What Eats Black Swallowtail Caterpillars: Meet Their Predators

Black swallowtail caterpillars are fascinating creatures known for their striking appearance and the plants they consume, such as carrots, parsley, dill, and fennel.

These colorful caterpillars are an essential part of the ecosystem, but they also face various predators that can harm or even eat them.

As you learn more about the life of black swallowtail caterpillars, it’s crucial to understand the predators that threaten their existence.

In doing so, you’ll gain a deeper appreciation for the delicate balance within the world of these caterpillars, and perhaps even find ways to protect them in your own backyard.

What Eats Black Swallowtail Caterpillars
Parsley Worm or Black Swallowtail Caterpillar

Life Cycle of Black Swallowtail

Eggs and the Larval Stage

When the adult female Black Swallowtail Butterfly is ready to reproduce, she will lay eggs on the larval host plants. The yellow eggs eventually turn dark before hatching.

As a caterpillar, the early instar larvae are black and spiny. The Black Swallowtail Caterpillar, also known as the parsleyworm, can be various shades of green with narrow black bands on each body segment.

Additionally, these black bands are interrupted by yellow-orange dots. They consume leaves and flowers from plants in the carrot family, such as cultivated carrot, parsley, dill, and fennel.

Throughout this stage, your caterpillar will molt several times, allowing it to grow.

Here are some key features of the larval stage:

  • Green with black bands and yellow-orange dots
  • Consumes leaves and flowers from plants in the carrot family
  • Molts multiple times to grow
Parsley Worm

Pupal Stage

After reaching a length of about 2 inches, the caterpillar will then enter the pupal stage, also known as the chrysalis phase.

During this time, the caterpillar undergoes a remarkable transformation into an adult butterfly. It forms a chrysalis where it remains until it emerges as a fully developed Black Swallowtail Butterfly.

The process typically takes about two weeks, but some individuals may enter a state called diapause, where the process is delayed to avoid unfavorable environmental conditions like extreme temperatures.

Let’s compare the two stages in a brief table:

Larval (Caterpillar)Green, black bands, yellow-orange dots, consumes plants in carrot family, molts to grow
Pupal (Chrysalis)Transforms into adult butterfly, enclosed in chrysalis, can enter diapause if necessary

Throughout the life cycle of the Black Swallowtail Caterpillar, it is important to remember that the caterpillar stage is vital to the development of the adult butterfly.

By understanding the different stages, you can better appreciate the remarkable changes this species undergoes during its lifespan.

Adult Black Swallowtail

Black Swallowtail’s Host Plants

Common Host Plants

Black Swallowtail caterpillars are known to feed on a variety of host plants, most of which belong to the carrot family (Apiaceae). Some of the most common host plants that you will find them on include:

  • Parsley: A popular culinary herb with bright green leaves.
  • Dill: Another culinary herb with delicate, feathery leaves and yellow flowers.
  • Fennel: A plant with feathery leaves and yellow flowers, used both for its seeds and leaves in cooking.
  • Carrot: A common root vegetable with green, feathery leaves.
  • Queen Anne’s Lace: A wildflower with lacy, white flowers.

Preferred Leaves and Flowers

While the caterpillars feed on various plants within the carrot family, they do tend to have preferences.

Most often, they can be found consuming the flowers and leaves of their host plants. For example, the Black Swallowtail caterpillar (parsleyworm) is known to favor the leaves and flowers of parsley, dill, and fennel plants.

In addition to plants from the carrot family, Black Swallowtail caterpillars may also occasionally use plants from the citrus family and rue family as host plants.

However, they typically prefer members of the carrot family over these alternatives.

When searching for a host plant, the caterpillars are highly attracted to plants with:

  • Abundant, fragrant leaves
  • Bright yellow flowers
  • Easy access to leaves and flowers for feeding

When providing host plants for Black Swallowtail caterpillars, consider incorporating a variety of these preferred plants in your garden to support their growth and development.

