When the birds poop after being treated for coccidiosis the parasite that caused it is then expelled from their body. When you throw food on the ground to chickens they eat all kinds gross things... poop being one of them. Therefore the worm enters back into the body of the chicken and it restarts. DE has always worked for me. It's not a waste of money, in my opinion, if it helps keep your birds healthy.DE is a waste of money. Worms cannot survive outside their host. When excreted, they are either dead or are dying.