these monarch caterpillars failed to pupate (turn into a chrysalis)...
why? what happened to these caterpillars?

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see also:
raising Monarch caterpillars in Santa Barbara
image gallery of milkweed, Monarch caterpillars, butterflies, etc
Monarch caterpillars eat butternut squash
tachinid flies are killing my monarch caterpillars!

As part of my study on tachinid flies killing Monarch caterpillars, I attempted to "raise" several Monarch caterpillars from eggs. The first egg I raised was a success. The caterpillar hatched, grew up into a big fat healthy caterpillar, then pupated and turned into an elegant light green chrysalis, and then later emerged transformed as a healthy happy Monarch butterfly. I expected the same success with two subsequent eggs I collected just after observing a butterfly lay them, but the results were quite different. For egg #2 and egg #3, the caterpillars hatched as expected. The two caterpillars seemed fine and grew to full-size, and I expected them to turn into chrysalises just like the first caterpillar. But instead, both failed to successfully turn into chrysalises. The caterpillar from egg #2 started to split its skin, but then stopped, and eventually died. In addition, it wasn't able to hang onto its silk button. The caterpillar from egg #3 sort of turned into a partial chrysalis, but was hanging by its elongated stretched skin, and wasn't a full chrysalis. It too then died. I have not idea what happened to these two caterpillars. It had nothing to do with Tachinid flies, as no Tachinid maggots ever emerged. Instead the to partial chrysalises just darkened over time and then began to mold.

monarch caterpiller fails to turn into a chrysalis  deformed monarch chrysalis hanging by stretched caterpiller skin

So if anyone know what could explain the two pictures above, please comment and let me know. Why is the caterpillar from egg two not hanging directly from his silk button, and why did he start to split his skin and then stop. And why is the chrysalis from egg #3 caterpillar deformed, and hanging from the elongated caterpillar skin. I've never seen anything like this before.

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Comments / Questions / Feedback:

Comment by Mary on Wednesday, July 27, 2016
This is very interesting. Has me stumped too. I just thought it is interesting #3 still has its caterpillar prolegs even after becoming a pupa. Or rather the abdomen still looks like the caterpillar's.
I wonder if anyone else was able to help you figure out what happened. Doesn't look quite like the OE disease monarchs get? Could the food you gave them have been exposed to pesticides? (nursery bought plants or harvested from a park, business or wherever else they might use chemicals on their lawn and garden?)) How was the humidity and temperature? Did they have trouble spinning their silk pads? I notice if they don't get a decent anchor or have to redo it, sometimes the caterpillar might not make it in time to properly J before having to split. Another thing that can do harm is if they get an injury on their rear end.
As far as #2. The caterpillar probably stopped because it was too weak to achieve the molt. Another culprit could be the dreaded NPV virus. This would cause them to turn into liquid goo.

Reply by Steve (Cranial Borborygmus)
Hi Mary, Thanks for your comment and thoughts. My backyard is pesticide free, and all of my milkweed was grown from seed, so I don't think it has anything to do with pesticides. It might be a virus like you've suggested, but if so, it was a one-time thing. I've never seen anything like this before, and never since. I let most of the caterpillars grow up on the milkweed, and then they disappear and turn into chrysalises somewhere (I hope). Sometimes I find chrysalises (or empty chrysalises), but often I don't. So maybe it's happening in "the wild" of my backyard, but I'm not aware of it. I still lose a lot of caterpillars and chrysalises to the Tachinid fly, but again, I've never seen something like this again. If anyone else has any ideas, please let me know. Thanks again for your comment!

Comment by Monique on Sunday, August 28, 2016
Caterpillars are easily stressed if it looks like the food supply is low or if they "run out" often and they will begin to pupate prematurely (before they really should - sometimes as early as 4th instars). #3 may have died halfway into pupation. I have seen some remnants of prolegs on chrysalis and believe it is due to a hasty pupation (less than 18 hours in the J mode). I believe #2 probably also pupated before full maturity as well. It is also important to have a proper anchor so the contractions can pull the skin off the body quickly with exhausting the caterpillar. Can't really see what is happening on egg #2 where it is anchored. A sign of being too weak to pupate is being too weak to form a proper silk pad to anchor to. I think the caterpillar needs copious amounts of food with no interruptions for as long as possible as a 5th instar before pupating to maximize success.