Black Swallowtail Caterpillar

Habitats of Black Swallowtail

The black swallowtail is a beautiful butterfly native to North America, commonly found in various habitats across the United States, southern Canada, and even parts of Mexico1.

This elegant butterfly favors open areas, such as fields, meadows, parks, wetlands, prairies, and sunny backyards2. In the United States, they are typically found in states like Florida, Arizona, Texas, Iowa, Wisconsin, and New Jersey3.

In spring, black swallowtails are often seen in gardens and other cultivated areas, where their caterpillars feed on plants like dill, fennel, and parsley4.

Their range extends from the Rocky Mountains to southern Canada and from California to the east coast5. If you’re lucky, you might even encounter them in more arid regions like parts of South America6.

Some of the most notable features of black swallowtail habitats include:

  • Wide range of natural and cultivated environments
  • Presence throughout most of North America
  • Open areas with plenty of sunlight and plant life

So, if you’re a butterfly enthusiast or a gardener looking to attract these beautiful creatures, consider planting some of their preferred host plants and creating a welcoming environment for them.

You just might find your garden graced by the presence of black swallowtails!

Black Swallowtail Caterpillar

What Eats Black Swallowtail Caterpillars: Predators and Defense Mechanisms

Common Predators

Black swallowtail caterpillars, or Papilio polyxenes, have several predators that you might encounter. Some of the most common include:

  • Wasps
  • Spiders
  • Ladybugs

These insects are attracted to the caterpillars as a food source, but the caterpillars have developed ways to protect themselves from being eaten.

Defense Mechanisms

One of the key defense mechanisms of the black swallowtail caterpillar is the osmeterium. This is a unique organ that is present in all Papilionidae caterpillars, including both Papilio polyxenes and Battus philenor.

The osmeterium plays an important role in their defense mechanism:

  • Osmeterium: When the caterpillar feels threatened, it everts a forked, fleshy organ called the osmeterium from its head. This organ releases a strong, unpleasant odor, which is designed to deter predators from attacking.

In addition to the osmeterium, black swallowtail caterpillars exhibit some other defense mechanisms:

  • Distasteful: Black swallowtail caterpillars feed on plants from the Apiaceae family, which results in the caterpillars storing certain chemicals within their body. These chemicals make them distasteful to predators like spiders, wasps, and ladybugs.

  • Avoidance: Based on their appearance and the fact that they can be classified as a pest, black swallowtail caterpillars are indirectly protected as predators may avoid eating them. Their green coloration also helps them blend in with their surroundings, making it more difficult for predators to find them.

By utilizing these defense mechanisms, black swallowtail caterpillars are able to evade their predators and continue the life cycle to become beautiful black swallowtail butterflies.

Identifying Black Swallowtails

Sexual Dimorphism in Swallowtails

Black swallowtails (Papilio polyxenes) are known for their sexual dimorphism, meaning that males and females have different physical characteristics.

For instance, male black swallowtails usually have a more vibrant and distinctive pattern on their hind wings, while females tend to exhibit less colorful markings.

Pair of Black Swallowtails (female on left)

In your encounters with these butterflies, you might notice the following differences between male and female black swallowtails:

  • Males:
    • Brighter yellow spots on their wings
    • Often a more striking overall appearance
  • Females:
    • More brownish in color
    • Less prominent yellow markings

Notable Markings

Several markings on black swallowtail butterflies can help you identify these beautiful insects. Some notable features include the presence of yellow-orange dots and transverse bands on these butterflies.

Here are some markings you might see on black swallowtails:

  • Hind wings: The presence of two rows of red-orange spots, which can help differentiate black swallowtails from pipevine or dark female eastern tiger swallowtails. Hind wings also have a small spot just to the basal side of the median row.

  • Yellow spots: Yellow spots near their hind wings can also help you recognize black swallowtails. Males have more prominent yellow spots, while females have less noticeable markings.

In summary, when identifying black swallowtails, look for their unique yellow-orange markings and take note of the differences between male and female butterflies.

