This is a first for me. Over the last two days, four of my 4th and 5th instar caterpillars got off their host plant (rue) and were sitting on the bottom of the cage. I saw some pale green spots on the paper towels that line the cage. This was not the typical final purge, it was pale green and was probably a small drop that spread on the paper towel. The caterpillars were thrashing around and their osmeterium were out. The way they were thrashing around, it looked like they were in pain, if they can even feel pain like we do. Anyway, I felt something was seriously wrong so I euthanized them (freezer).

Has anyone had this happen/know what is wrong?

I am going to ask my neighbors if they sprayed anything recently, since my rue is on the fence line. I was so happy to find over 2 dozen new eggs over the past few days, and now I fear they're all going to die :(