The caterpillar ate all the leaves on the buttonbush (Cephalanthus occidentalis) twig and is munching on the flowed bud. I found it on a buttonbush at the edge of the wetland behind the house and am rearing this caterpillar and keeping a good supply of fresh leaves for it to eat.
Wow, this is not only a stunning caterpillar but a stunning shot of it. Would love to see one, but need to be near the right larval food plants. Good luck rearing, it will be interesting to see photos of the moth (next year, I assume). V