No, that is not a Monarch caterpillar on your parsley plant.

I am often asked “why is that green, yellow, and black Monarch caterpillar eating my parsley”?

Eastern Black Swallowtail Butterfly caterpillarBlack Swallowtail Caterpillar

Chances are, you will never see a Monarch caterpillar on your parsley. By far and away it is more likely that you have the caterpillar of the gorgeous Black Swallowtail Butterfly (Papilio polyxenes).

Caterpillars that are actively feeding are usually only found on their larval host plant(s), the plant they have developed a distinctive coevolutionary relationship with over millennia. Monarch caterpillars do not eat parsley and Black Swallowtail caterpillars do not eat milkweed, and if either attempted, they would not survive. Black Swallowtails were in the past commonly referred to as the Parsnip Swallowtail as their caterpillar food plants belong to members of the Umbelliferae, or Carrot Family. The diet  of the Black Swallowtail caterpillar includes the foliage and flowers of carrot plants, fennel, dill, parsley, Queen Anne’s lace, and parsnips.

Monarch CaterpillarMonarch Caterpillars

The Monarch caterpillar is yellow, black, and white. The Black Swallowtail caterpillar is green, black, and yellow.

Please see my Life Story of the Black Swallowtail Butterfly film’s website for videos and more photos documenting the butterfly’s life cycle.

Eastern Black Swallowtail Butterfly caterpillarMetamorphosing from this

to this…

Eastern Black Swallowtail ButterflyBlack Swallowtail Butterfly (Papilio polyxenes)

See Life Story of the Black Swallowtail Butterfly film website for videos and more photos documenting the butterfly’s life cycle.

73 thoughts on “No, that is not a Monarch caterpillar on your parsley plant.

  1. Jan Oldenburg

    I was washing some parsley sprigs in the sink last week and found a chrysalis hanging from the stem. Thought for sure it was a monarch! Since I’ve found a few caterpillars and more chrysalises on what was left of the parsley plants. I brought them all inside. Two caterpillars are still ravenous but the parsley is all gone! Hoping their instinct will make them form chrysalises since the food is gone!

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  2. Kim Smith Post author

    Dear Jan,

    You need to go to the store immediately and purchase parsley or fennel as the caterpillars sound like they are still in the feeding stage. They need to reach maturity to become a chrysalis and will die if they do not have food. Wash the parsley and place the stems in a container with water. Gentyl transfer the caterpillars to the food plant (a soft, smallish watercolor brush is ideal for moving caterpillars).

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    1. Nadine

      I have these on my carrot plants. Is it safe to eat the carrots? How long will they stay? I’m wondering when I can harvest my carrots without disturbing the caterpillars.

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  3. Jan Oldenburg

    Thanks Kim! I think we’re doing OK. The last 2 babies are slowing down. They had been stripping the parsley stems and the plant has new foliage which I’m snipping off as soon as I see the leaves! But it seems the 2 are gearing up to morph soon. I’ve raised Great and Black Swallowtails, taking them in when the heat and drought get bad here in FL. I release them near our butterfly weed bushes and have a pan of wet sand to keep them hydrated. Love your site, Kim!

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  4. Deanna Russell

    Found this little guy today acting a tad sluggish on a parsley stem. Cut the stem back and placed it with the caterpillar on a nearby compost pile (nope, I did not hurt the caterpillar!) Googled ‘black & yellow caterpillar’ and found your wonderful and informative blog! 5 minutes ago I crept out in the dark with my flashlight and found the little guy in the same place. I put him back near my parsley in my raised bed, still holding onto dear life to that stem! I figure I’d rather have the Black Swallowtail than the parsley. I hope he makes it! Thanks again!

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  5. Sondra Edwards

    I grow parsley to feed my pet bunnies, so I need the parsley. Will leaving them on the plants destroy the foliage? What should I do? i want the parsley yet don’t want to harm the caterpillars. Please help!

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  6. Martha Brettschneider

    I just found two of them on my dill plant. Beautiful! I don’t care if they eat the whole thing — I never get in the way of transformation. Also just searched “green black yellow caterpillar” and came up with your post! Yay! Always looking for other garden bloggers. Thank you!

