it sounds like slug damage to me they are active during the night..i'm not sure on your stance but if you want just sprinkle some slug pellets and see if any slugs are killed then that will give you the answer.
.there are numerous organic methods for slug control as well as pellets
.red lilly beetles will eat your lillies pick them off and squash them as you patrol during the day.
if you decide to use pellets on a regular basis i would suggest you start now as tahe winter has been so mild and the slugs are still active.you can also clear up any debris to stop them sheltering eg leaves,boards,old stones.plastic.
light fork or hoe you soil on a regular basis so birds can get at slug eggs.