There are silver trails left on the spines of the leaves after being stripped
The silvery trails are a sure sign of slugs or snails. Here is how to deal with them:
https://www.gardeningknowhow.com/plant-problems/pests/insects/kill-garden-slugs.htm
https://www.gardeningknowhow.com/plant-problems/insects/simple-slug-trap
https://www.gardeningknowhow.com/plant-problems/pests/insects/killing-slugs-with-beer.htm