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    1. Kim Smith Post author

      The eggs look like little tiny golden yellow dots, no larger then the size of a pin head. See my Black Swallowtail film website and trailer for more images.

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  7. Sue

    Our Black Swallowtail caterpillars must be ravenous as they demolish our parsley and dill, no matter how much we plant. At least now I know to let them be.

    Thanks for your informative sight!

    Sue

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  8. Amy

    I am feeling terribly guilty now! I found two of these beauties and thought for sure they were pests. I immediately trimmed the leaf off (they were on my carrots) and tossed it. After I read this I ran out (literally 5 mins later) and tried to retrieve them. I found one still perfectly on the plant. I placed back in the garden. I have searched my yard for the other leaf. The only thing i can think is a bird swooped down and took off with it. 😦

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    1. Kim Smith Post author

      Good news Amy–so glad you found the caterpillars!!! Birds do sometimes eat them and recently I had a wasp bore into a chrysalis and deposit her eggs. It’s not easy being a caterpillar!

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      1. Amy

        Is it possible to contain and hatch indoors, or is that cruel? I worry that I made them susceptible to things now that I tampered with their home.

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  9. Maureen

    I have parsley planted in a hanging basket. It was a good sized plant yesterday, but this morning there are at least 20 caterpillars on it and almost all the foliage is gone. They are hanging onto bare stems. Some of these guys are a good size, others are really small. My questions are, how long do they feed…a week, two weeks? This might get expensive if they keep hatching. Where will they form their chrysalis, on these bare stems or will they crawl to neighboring plants/bushes?

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    1. LOUISE A. MOYER

      \LOUISE PA.SEPT4 I HAVE5 SALLOWTAIL ON MY PARSLEY AND SMALL LITTLE BLACK ONES. WHAT A JOY TO CHECK THEM EVERY DAY. WHEN WILL THEY GO INTO THE COCOON, AND WILL THEY BE OK IF THE WEATHER BECOMES COLDER. REPLY THANKS

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  10. Kim Smith Post author

    Wow–wonderful that you have so both have so many caterpillars!!!

    The caterpillars feed for abut ten days. In my experience, they switch readily from parsley, to carrot tops, to fennel, dill, and parsnips. They feed for about 2 weeks.The caterpillars typically wander away for the plant when they are ready to pupate and will look for a sturdy twig, stem, or even a fence post, or eave of your home. I even had one pupate on the thin edge of an envelope. At this time of year, the caterpillar will pupate, and then may remain as a chrysalis the entire winter.

    I wish my Black Swallowtail film was available today, because I know it would be so helpful. I’ll keep you informed as to when copies will be available for sale.

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  11. Maureen

    All of my caterpillars have now flown the coop, or more accurately the parsley. I know where 2 of them are: one attached himself to the siding of the house, formed a chrysalis, and now I wait to see if/when he emerges. The other, sadly, attached himself to a nicely hidden stem on a neighboring plant and within a day was dead. Strange. He appeared healthy, good sized, and left the parsley of his own volition so his death was both surprising and mysterious. I hope the other 18 (or so) had better luck.

    I did buy additional parsley because they ate every leaf of my plant, and as you recommended washed it thoroughly…they ate all that, too. It’s been an interesting week.

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  12. Debra

    Hello.. I went out side to snip some parsley.. I must have 20 of these on my plant.. it is September here… whats going on, will they die because of the season… I still sniped some.. If washed can I still eat my herb.. :0)

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  13. Maggie

    Hi there, I am so glad I found your post – I was just googling – “what is a monarch caterpillar doing on my parsley?” – when I realized that they are a little different looking. I was sure it was a beautiful species though – and it is.

    I am worried though – it’s still warm here in Winnipeg, but it’s almost the middle of Sept. and the nights are getting down to around 10C, and the leaves are falling – will the 2 full grown fatties on my parsley survive to pupation and immerge in time to flee the cold?

    The parsley is on my patio table in a herb pot – not in the ground – does that matter?

