between NC/SC Piedmont area. Thank you!

  3. Deborah Garcia
    | Reply

    Great information. I have been searching your site to see if I can find tips for over-wintering Black Swallowtails. I currently have 2 in chrysalis for almost 3 weeks now. Do you have some advice on how to care for these right now? This would be my first time with the possibility of overwintering.

    Thanks in advance
    Debbie Garcia

    • Monika Maeckle
      | Reply

      Maybe must them occasionally if it’s dry. They can remain in chrysalis form for months!

  4. Meldon Bishop
    | Reply

    i just found 20 cats and was not sure what to do so this helped.

  5. Tiana
    | Reply

    I have had so many cats this year. They have eaten down 2 dills and no one has anymore here in north Texas. So I still have parsley and have transferred to parsley , bronze fennel and bought a rue. They have eaten the new rue down in 1 day. I had at one time 13 cats, and 18 eggs. Down to 5 large cats and lots of babies. I wondered where they had gone. It seemed like every day I would lose a couple. Though predators. But today I saw 2 leaving a full parsley plant and take off. Pretty fast across the driveway. I did get them and put them in a jar with sticks and plant material. No fresh plants. Going to grocery.

  6. Patti
    | Reply

    I gave 9 swallowtail chrysalis from September and only 1 has emerged. Should I do anything to help them. Must or put outside? Temps are 70 today in Perry ks

  7. Miriam
    | Reply

    I planted a pot of dill on my porch and recently noticed the caterpillars on it. There were 3 now I’ve got two. They’re looking pretty plump for early Jan but it’s been pretty warm in SoCal and they have eaten their way through most of the stalks. There’s a few stems left. Assuming they’ll just hang out they’re done?

    | Reply

    I have cats contained eating parsley. They are over ten days old. Should I place the cage outdoors? I’m worried indoor air may be too dry and they need to acclimate to outside.

    • Ed Leafe
      | Reply

      I keep the parsley in a container of water, so the environment isn’t very dry. Even though I’m pretty new at this, I’ve raised 2 crops of cats all the way to adults, and I think keeping them indoors and away from predators is a huge advantage for them.

  9. Ed Leafe
    | Reply

    Wonderful article. I’m currently on my third “crop” of swallowtail caterpillars. I take bunches of fresh organic parsley in a small vase, and let them chomp away. My question is how do you handle the occasional case where a caterpillar falls off the end of a stalk onto the paper below the vase? Unless they look to be ready to chrysalize, I pick them up and replace them on their food. Do you do that too, or let ’em fend for themselves?

  10. Darlene H
    | Reply

    Loved reading your article. I have many milkweed plants in my yard and always have Monarchs flying around. I’m going to start planting rue, fennel and parsley for the Swallowtails. I have large dill plants but have never seen eggs on it. Is cilantro a host plant, also?

  11. Micah
    | Reply

    I love this article!! Great pictures… And you are not crazy to take them to work with you! I have done the same thing. 😉

  12. Sue
    | Reply

    I really enjoyed reading about the Swallowtails, Monica. Thank you!

  13. Crystal
    | Reply

    I’m a butterfly breeder and every year we raise these after the second round we have crashing. Any suggestions ?

  14. Emily
    | Reply

    we have been keeping swallowtails for a few years now. Located in central ontario, I’ve always been curious as to where the butterflies go. This year , 1 of our chrysalis , over-wintered, covered in ice and snow all winter, it’s now very much alive ( it wiggles). I’m excited to see the butterfly. I’m just not sure of if they migrate?

  15. Sean Foley
    | Reply

    I want to create a good garden spot for butterflies especially the Monarch. I know the Monarch prefers milkweed. Where can I buy milkweed?

  16. leslie@adamandleslie.com
    | Reply

    Do these grow in california too? Should I be planting this type of fennel?

  17. chris aka monkey
    | Reply

    cats are so interesting, i love watching your photos transform thanks xx

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