Diatomaceous Earth is one of the key ingredients to promoting a healthy, chemical free flock. It consists of fossilized remains of diatoms which were a type of hard-shelled algae. These microscopic fossils work by scratching and absorbing the waxy outer cuticle of insects (lice & mites) upon contact, causing death by desiccation. Hence, it should be generously applied to bedding, coop and run perches and nesting boxes and in especially in the dust bath box. Note: This powder is extremely fine and should only be distributed while wearing a face mask. Also remember that the DE must be food grade rated!
I also add Diatomaceous Earth to my feeder every morning. The manufacturer that I use recommends adding 2% DE to the feed. Studies have shown that DE in layer feed can also help to alleviate worms and other internal parasites. It has also been shown to increase egg production and shell strength as well. This is a no brainer for me at $14 for a 44lb. bag. For more information on this product or to read the study published by Poultry Science (2011)