    I want them to live – they can have all the parsley they want …. 🙂

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  14. Linda Sydell

    The weather is getting cool here. When will my butterfly hatch. I have taken the caterpillar to my classroom. He is still eating parsley. What if it is too cold to release him outside?

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    1. Kim Smith Post author

      Hi Maggie and Linda,

      No it does not matter whether the herb is in the ground or in pot.

      As far as being too cool–

      The caterpillars will pupate, and if they don’t emerge, will spend the winter in their chrysalis form, and then emerge perfectly next spring. I have a chrysalis on a potted fennel plant that pupated many weeks ago, along with half a dozens other caterpillars. All the rest emerged, except this one. If it has not emerged by winter, I will leave the chrysalis on the plant and place in a terrarium on my unheated porch, out of direct sunlight. This way the the chrysalis will experience normal outside temperatures and won’t emerge in the dead of winter.

      I think you’ll be interested in seeing my Black Swallowtail film, which I will have copies for sale by the holidays.

      http://butterflyfilm.wordpress.com/

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  15. Karen

    I always say “every day is school”, and today was no exception! I found a beautiful caterpillar on my parsley plant today and moved him over to a hanging basket. When I googled a descripition of the gorgeous striped fellow, and learned he needed to eat parsely to survive, I moved him right back. Just went to check on him and he’s eating away, none the worse for his temporary relocation. Thanks, Kim, for sharing your knowledge with the rest of us.

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  16. Katharine

    Hello! We’ve had one of these little guys on our carrot plant for the last month or so. All he’s done is get bigger, but he hasn’t done much else. It’s getting VERY cold here (November in Minnesota) and, even though I have a frost blanket over the little garden bed he’s made home, I’m still very worried about him. So today I brought him in and made a little terrarium from an old plastic container. I poked holes in it and stuck a bunch of carrot tops and parsley inside (and onion stems, since he seems to like climbing on them). is this the right thing to do? Will he pupate overwinter if I leave him in a dim, lukewarm spot? Will I need a larger container?

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  18. sam

    I found one on my dill, didn’t know what it was, clip some dill with it on and put it in a jar, to identifiy it. Forgot it until the next day, found it on your website. I put it back on some dill that is leaning on some parsley. It can eat all the dill, parsley, whatever it wants!

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  20. Michele Carsrud

    Thanks for this post. I’ve had caterpillars in my parsley, but didn’t know until now what species they were.

    This is the third year I’ve planted parsley, but for some reason, I haven’t seen caterpillars this year. Any idea why? (I hope I didn’t accidentally destroy eggs when I harvested parsley.)

    To identify the species, I used a photo that I took on September 11th of last year. On October 5th I took photos of a pretty butterfly I saw hanging around my garden. I had no idea until I found this post today that the butterfly was the same species as my parsley caterpillars!

    Like one of the other posters, I grow parsley to feed pet bunnies. But, once the caterpillars show up, I leave the parsley for them and just buy parsley for my rabbits.

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  21. Kathleen Hoffer

    Thank you! I did have these confused with monarch larvae. I even pulled up a milkweed plant from a nearby yard (sorry, neighbor!) just in case. So glad for the internet.

    I have 5 on my two dill plants. I was worried they’d run out of food before they were ready to pupate, but a nice woman from the University of Minnesota entomology department assured me they’d be fine. Go little guys, eat away! I can always buy more dill from the farmer’s market.

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  22. Wendy

    I have the Blacktail swallow catipillars in my back yard but do not have them in my garden but amongst the weeds(I believe is Queen Anne’s Lace). I too thought they might have been Monarch butterflies, and looked them up to find out.
    By the way I loved the video of the stages.

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  23. Phillip

    I just found three of these guys eating parsley in a potted plant. They’ve almost eaten it all. I read some of the comments above that recommend getting more parsley, but I wasn’t sure if they meant a new parsley plant or cut parsley from the grocery store. Is there anything else I need to do to help these three along?

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    1. Kim Smith Post author

      Hi Philip, a new parsley plant would be best however, as long as the leaves are fresh and green, cut parsley is fine, too. They will also eat dill, fennel, and carrot tops.