Reply by Steve (Cranial Borborygmus)
Hi Monique, As far as I remember, the caterpillars had enough fresh milkweed leaves, but maybe the issue was still some kind of stress as you suggest, and they simply began to pupate before they were ready. I'm just surprised I've never seen this before (and I did have some caterpillars run out of milkweed and I then fed them butternut squash, and they lived and turned into butterflies), and I've never seen it since. It also happened to two in a row, not just one. Anyway, your explanation could be it, at least that it was some form of stress, but not necessarily running out of food. Thanks for your comment and insight!

Comment by Monique on Wednesday, August 31, 2016
Depending on how the milkweed is presented they may not migrate to the fresh leaves and cling to their old stripped down stems (check the amount they are eating from the leaves). Excessive heat or dryness will make them pupate prematurely and usually unsuccessfully. Make sure their environment is humid >50% Relative Humidity, and stays below 81F and does not fluctuate more than 15F (glass enclosures like an aquarium can get very much hotter than the surrounding air even if not in direct sunlight). Also pulling cats from the "wild" at too late a stage and bringing them into captivity will make them pupate. They just want to get out of the captive environment and will not eat anything. They have a healthy flight instinct (fight or flight) and if they are scared they can be in flight mode for hours until they are exhausted and pupate. Stress really takes a toll on them. Maybe #2 attempted to pupate in direct sunlight. Make sure they are not pupating in direct sunlight and relative humidity is extra high for safety.

Reply by Steve (Cranial Borborygmus)
Hi Monique, Thanks for your additional comment and great information and advice. In my case, these two caterpillars were raised from eggs I found outside. Their little shelters were outside in the shade with ample airflow, and they had plenty of fresh milkweed. I would add new leaves and they finished the old leaves, and they would quickly move over and start eating the new leaves. I don't remember what the weather was like, since it was last summer. It might have been hot and/or dry. I just can't remember. In any event, your information is great advice for anyone raising caterpillars in captivity. Thank you!

Comment by Pam on Tuesday, September 20, 2016
I don't have any ideas regarding your issue but this year I have had the same problem. I have had several cats go into J shape and only form 1/4" chrysalis. Some were hatched from eggs and others I found as 1st or 2nd instars outside. Raised them indoors in a spare bedroom. None ever ran out of leaves and I don't touch them. I'd like to know what's going on.

Reply by Steve (Cranial Borborygmus)
Hi Pam, I'm sorry to hear that you had the same or similar problem. Very strange. Thanks for sharing your experience.

Comment by Linda McCulloch on Saturday, September 24, 2016
Hi all, I was extremely happy this month to have a lot more monarchs, and therefore many more cats on my milkweed. Like many of you, my yard is pesticide-free, and all the milkweed is self-seeding and has been for several years. I have plenty of milkweed so no worries about the cats running out of food. So at least 9 of the cats got really big, fat, healthy-looking etc. This week they began working their ways off of the milkweed and over to other plants to pupate. (They seem to really like to pupate on our large clumps of garlic chives.)
But! Yesterday and then today I saw two of the cats, hanging from the chive stems, just straight down, with their silk hanging loose. They never formed the J shape, or if they did I did not see it. Now they are sort of shriveled looking and obviously dead.
I have not seen any Tachinid fly maggots (yet). And now that I have decided to look out here on the Internet and have seen some similar problems, I am concerned. We do live in Georgia, which is in an extreme drought situation and it's been hideously hot. Could the cats have gotten dehydrated somehow? I read on another site that some folks think it's a good idea to spray-mist them as they grow.
Any additional thoughts welcome. If you need me to upload a picture let me know. I haven't shot any, but I could do that if it would help.

Reply by Steve (Cranial Borborygmus)
Hi Linda, I'm not sure what you mean when you say the dead caterpillars were just hanging there "with their silk hanging loose". But if you mean you saw thin white silk threads dangling from the dead caterpillar, then that means the cat was killed by the Tachinid fly maggot, and the maggot has already emerged and then dropped to the ground via the silk thread. You probably won't find the maggot because it will wiggle away and hide, and then turn into a hard little reddish-brown "seed". A few days later, the "seed" will hatch and the fly will emerge. I have a different post on this website about the Tachinid fly, and have pictures on it. It's a problem I haven't been able to solve yet, but fortunately at least a few of our caterpillars somehow avoid the flies and turn into butterflies, but with the others it always hurts to lose them.

