I've been wondering about this as well. I started my chickens on non-medicated feed, have gone organic the whole time, but will worm them if I need to. From what I've been reading, DE will kill bugs that may be in the bedding or feed, but once it's wet it's not effective, so it doesn't seem like it would work well as a dewormer by feeding it to the chickens. I'm not sure about the organic wormers (Verm-X, etc.). $70 for 20 chickens for 6 months isn't outrageously expensive, but I'm not sure if it works and don't want to give it to my chickens if they don't need it. I just reread the section on worming in Storey's Guide to Raising Chickens, and the author recommends taking stool samples to the vet every 3 months or so for a year to monitor parasites in your chickens. She writes that healthy chickens in a reasonably sanitary environment should develop immunity to worms, and there's no point in routinely deworming chickens that don't need it. I'm not really sure what that means, if they have small levels of worms but not so much that it overwhelms them? I think that I'll take her advice about having the chickens' stools tested, just so I know what's going on with the worm situation.