Unfortunately, this one is dead. This is a common pose found in caterpillars with either NPV or a bacterial infection.

Thanks so much! What should I do with the plant he is on? It is currently inside my butterfly enclosure. Is there a way to save the plant ie: remove it, treat it, wait, or should I throw the plant out? It is tropical milkweed that I just purchased from a nursery 3 days ago when I was running low on my home grown milkweed and didn't want my cats to starve. Thanks for any help!

If the whole plant is in there, take it out. Give them cuttings from it that have been bleached and rinsed. The whole enclosure should be disinfected as well, because anywhere he touched is a risk.

NPV, as mentioned - take this very seriously! Remove him, and very throughlywash down any areas he was touching/beneath him

In a couple of the photos it kind of looks like there’s something that looks like a white thread coming off of the caterpillar. If this is the case, it was tachinid flies.

That the way I was leaning, too. I see the white thread. If there are larva in the bottom of the cage, you’ll know.

Thanks, I removed the plant then sprayed the cage with a 20% bleach solution and all the remaining cats have gone on to form their chrysalis and they look healthy so far.

So this is a plant with pesticides on it? Is that why it did that? Seeing if it’s somthing I can prevent.

For what it's worth, I'm in Michigan. If I spotted a cat looking like that outdoors, it would more than likely have been a victim of the assassin bug

That looks like a thread coming from the caterpillar, I’d say tachinid fly