You need to decide exactly what is eating them before deciding to carry out any treatments. A photograph of the damage would be good, otherwise, are the holes in the centre of the leaves, circular parts cut out of the edge of the leaves, whole parts of leaves missing, soggy trails on any of them, any signs of visible infestation?

Also, go out at night with a flashlight, and see if you can catch it in the act, Manky: most leaf eaters work at night.