Something ate the leaves of my baby peppers

I have been growing some peppers from seed in my greenhouse. This week something just stripped the leaves on some of them. They were just getting their first true leaves. The only insect I saw was a yellow jacket bee on a new moon flower leaf. Could this be the killer?

I don't think yellow jackets would eat leaves--they'll get into fruits and things but I can't think of why they'd have any interest in leaves. Could it have been a leaf cutter bee rather than a yellow jacket? They will chew holes in leaves, but on a seedling those holes could be close to the size of the leaf so it could look like they ate most of the leaf. Leaf cutter bees are generally beneficial and on full-grown plants their damage is strictly cosmetic so I never really worry about them, but I guess on seedlings they might be more of a problem. The other possibility (which would have been my first guess if you hadn't mentioned the bee) is slugs/snails, I could picture a few of those finding their way into the greenhouse and munching stuff--have you seen any of them or their slime trails anywhere in the GH?