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  24. Beryl Morgan

    Just found your site and want to say thank you. My son and I found about 4 on a parsley plant on our patio. Found 3 more (2 on screen door one in rose bush), so we helped them move to the parsley with their friends! We homeschool so this was a fabulous, “surprise” lesson. We took many photos and will take more as the days go by. They have eaten most of the parsley plant. I wanted to add some dill as you suggested…all I had handy was some cut dill that I had frozen whole stems. We put that in the pot and they seemed to like it. Thought we would add some cut parsley later today. Did we do ok? Should we bring them indoors?

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  25. BJ

    I just found a Black Swallowtail on my carrot tops. Wasn’t sure if he was poisonous to humans (is he??) and he’s a threat to my carrots (still growing) – doesn’t appear to be so we’re just going to leave him alone. Very pretty but I’m not touching him!!

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  26. Creatively Motivated

    I came home and found these 2 to 3 of these pests on my dill (or what was left of it) and frantically removed the entire stem from the plant and trashed it. Thoroughly disgusted, yet curious, I decided to find out what it was that was taking food from me. I arrived here, read all of the comments, then ran back outside to retrieve the cutting. I placed it in a separate pot where I have more dill growing and I kind of hope they make it now! They still gross me out, but I’m kind of amazed at their process at the same time.

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  27. lb

    Is there something we can put near the plant that they might attach to form their chrysalis?
    I am hoping to continue to watch as they morph. We are in the middle of the city and surprised this is happening at all on our little Parsley plant!

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  28. Christine Lemieux

    I loved your video of the stages. There are a number of caterpillars on our parsley and dill and we were thrilled to find out what they are. I have seen some of the butterflies in the garden and hope these guys make it as well! I will be looking for chrysalis (s)! Many years ago I “disposed” of a number of caterpillars I found on a Joe Pye Weed plant. I feel very guilty now and will never do something like that again. Sites like yours provide the education that is needed. Thank you.

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    1. Kim Smith Post author

      Thank you for writing Christine. Yes, I did the same when I was a beginning gardener and destroyed the chrysalis of a Spicebush Swallowtail on my spicebush plant; as guilty as we feel, we learn from our mistakes.

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  29. Shannon

    Hi!

    I had a pretty big one on my parsley plant this morning (it had been there about a week). But, I can’t find it now. Any idea where it could have gone? I imagine they don’t move that fast.

    Thanks!
    Shannon

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    1. Kim Smith Post author

      But they can cover a great deal of ground. When they are ready to pupate caterpillars oftentimes move off the plant and will pupate on a sturdy twig or even a house eve or underneath a porch railing–really anywhere that feels solid to them.

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  30. Amber

    I have to young boys ages 5 and 3. We have an herb box that we started from seeds and put on the front porch through the spring and summer. recently we found about 5 of these guys hanging out on our parsley. Decided to bring one in and do some research to see what he was going to be. The boys are so excited to see what “Willbur” (yes he had to have a name) is going to be. He is getting VERY big and slowing down some. hoping he will change soon. Thanks for all of the wonderful information.

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  31. Kim Smith Post author

    Amber , do you have a terrarium with a mesh lid? Wilbur will probably move off the plant and pupate where you can’t see him. If you cut the stem of the plant and place it the terrarium, your kids can watch metamorphosis unfold.

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  32. Nan

    I put the potted parsley plant in a fish tank with a screen lid. There are about 8 to 10 caterpillars currently on the plant and there seem to be more everyday. Is there anything else I can do to insure they are healthy. Temps are about 75 degrees here on long island currently. I will leave the terrarium outside on a covered porch. Thank you.

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    1. Kim Smith Post author

      Sounds great Nan. Just make sure they have plenty of fresh food. You may want to add several sticks placed upright so that when they are ready to pupate they will find a sturdy spot.