Comment by Linda McCulloch on Sunday, September 25, 2016
Hi Steve, Thank you so much for your answer, I am now fairly sure that you are correct about the Tachinid fly maggots. Yuck. But your description is very accurate, and the fact that the caterpillars look shriveled and kind of empty would make sense, if the maggot ate them from the inside out. (Double yuck.) I will keep looking for healthy chrysalises of the remaining cats because we had a lot more this year. Fingers crossed.

Comment by Ola on Friday, September 30, 2016
Found this thread because this just now happened to one of mine. Looked healthy, j formed properly, antennae went limp and skin started to split and then stopped. Raised this batch from eggs and cleaned the leaves (though no pesticides used outside) before giving them to caterpillars. First time this has happened to me. Very distressing. Am in So.Cal.

Reply by Steve (Cranial Borborygmus)
Hi Ola, Thanks for your comment, and for letting me know this happened to you too. I think it must be fairly uncommon since I didn't find anything about it when I searched online after it happened to me, but thanks to your comment and also Pam above, I now know I'm not the only one this has ever happened to.

Comment by Debbie on Monday, October 03, 2016
I live in Southern California and this is my first year raising Monarchs. Just recently I had one cat partially pupate, and one hung that it's skin began to shrink from the tail. I'm glad to see other posts with the same experience. I have had successes and losses, losses outnumber successes, unfortunately. I do raise them inside and release them when they are ready. It is October and there seems to be no slowing down of Monarchs laying eggs in my small patch of milkweed! I currently have eight entering into their J stages and have recently released 7. Knowing that only less than 1 in 10 make it into the butterfly stage encourages me for my small hatchery, and very happy for the successes I have.

Comment by Tiffany on Monday, October 10, 2016
This has happened to me with three separate chrysalises this year! It's so strange indeed. Earlier this summer, one of them formed only half of its chrysalis. After a couple weeks of watching and wondering, it was obvious that it was long gone. The next one only formed half, and I figured it would be the same untimely end, but the next day it finished forming the chrysalis! I was shocked! It has only been 5 days since then, so I'm anxious to see if a butterfly will really emerge from that one. And the third just happened yesterday. It looked big and healthy and hung in a J yesterday morning and by evening had only formed a small cap of chrysalis on the top of its head. It's been over 24 hours now and no changes, except it's no longer in a J and is straight and limp. I'm nervous to consider it a goner though since the second one seemed to finish with a little more time. It's just so weird and every failure makes me a little sad, even though we've had over a dozen successes this summer! After reading these posts I'm guessing that they got stressed about the food availability because they were indoors in their own containers but their leaves were on the crunchy side (although the third one did have a butterfly emerge in the same container a couple of weeks ago). It's also pretty dry here in Utah. I'm sure it's too late in the season to find more eggs, but I'm hopeful that this won't happen next year!

Reply by Steve (Cranial Borborygmus)
Hi Tiffany, Thanks for sharing your experience. Maybe this is more common than I thought. It's very interesting that it happened with your caterpillars three times this year. It's especially interesting that the second caterpillar stopped pupating half way through, but then was able to finish pupating the next day. I had no idea that was even possible. I hope you will update us on whether or not that chrysalis turns into a butterfly. This is very strange indeed!

Comment by Sarah on Tuesday, October 11, 2016
I have lots of milkweed around my complex and the yard guys hack the plant so I take caterpillars and sometime cut the chrysalis branch off to help them. I let them roam on my porch with milkweed and other plants available. They can easily crawl to a plethora of moll weed if they want but they stay. They need space. They don't like to be crowded. I supply fresh milkweed flowers on top of having a milkweed plant. This has happened with a few of mine too. I live in Az but keep them in natural environment. Outside. I mist water on the plant sometimes to keep them hydrated and cool too.

Comment by manda on Sunday, November 13, 2016
I am devastated. I had about 10 caterpillars, extremely healthy and the plant was still full of leaves about a week ago. They looked like they were full size, but now I can't find any pupae hanging in the butterfly weed or nearby plants. Do the caterpillars move away.. and if so, why? What do you think happened. I don't even see any dead pupae hanging... basically no trace of them.

