That would be Mammillaria bombycina. Ive had insects chew up some of my most pokey cacti and succulents. its weird.

No doubt, Mammis and snails do not mix. Often times I will come out in the morning to check on stuff and snails are just crawling over the spines like it's no big deal. Try wrapping some thin copper/copper tape around the pots. Snails get shocked when they touch copper. Great deterrent but they can always still fall on from above.

Thanks Microthrix for the id. I would never have blamed the snail if I hadn't seen a snail climbing another cactus a month ago. After taking a picture I gave that snail the ceremonial quarterback throw. I never thought they could actually get between the thorns to eat the cactus.