Warning: Eggshells Actually ATTRACT Slugs
A very popular gardening myth claims that coarsely crushed eggshells are very sharp and that slugs would tear their bodies open trying to cross them. Therefore, by surrounding a plant susceptible to slug damage with a ring of eggshells, you can protect it, because no slug would dare try to cross such a barrier.
In reality, however, the slugs are covered with “slime” (mucus) precisely to protect against cuts on rough surfaces. This slime is so efficient they can even cross shards of glass without any damage. Several studies have been made about slugs and eggshell barriers and the conclusion is clear: slugs will cross an eggshell barrier as if it weren’t there and without suffering any damage whatsoever.
Until recently, though, it was simply thought that eggshell barriers were not effective. But it’s worse then that. Eggshells, unless thoroughly rinsed, give off an odor that will actually attracts slugs! So “eggshell barriers” are not only ineffective, they actually make things worse.
Here is a website where you can see the damage: www.allaboutslugs.com/eggshell-myth-busted/.