Keeping these details in mind will make it easier for you to spot and recognize black swallowtails in the wild!

Human Interaction with Black Swallowtails

You may encounter black swallowtail caterpillars in your garden or at the nursery.

These caterpillars are usually found feeding on a variety of host plants, such as milkweed, thistle, and magnolia. They are not considered harmful pests, but their presence might still surprise you.

A common way to protect black swallowtail caterpillars from predators is by using mesh netting.

Mesh provides a barrier against birds and other insects while still allowing air circulation and sunlight access.

When placing mesh, make sure it covers the entire plant, including any surrounding shrubs where the caterpillars may seek refuge.

Black swallowtails are known to feed on various plants which can be found around your house:

  • Milkweed
  • Thistle
  • Olive
  • Magnolia

Here’s a comparison of some plants and their significance for black swallowtail caterpillars:

PlantImportance for Caterpillars
MilkweedPrimary host plant
ThistleSecondary host plant
OliveTertiary host plant
MagnoliaPopular host plant

When observing black swallowtails in the wild, you may notice them flying near the ground or roosting on tree branches. It’s essential to be cautious not to disturb their natural habitats or interfere with their life cycle.

Lastly, it is important to stay informed about the signs of black swallowtail caterpillar presence, such as egg clusters or caterpillar frass.

This knowledge will help you in maintaining a healthy environment for these fascinating creatures and contribute to their conservation.


In summary, black swallowtail caterpillars face various natural predators, including wasps, spiders, and ladybugs. These predators are attracted to the caterpillars as a food source.

To defend themselves, black swallowtail caterpillars have evolved mechanisms like the osmeterium, an organ that emits an unpleasant odor to deter predators.

Additionally, their diet of Apiaceae family plants makes them distasteful to many predators.

Understanding these predator-prey dynamics is crucial for those interested in conserving and supporting the population of black swallowtail caterpillars in their natural habitats or gardens.


  1. https://alabama.butterflyatlas.usf.edu/species/details/106/black-swallowtail

  2. https://hort.extension.wisc.edu/articles/black-swallowtail-papilio-polyxenes/

  3. https://mdc.mo.gov/discover-nature/field-guide/black-swallowtail-parsnip-swallowtail

  4. https://uwm.edu/field-station/black-tiger-swallowtails-family-papilionidae/

  5. https://content.ces.ncsu.edu/spicebush-swallowtail

  6. https://mdc.mo.gov/discover-nature/field-guide/black-swallowtail-parsnip-swallowtail

Reader Emails

Over the years, our website, whatsthatbug.com has received hundreds of letters and some interesting images asking us about black swallowtails. Scroll down to have a look at some of them.

Letter 1 – Black Swallowtail Caterpillars

Subject: Black Swallowtail cats – 3 different instars
Location: Naperville, IL
June 28, 2012 12:20 am
Hi Daniel~
My daughter found 5 Black Swallowtail caterpillars (Papilio polyxenes) this morning on some potted curly-leaf parsley. I do believe there are three of the five instars represented: 2nd, 3rd, and 4th, judging by their sizes (approx. 1/4”, 1/2”, 3/4”)and by the photos from bugguide of the various instars. They appear to change dramatically from one stage to the next, unlike my Monarchs, which vary mostly by size. I can’t find much info on the duration of the swallowtail life cycle. In the heat we’re having, my Monarch go from new pupa to butterfly in under a week. All the best to you.
Signature: -Dori Eldridge

Black Swallowtail Caterpillars

Hi Dori,
Thanks to your excellent documentation, our readers can see how the Black Swallowtail Caterpillars transform and change appearance as they grow.

Black Swallowtail Caterpillar, final instar

Your photos are so wonderful we are posting them all.

