kinda looks like slugs, although it could be small snails you'd be surprised how well they can climb. They mostly come out at night and are gone by morning, go check it out in the night with a light or first thing after sunrise. Easy fix if it is, get some bait, pet friendly works good, safer's and wilsons both make a product also scotts is good as well. Place bait in clumps around the plants and you'll find some deads ones if that's what's eating your plant. I think they like getting stoned and they don't go away once they've found the stash, but they like the bait better, then it dries them out to death, must be like crystal meth.