A powerful pesticide, diatomaceous earth (or DE) controls ants, aphids, bedbugs, cockroaches, centipedes, earwigs, flea beetles, mites, scorpions, slugs, snails, and thrips. The way that diatomaceous earth kills insects is by absorbing the waxy layer on the surface of their skin, causing it to dry out. It also ruptures insect's cuticles, causing cell sap leakage. Best of all, unlike with other pesticides, the insects and other pests DE destroys never develop a resistance to it. Another of the most common diatomaceous earth uses is as a medium for many fungicides and herbicides.
To use diatomaceous earth as a pesticide, you can hide it under rocks, in wood piles and other spots to control pests in your yard, or you can blend it with water (1 cup DE per gallon of water) and spray a barrier of it around your house to keep pests out. Note that if you take this latter approach, the mixture will only work once it's dried and it may leave a visible white ring wherever applied.