I know you'll think I'm crazy for saying this because monarch larva only eat milkweed, but I definitely saw some eating a vine in my yard. Monarch larva have a distinct look so cannot be mistaken.
This is the plant they were on:
The vine often has small 2-3 mm diameter burrs on it that stick to everything. It has big ugly seed pods in the fall. I think it had unimpressive white flowers in the spring.