Black Swallowtail Caterpillar

Letter 2 – Black Swallowtail Caterpillar

Unknown caterpiller with warning stalks?
Location: Harrisburg, PA.
September 28, 2011 7:26 pm
I was wondering if you had an idea as to what this little fellow is. The first photo shows the results of prodding him with a stem to move him into better camera view. The orange stalks appear to be some sort of defensive measure. Could you inform me as to what they actually do? Any help would be appreciated.
Signature: Joseph Grabko

Black Swallowtail Caterpillar

Hi Joseph,
One of your photos shows this early instar Black Swallowtail Caterpillar on an Italian parsley leaf, one of the garden herbs that serves as a host plant for the caterpillar that is often called a Parsley Worm or Carrot Worm.  Fully grown Black Swallowtail Caterpillars have a striking green, black, yellow and white pattern that your individual doesn’t yet possess since it is an earlier instar.  Caterpillars molt five times between the time they hatch from eggs until they metamorphose into a chrysalis, and each of the stages is called an instar.  The orange stalks you mentioned are a scent organ called an osmetriumthat is characteristic of Swallowtail Caterpillars from around the world.  As you indicated, it is a defense measure that will dissuade predators like birds.  Your individual is one of the earliest instar images we have received of a Swallowtail Caterpillar displaying its osmetrium.

Black Swallowtail Caterpillar displaying Osmetrium

Letter 3 – Black Swallowtail Caterpillars

Help – they are eating my herbs!
Hello Mr. Bugman;
I have thoroughly enjoyed your website; it is entertaining as well as educational. I’ve discovered it this summer and can’t wait to tell our biology teacher at school about this great site. I’m sure to be looking over the identification for this caterpillar, so would appreciate your help. These beautiful, however destructive, critters are munching away at my basil and dill. This is my first year with a small herb garden; I had no idea that I would have such hungry visitors! Would you please identify them for me. Thank you very much (sorry the picture is a little fuzzy),
Oneonta , Alabama
( North Alabama )

Hi Sharon,
Thank you for the compliment. You have Black Swallowtail Caterpillars, Papilio asterius. They are called Carrot Worms by some people. They grow into a pretty black butterfly with yellow spots. The caterpillars have the ability to emit two orange horns and a foul odor when provoked. Send us a sharper photo if you can.

Letter 4 – Black Swallowtail Caterpillar and Chrysalis

images of swallotail caterpillars on parsley
Dear Bugman,
just wanted to share a few more images, hope you don’t mind. all these are from last summer (2005). The swallotail caterpillars ravaged my curley parsley. (at one point i counted over 40 caterpillars of various sizes on this one little plant!!) after they were “full” some of them made cacoons on my purple fountain grass. anyway, hope you like the images!!
thanks for letting me share!
karen hackney
wilmington, NC

Hi Karen,
Thank you so much for providing our readers with wonderful photos of the Black Swallowtail Caterpillar and Chrysalis.

Letter 5 – Black Swallowtail Caterpillar with Osmetrium

Black Swallowtail Caterpiller – with “horns” out
Thought you might like to add this shot. Taken in September in the Dallas, Texas area, near some parsley plants.
Jeffrey L. Cox

Hi Jeffrey,
Thanks for sending us your wonderful photograph of a Black Swallowtail Caterpillar with its Osmetrium or scent gland extended.

Letter 6 – Black Swallowtail Caterpillar, early instar

Early instar of swallowtail?
Hello –
I love your site – I am amazed at what people will put in their hands. Anyway, I have been using the fab book Caterpillars of Eastern North America to try and identify some caterpillars in my veggie garden in Southern New Jersey but think I have become a bit to eagle eyed as they are all very small and none of them seem to be in the book! I think I am not versed enough in the various instars and color variations that caterpillars can come in. This is the most recent caterpillar my husband and I have found. She was on a dill plant that is smooshed between tomato plants. She appeared on June 25 in the evening. Only about 1/2″ long. The white bands in the middle are really throwing me. Who is she? Any help would be appreciated. Thanks!
Jessica Ferguson
Woodbury, NJ

Hi Jessica,
Caterpillars undergo five instars, each followed by a molt. The fifth molt results in the chrysalis stage. Each of the five caterpillar instars results in a larger size, and in some species, a radically different appearance. This early Black Swallowtail instar looks nothing like the fifth instar caterpillar with the distinctive black and green stripes and yellow spots.

