Beginner Gardening: What has happened to my asiatic lily?? UGH!, 1 by CapeCodGardener

CapeCodGardener wrote:
Something has either laid 1/2" clusters of dark brown eggs, or used my lilies (which have just finished blooming) as a latrine. Ugh. Snails, maybe? You can see evidence of chewing holes.

My beginner's question is: what has done this, and what can I do about it? I'm holding off on treatment because I don't want to harm something that might be possible be beneficial, though it's hard to believe something so ugly could be beneficial!

Thanks in advance.