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  33. Heidi

    Hi Kim! Great info, thank you! I also found a caterpillar on parsley plant when was bringing in for winter but put it back outside, was like a week ago & it’s still there, just hanging out on one of the branches (or whatever u call, stem maybe) hasn’t really eatten much & not moving around much.. It’s starting to get really cold here, in Michigan & Thu night will b below 32°F. The snow will get really deep, way deeper than pot etc. What should I do? I could move it to a enclosed porch type area at back of house but it will freeze, bottles of water freeze solid after awhile…I know some types of caterpillars have like an antifreeze but don’t know about this.. Also it doesn’t look much like pics of swallowtail but it is black w yellow dots (not raised) & whitish dots on feet. Pic have isn’t very good but could send…any idea on what I should do is greatly appreciated! Thank you!

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    1. Christine

      I would like to know the answer to this question as I too have a caterpillar on my balcony herb garden. It’s July here (Toronto, ON) so still hot but will get cold in Sept. Oct.

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      1. Kim Smith Post author

        Hi Christine, at this time of year the caterpillar will grow really fast, pupate, become a chrysalis, and emerge as an adult butterfly before the summer is out.

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      2. Christine

        Oh, I feel so awful about this. I left it there and went to work, looking up the info, and when I got home moved it to a bigger parsley plant. Went to look for it later and it was gone! I looked all over the balcony and realized that my cat must have got to it. I just feel so bad for the way it died. Didn’t even think the cat would bother with it. I missed an amazing thing but I can’t really be angry at my cat – she was just going by her natural instincts – I am angry with myself for being so stupid. 😦

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    2. Kim Smith Post author

      So sorry I never saw your comment in time. The caterpillar most likely pupated and became a chrysalis. Black Swallowtails winter over in their chrysalis form, emerging in the spring, around the time of year the lilacs are blooming. In response to Heidi.

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  34. Kim Smith Post author

    To Christine. Most likely a bird ate it and that’s just what happens. Birds lover caterpillars. We keep all our caterpillars in a terrarium, with a screen on top to keep out the birds. They have a much better rate of survival in a terrarium than in their natural environment 🙂

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    1. Christine

      Actually, my balcony is netted in (to keep pigeons off of it) so it wouldn’t be a bird. Pretty sure it was my not so darling little cat.

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  35. Jackie

    We are raising both swallowtails and monarchs and we have a monarch that is DEFINITELY eating the parsley. I’d be happy to post a video–I’ve never seen anything like it!

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  39. Thom Lofquist

    Hi Kim, Thank-you so much for your very informative Blog.
    We are in Minnesota and had a very large pot of parsley with a dozen or more caterpillars we thought were Monarchs we first noticed in September. Glad to have found out they are Black Swallowtails from you.
    As the weather has cooled I first very carefully took the pot into a shed and now I have moved it inside the house. The last caterpillar has now gone to the Chrysalis stage just yesterday. Obviously, its getting colder outside here in Minnesota. Sometimes the night time temperatures are dipping into the 30’s with some daytime temps only in the 50’s. Not really butterfly weather anymore.
    Would you advise simply putting the pot with the chrysalis’s back into the shed where they will eventually feel the full cold of winter without the wind, etc?
    If any should emerge as butterflies yet this Autumn, it will be pretty darn chilly in all likelihood. Do you have any suggestions as to what we should do if that happens?
    We wondered if there was a gentle and clever way to ship them further south, or is a road trip in order?
    Thanks!
    Thom

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    1. Kim Smith Post author

      Hi Thom,
      Thank you for writing. Yes that is exactly what I would do, put the chrysalides in a place where they will experience your region’s winter. We keep our Black Swallowtail pupa (and all cocoons) on our open, exposed front porch. I am afraid if we left ours in a shed, we would forget about it by the time it is ready to emerge. The BlSw chrysalides that form at this time of year will emerge next spring; ours usually do at about the same time the lilacs are in bloom. We don’t want to ship them out of town–you have next year’s generation:) In the unlikely case the adult butterfly emerges, place it on a nectar plant if any are still flowering, but with your reported chilly night temperatures, i doubt this will happen. Best wishes and send us a photo next spring if you would like:)

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  40. Sarah Kline

    ROF LOL!!! We were just wondering what that Monarch caterpillar was doing on my mom’s parsley plant, and then found your post! You perfectly answered our questions. Thank you so much for the detailed photographs and information!

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