It looks like a Dahlia and looks (to me at least) like slug/snail damage rather than Caterpillars, but it could be any herbivore insect.

I think if it was caterpillars they'd have eaten more than that! Can you see any silvery snail trails, Aimankay? if not, it's something else. Try putting a few slug pellets around the plant and see if you catch anything. It could be tiny caterpillars, so give it a spray with systemic insecticide to be sure. The plant looks healthy enough, anyway. Annie

Thanks Kildermorie and Anneashby,

I have not seen any silver trail. I have put some pallets and didn't see any snail/ slug dead afterwards either. I have removed the affected leaves and will see if it happens again.