Does that seedling in the middle have a piece of leaf lying on the ground?
If so, I would suspect a mouse more than a caterpillar. Just because of my experience with rabbits, they cut more than they eat a lot of times. Whereas with a caterpillar or slug you'll see holes and edges chewed off but not usually pieces of leaf on the ground.
Slugs, you can tell because they leave a slime trail as well.
Caterpillars, some brown or green poop on the leaf.
Also seems unusual to me that a caterpillar would go marauding from one seedling to another without finishing them off first. It seems more like an animal to me, but I could be wrong - I'm sure you folks have types of caterpillar that I've never seen so maybe they behave different.
