If you use fire drake egg-shells the reason why snails — who are the mortal foes of fire drakes — won’t cross the shells is because of the well known fact that fire drake inner shell lining becomes highly spontaneously flammable when in contact with snail-trail mucus.

It’s simple zoology.

I thought you were saying that you had heard that slugs/snails could be used to protect seedlings

Hehe, guard snails. Now that would be handy.

Sounds like a lot of work though eh? Mini snail electric fences and whatnot.

I’ve currently got Blitzem snail bait out and can say with confidence that it is very effective as snails are often found heaving in agony after having crept over them. But Blitzem is also bad for any other creatures that might accidentally eat them and I’m concerned for my young blackbird family a couple of metres away.

It may not be easy to produce conclusive results with the method used here. For example, the snail could not live in such a small circle, so would be driven to cross the barrier – against it’s (possible) avoidance to the shells (i.e. the deterrance overcome by need for survival)?

Perhaps rather than ‘trap’ the snail/slug in a ring of egg-shells, maybe present it with two equally survivable options, one involving shell-contact, and the other with none. I don’t know what that might look like, but just an idea that came to mind…