Have you tried placing it on the leaves yourself? Sometimes they need a little direction.

You can't take a red-spotted purple off the leaf it was laid on. They make a string of frass from their original leaf, they rest on the end of it and go back and forth to eat at their leaf. Offering it food won't work, it needs its original leaf.

It's a good idea to do research on a particular caterpillar before trying to raise it. They each have their peculiarities.

Sherry