Slugs ate my cactus! Really!

Well, maybe a little misleading, but technically, it's true:
They are cactus seedlings.

Those of us who have tried growing cactus species from seed like Escobaria, Echinocereus, Pediocactus, etc., know how vulnerable to drying out the tiny seedlings can be. So don't be surprised, thinking it would be too dry from slugs. Young cactus need constant moisture. And now that I have seen a slug in action, that's obviously good enough for it, even with a limestone topping of grit (about #1 size).

Most of these slaughtered seedlings already had at least a few of their first areoles with thorns, but that didn't seem to deter the devastation. Of course, the thorns would probably not be very stiff, being so young and tiny. Now that I know the culprit, I know this has happened in other years, as the resulting evidence is consistant:
often some remains of the tiny thornless (or almost thornless) balls can still be seen, and it looks like the top 3/4+ of the plants were surgically slice off.

Now when I say "that I have seen a slug in action", I have to relay in honesty that I did not actually see a slug eating a cactus. There is a slim possibility that I am wrong, but then tell me please: what would a slug be doing on top of limestone grit in a pot above ground? They are either attracted to lime, or to the succulent and vulnerable cactus balls. I would have though the former would be abhorrent to slugs, but I guess (by the evidence) that if the limestone is moist there is no detriment.

These tiny cactus seedlings seem to be beacons in the night for slugs. It's hard to know exactly when the slug(s) entered, but the pillaging began only a few days from complete removal of pots from bags. Prior to this, bags were opened intermittently, and then permanently.

Am I crazy here? I guess it wouldn't be the first time . . .

Always learning,
Rick

Oh what a shame!