The birds reveling in the backyard dust know what they are doing. Finely ground particles in such dust baths damage the exoskeletons of bothersome insects. Diatomaceous earth, a dust used to control caterpillars, works on the same principle. Composed of fossilized remains of single-celled plants called diatoms, a dust is formed by quarrying and processing these ancient deposits.
This material does not bother people and animals, but it destroys the protective outer layer or gut of many soft-bodied insects. Used primarily for garden pests, it will also help control aphids and ants in the lawn. If you plan to use diatomaceous earth to control pests, be sure to buy the type meant for horticultural use (not the type for use in swimming pool filters).