Letter 7 – Black Swallowtail Caterpillar

Subject: What kind of caterpiller is this?
Location: Clearfield County PA
September 4, 2012 10:10 am
We were recently at a family get together in PA (near the DuBois area) and we found this caterpiller crawling on te picnic table. My son wanted to keep it and look it up when we got home to see what kind it was. (A few years ago we had found what turned out to be a polyphemus moth when it was a caterpiller & it spun it’s home over night so we found out how to care for it until it emerged the following spring. Quite a nice way to learn & observe 1st hand.). Have you any idea what this caterpiller will turn out to be since it has also spun it’s home already?
Signature: Curious in Ohio

Black Swallowtail Caterpillar

Dear Curious in Ohio,
This is the caterpillar of a Black Swallowtail, a lovely, large butterfly with black wings and numerous spots and markings.  For the record, Black Swallowtails do not spin a cocoon.  The caterpillar will spin a silken girdle to support the chrysalis in an upright position, but the chrysalis is otherwise bare.

Thank you so much.  Can you tell me if there is anythign specific we should do to make sure it is well through the chrysalis stage?  Also – when will it emerge?  Thanks!

Ensure it is not too dry nor too damp.  Give it fresh air.  We suspect it will remain in the chrysalis for several weeks.  We found a wonderful page on Joyful Butterfly that should answer all your questions.

Letter 8 – Black Swallowtail Caterpillar

Subject: Bright green caterpillar
Location: Central Ohio
August 20, 2013 5:00 pm
This Caterpillar was on my parsley plant in mid August in central Ohio.
Signature: Mark D.

Black Swallowtail Caterpillar
Black Swallowtail Caterpillar

Hi Mark,
This is the caterpillar of a Black Swallowtail, and it is sometimes called a Parsley Worm or Carrot Worm.  The adult Black Swallowtails are lovely butterflies.

Letter 9 – Black Swallowtail Caterpillar

Subject: Striped caterpillar
Location: Prince Edward County, Ontario, Canada
August 26, 2015 6:11 am
Any clue as to what this is going to turn into?
Signature: Susan

Black Swallowtail Caterpillar
Black Swallowtail Caterpillar

Dear Susan,
This is a Black Swallowtail Caterpillar, and we suspect that parsley, carrots or some other related plant was found in the immediate vicinity of the sighting.

Many thanks – what wonderful service.  I’m so glad I moved the caterpillar out of harm’s way!  We have lots of Queen Anne’s Lace nearby….
Goddess of Chuckery Hill

Letter 10 – Black Swallowtail Caterpillar

Subject: Black Swallowtail caterpillar
Location: ohio
September 16, 2015 5:10 pm
I looked this one up, to see if it was a monarch, and am 99% sure this is a black swallowtail caterpillar eating my carrots. The carrots are almost ready to harvest, so they’re welcome to the leaves, but where will they chrysalis/metamorph? I don’t want to take away their environment. We have flowers nearby, xenias, etc. that all the butterflies have been going nuts over, will they go there?
Signature: Amber

Black Swallowtail Caterpillar
Black Swallowtail Caterpillar

Dear Amber,
The Black Swallowtail Caterpillar is sometimes called a Carrot Worm or a Parsley Worm.  It will likely try to find a protected location to metamorphose into a chrysalis as it will most likely pass the winter in the pupal form.


  • Bugman

    Bugman aka Daniel Marlos has been identifying bugs since 1999. whatsthatbug.com is his passion project and it has helped millions of readers identify the bug that has been bugging them for over two decades. You can reach out to him through our Contact Page.

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    Piyushi is a nature lover, blogger and traveler at heart. She lives in beautiful Canada with her family. Piyushi is an animal lover and loves to write about all creatures.

