Diatomaceous earth (DE) is a naturally occurring, fine powder made from the fossilized remains of tiny aquatic organisms called diatoms. It's commonly used as a non-toxic method to control external parasites like mites and lice in chickens. When sprinkled in chicken coops, nesting boxes, and dust bathing areas, DE works by physically damaging the exoskeletons of insects, leading to dehydration and death. While food-grade DE is considered safe for chickens, it's important to use it judiciously to avoid respiratory issues from excessive dust. It's worth noting that while DE becomes temporarily ineffective when wet, it regains its efficacy once it dries out.
Scanning electron micrograph of diatomaceous earth by Dawid Siodłak.