I've not seen slugs or snails skeletonize artichoke leaves like that leaving membrane. They just chomp away whole areas. More like caterpillar damage. There seems to be caterpillar faeces visible. Or is that my imagination?

The black specks?

Yes.

It looks like there are a few specks. I went out there and looked around under the leaves for any pests. The only thing I saw were ants. What should I do to identify what is causing the problem so I can take action before it's too late?

I would keep my eyes open, but that's not much damage. Probably some random nighttime feeder who moved on.

I hope your right Planatus. I am currently seeing the damage on two of four plants. I will be keeping my eyes peeled for more damage and will maybe sprinkle some garden dust around each one as a preventative measure.