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18 thoughts on “What Eats Black Swallowtail Caterpillars: Meet Their Predators”

  1. I think I saw one of these guys in my garden today. He was quite small, about a centimetre long, and the white band and orange spikes were not well defined. But I’ve seen black swallowtail butterflies in the garden this summer, and the caterpillar was on (of course) the parsley that I picked for dinner. Don’t worry, he didn’t end up in the potato salad, I threw him into the peonies on his piece of parsley.

  2. I realized that too late. I’d forgotten, and was reminded while reading about swallowtails, about how specific their dietary requirements can be.

    This morning I found a caterpillar on the parsley that might be the prepupal phase of the black swallowtail. I have to do some more research and observe it a bit more closely. It’s much larger than the first one. I mistook it for a monarch caterpillar, but of course those don’t eat parsley either. It has black and green stripes, and I can see remnants of the little orange spikes on the black parts. If I can find my camera battery (we’ve just moved) I’ll take a picture and submit it.

  3. Hi Daniel! Thank you for your kind words. Just one thing: the middle photo caption reads “final instar”. This can’t be correct because the caterpillars have molted at least once more since that stage. They’re now (for comparison) about the size of a 5th instar Monarch. They’re striped with lime green, white and black with orange spots, and they longer have those spiky tufts. I know nothing about the Black Swallowtail life cycle, but my guess is they’re readying to pupate. All the best, and Happy Fourth to you! -Dori

  4. As fascinating as parasitoids might be, I am happy to state that I have yet to experience them firsthand, other than on tobacco hornworms. The mesh screens on my Monarch (and now Swallowtail) boxes is too fine to allow flies and wasps in, and although I have had more cases of Monarch caterpillar death-by-NPV this year, I have never had the pleasure of witnessing fly or wasp pupae emerge from a butterfly chrysalis. By the way, I saw a Black Swallowtail buzzing my potted curly parsley this morning, and after she left, I found four eggs thereupon. This will be my very first experience with Swallowtail hatchlings. They do seem to take things far more slowly than the Monarchs.

  5. Even though it is still early September, I am not entirely sure that Curious’s PA pupa will eclose in a few weeks. In my experience in Illinois, Eastern Swallowtail caterpillars that pupate in late summer overwinter as such and will not emerge until late May or early June the following year. In that case, I leave my pupae outside in a wooden box with a mesh “door” for fresh air, as you suggest. Even in the harshest winters, full of snow and below-freezing temperatures, healthy adult butterflies emerge in the spring. Despite being tempted to bring the pupae inside during extreme cold snaps, I don’t; the last thing I would want is for a butterfly to emerge in my garage or basement in the middle of winter with no chance of surviving outside. It might be the weather that decides, and the best course might be to check it daily. All the best!

    • Thanks so much. We were trying to find information on the hibernating stage of the Black Swallowtail. We suspected it to be the chrysalis, but we didn’t want to rule out eggs, though if eggs overwintered, the plants upon which they were laid might not overwinter. We know that parsley overwinters quite well.

  6. I found these all over my parsley in Kissimmee, FL. Did not know if they were friend or foe. Looking forward to seeing which Swallowtail I have. How much parsley do they eat?

    • If the caterpillars are eating parsley, they are Black Swallowtails. Males and females exhibit sexual dimorphism. If they have blue markings on the hind wings, they are females. Males have more pronounced yellow spots and lack the blue markings.

  7. I live in central Minnesota and grow carrots every year.( I have lots of monarchs) I have never seen a Black Swallow tail butterfly or catrpillar before. My 6 year old daughter and I were looking at the carrots today when we spotted at least 8 Black Swallow tail caterpillars. Can the pupas survive our -20 degree temperatures?

  8. What do they look for when they are ready to pupate? I move monarch pupas all the time so we can watch them hatch in the house. I suppose I could do the same thing in my 30 degree garage.
    What is the normal pupation time for this swallow tail.


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