Saving the laburnum. RIP Caterpillars

There's a small Cassia fistula growing in our garden, very slowly at that. It is less than six months old. It put out a bunch of new shoots last week. I went to inspect it yesterday, and to my astonishment and dismay, several stems were bare of leaf, chomped away.

 I mistook the caterpillar culprits for those of the common lime, and so gently moved them to the much bigger lime tree. They seemed to settle in well, and were wandering up the tree, and examining out leaves. However, google and the internet revealed that they were Lemon Emigrant caterpillars, which love Cassia! So what was I to do? Four leaf-chomping caterpillars and the little sarakonrai was not likely to survive, I thought.

No other suitable Cassia in the neighbourhood.

I wandered down to the lime tree in the evening. Three of the caterpillars were missing. I found one, curled up on a lime leaf. I moved it back to the sarakonrai hoping against hope that it would survive. It was gone this morning.

I do feel I panicked, and maybe the sapling would have still survived if I had let the caterpillars be? What if I had not examined the sapling yesterday?