Reply by Steve (Cranial Borborygmus)
Hi Manda, Don't be devastated. I think your caterpillars are probably just fine. They won't hang and form a chrysalis when they're in the milkweed. Instead they will wander off somewhere else to form a chrysalis. I think they can go 50 feet to 200 feet or more. All of our outdoor caterpillars get big and then "disappear". We've been luck enough to find a few chrysalises in trees, in bushes, and on walls (up to 50 feet away), and sometimes don't find the chrysalis until later after it's hatched and empty. The only way to see them form a chrysalis for sure is to "trap" them and keep them in a container (make sure they have enough leaves to eat until they're ready to pupate). We just let our outdoor caterpillars do their thing instead, which means most of them "disappear" but we're pretty sure most turn into butterflies. Take another long look around your yard, and you might find a chrysalis. Good luck!

Comment by Alex on Sunday, December 11, 2016
Hello, One of my monarch caterpillars has fallen off of its leaf it was attached to. The branch was accidentally severed which wilted the leaf and when I was trying to move it to a safe place it detached and has not moved - it looks asleep, no movement. I have no experience with butterflies. Help pls, what can I do?

Reply by Steve (Cranial Borborygmus)
Hi Alex, When a Monarch caterpillar is disturbed (i.e. if they fall, or if you pick them up) I think they typically will curl up "play dead" for a while. Hopefully, that's all that was happening with your caterpillar, and after a while he should uncurl and crawl away. Good luck!

Comment by Eileen on Monday, January 23, 2017
I've had a similar problem with half-formed or less chrysalises in my last two cats. Both were brought in from the milkweed outside. The weather had been quite cold and windy here in FL, so we thought we were saving them. Both ate well and the second one was placed on a plant in a netted house. Yesterday I watered the plant in the cage and my cat fell down onto the wet ground. I tried to help it get back on a leaf and saw it crawl up a stem and stay there. This morning it hung straight down on that stem and its head had a small amount of chrysalis. It's obviously dead. Is handling the problem?

Reply by Steve (Cranial Borborygmus)
Hi Eileen, Thanks for your comment. I'm sorry to hear that the partial-pupation problem happened to two of your caterpillars. I don't know what causes it, but from the comments here, several people have seen it happen. A few theories have been posted here, but I don't know what actually causes it or if it could be multiple factors. I just know that it isn't very common, and I'm guessing that your next batch of caterpillars will do better. Good luck!

Comment by Joan Moore on Monday, May 29, 2017
Seems that I have had all of the same problems as the ones described above. It was ok trying to raise Monarchs in spring, but now in Ft. Lauderdale the temp has risen to 100 degrees with high humidity. One of my chrysalis fell from a leaf and the top popped off and an owey gooey yellow spilled out of the top. The one Monarch that was born in early May flies around and is constantly laying eggs. When they are not put into a cages the lizards eat them. Don't know how to stop the process and wait until it gets cooler in the fall. I get so upset when they get sick, just don't know what to do.

Reply by Steve (Cranial Borborygmus)
Hi Joan, Have you ever actually seen a lizard eat one of your caterpillars? We have a lot of "blue-belly" lizards around, especially this year, and I've sometimes wondered if they eat caterpillars, but I've never actually seen it happen. I like watching our lizards... I just hope they aren't eating our Monarch caterpillars!
I understand how depressing it can be to see the caterpillars and chrysalises not make it... but at least sometimes they do! I'm not sure what to recommend, other than it will be better in the fall. Good luck!

Comment by Joan Moore on Sunday, June 10, 2017
Thanks for getting back to me. I have never actually seen a lizard eat a caterpillar, but when I first started out with milkweed I moved my plant with at least 15 caterpillars from a very sunny place to a more shady area under a nice shrub. Also, I added a few other milkweed plants so they wouldn't run out of food. The pots were on the ground. At one point I walked over and saw two lizards fighting among the milkweed plants, although one was a curly tailed pot belly from the Bahamas, and very aggressive, I didn't think much of it until the next day every single caterpillar was gone from the tiniest to the full grown one a total of about 15 caterpillars. I was horrified and moved all of the plants out of the area. That was when I ordered the mesh cages. Only one Monarch caterpillar has survived out of 30 on its own. Now that I have the cage there are many chrysalis on the roof and I can't wait to see them hatch. The caterpillars also are now dining on cool cucumber chunks when they get big enough. Sometimes they lay across the cucumber, it is very cute. Happy Monarchs.

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