Great question, and timely too! Diatomaceous Earth, often referred as “DE” is an off white talc-like powder that is the fossilized remains of marine phytoplankton. When sprinkled on a bug that has an exoskeleton (such as bed bugs, ants or fleas) it gets caught between their little exoskeleton joints. As they move, the diatomaceous earth acts like razor blades and cuts them up.
DE is almost pure silica (with some beneficial trace minerals); under a microscope, it looks like shards of glass (glass is made from silica). On any beetle-type insect that has a carapace, like fleas and cockroaches, the DE works under the shell and punctures the body, which then dehydrates and the insect dies. DE is nontoxic. There is no buildup of tolerance like there is to poisons because the method of killing is PHYSICAL, not chemical.
Lethal to fleas, it’s harmless to humans. In fact, farmers use “food-grade” DE in grain bins to keep bugs out of their grain.
If you have a flea problem stop by the Eagle Hardware and pick up some D.E.