Leftwood said:It doesn't sound like it's one big chomp like a rabbit, so yes, I would guess slugs. Slugs are not insects so insect killers don't usually work well. I would use some slug bait made with iron phosphate. Like this:
Australis said:The lily in the second photo will be fine - its growth tip doesn't appear to be affected. The first will probably be okay, but the third certainly won't bloom.
It doesn't look like a critter has done the damage on the first two - far more likely to be a snail or slug. Are there any obvious snail or slug tracks nearby? They tend to leave a mucus-like residue at intervals along their path.