Black Swallowtail Caterpillars disappearing and dying

[Dollface]

I have a large planter pot on my patio that I transferred a bunch of parsley to in early August. 2 weeks ago I was watering plants and noticed 6, rather large and identifiable, black Swallowtail caterpillars on the parsley. I was immediately hit with joy and excitement.
I rushed to clean up the dying parsley, give them a nice home, made a mesh protective barrier to keep anything from bothering them and watched them grow more and more every day.

Well, this past Sunday I noticed we were missing 1, I thought maybe it got eaten by another due to some articles I read online about cannibalism as I searched for answers. I now think that was/ is not the case here. Yet, I still search for answers.

Yesterday, I awoke to find 2 of them not doing very well and barely moving. I put fresh parsley in to try to help them. Now, 1 is dead on the floor of the planter bed and the other is fighting for it's life, so it seems. It has it's little horns out constantly and is forever squirming around. I actually found it outside of the planter this morning, bathed it off with some water and put him on a safe, elevated piece of cardboard with parsley around him in hopes he will come back to good health. And then one of the 2 large, healthy ones are missing this morning, as well.

Do they leave to form their chrysalis elsewhere? I put vertical sticks in the planter in hopes that it would give them a place to continue their life cycle in the planter, away from any dangers.

Our weather has been terribly bad this past week and got unusually cold with nonstop rain that is supposed to continue. Could this be playing a part in their survival? It did seem strange to see them so late into the season.

I am new to this and trying desperately to learn as much as I can to ensure that they have happy, healthy little lives but I am not sure what to do at this point. There is 1 healthy, big guy left and 1 little baby that I recently found on our other parsley.
What happened?! Is there anything I can do to aid the ill one back to health? Is there anything I can do to ensure the 2 surviving ones will make it? Please help, any advice would be so greatly appreciated!

[applestar]

Some pictures of the remaining caterpillars so I can see how far along they are in development, and more details of how you are keeping them will help me to help you.

Black Swallowtails will make chrysalis for overwintering if the season is late, so that in itself should not matter.

If they have grown up to 5th instar, then they could have crawled away to make their chrysalis away from the food and their still voracious siblings, but if they are getting sick, then there could be other factors, too.

The one you found extending its horns in and out sounds like it was in pain or irritated, which could mean it had been infested by parasitic wasps or flies which may have happened while they were still out on their own, or your enclosure may have been infiltrated. They also might have ingested the parasite eggs that had been laid on their food plant/parsley. All could depend on the way you are trying to rise them. If it had diarrhea, then Bt infection and belly-ache is likely.

They should be kept as dry as possible and, when kept in enclosed habitat, their frass/poop should be removed daily, otherwise, they can get sick from fungal or bacterial infection.

[applestar]

This is an older thread from 2013 but may contain some related information
Subject: Black swallowtail caterpillar leaves plant and dies

If you are interested, we raised monarch butterfly caterpillars for years (and raised black Swallowtails as well alongside them). Here is one thread, and you can find more by perusing the Similar Topics list at the bottom of the page from there. The techniques and habitats we used are described in the threads.
Subject: 2015 Saving Monarch Butterflies By Raising Caterpillars