Farmers dump an organic pesticide called diatomaceous earth, basically fossilized remains of marine phytoplankton over their grains to keep the bugs out. Diatomaceous earth kills bugs. Bugs with hard shells like fleas, ants, bed bugs, Japanese beetles and flea beetles. Slugs and snails don't like it either because when they slither and slink across it the DE acts like bits of shard glass. Shard cuts them up. Powderized eggshells work just like DE! And eggshells are organic and free.
Let me know if you've tried eggshells as an organic pest control or if you think you will in the future! I'm already pleased with the results.