|Sometimes dust baths aren't enough|
Worms can be a serious problem and DE is a great, cheap wormer. Worm medicine cannot target all kinds of worms, and you are not supposed to use more than one wormer at a time due to drug interactions. You can use DE at the same time you use a wormer though and increase your chances of killing the right worms. Worms can spread quickly and thankfully DE works quickly. One customer came in talking about a rooster that had several worms and she was worried about the worms spreading to all her other critters. DE solved that problem quickly. I told her to put DE in the feed and also rub it into the feathers (like a dust bath) and place it in the bedding. I could bore you to death with other examples.
DE also works on mites, fleas, and other nasty bugs. All you have to do is spread the DE on the floor, ground, bedding, whatever, or rub into fur, feathers, whatever, and you are good to go. It really is that simple. I cannot say enough good things about DE.