During this podcast Paul Wheaton and Jocelyn Campbell discuss Paul's diatomaceous earth article in detail. The number one reason to have it? It is a general insect control that you can eat. Anyone that eats grains. Eats it.
Diatomaceous Earth, or DE, is far more effective than any other pesticide because bugs can't build resistance to it. It works in two different ways. It is sharp for insects. It cuts and gets caught in the joints of their exoskeleton. It is a desiccant, meaning it dries things out. It turns bugs into little bug jerky.
Paul covers the variance in the grades of DE. There is a food grade version.
Diatomaceous Earth is the best stuff you can use on bed bugs, fleas, sugar ants, carpenter ants, flea beetles, and chicken mites. Add a little DE where the chickens take their dust bath. It is even used on slugs and pin worms.
It is often used for long term storage of legumes and grains.
Also, it is so useful on the homestead Paul calls it, "Duct tape for the homestead."