First of all, make sure you wear gloves and a high quality dust mask/respirator when you handle it. While non toxic, it is abrasive to your hands AND your lungs. If you only have the cheapo dust masks, I'd think twice about using it - might be better to hold your breath. The cheapo felt ones don't make a good seal to your face. I use a good quality respirator.
I do not feed it to my chickens directly, but spread it around the coop, run, and nesting boxes to help control lice, mites and flies. I have not read anything convincing that it helps with intestinal worms, but on the other hand it is safe for them to eat so why not try it.
It is not effective if it gets wet.
I usually put on my gloves, respirator and safety glasses and sprinkle it around once a month in the summer when there are more flies and every few months in the winter. Like sprinkling powdered sugar on a cake
. I used to do a light sprinkling but this summer the flies were bad so I dumped about a few gallons in volume over a 100 square foot area and worked it in to the shavings in the coop and into the sand in my run. It helped a lot. Don't spread it around with the chickies around, especially if windy, let the stuff settle first. It is not good for them to breathe either.
I got a great tip once on BYC to reduce your exposure to it - put wood chips or whatever bedding / run material (I use sand) in a big plastic bin or box with lid, add some DE then shake the box/bin. Then put the bedding/run material in the coop, run or nesting box. This technique cuts down on the DE dust that would otherwise be blowing around when spreading it.
