To nancy1zak,
I use it too. I wouldn't put it in the run, because rain or dew will clump it or make it slimy & it won't go onto your chickens right... BUT, it also kills all the bugs in the run. Not what your chickens would want, certainly.
It has microscopic sharp points and it cuts insects & dries them out. I think it cuts the chitin as well as worms' skin (?)
Even if you have sand, not good to use outside except in a dust bath area.
It's plenty good on the floor of a coop to keep away breeding populations of mites & lice . It works on your chickens & in the food every few days or week --I just use a pinch-- to prevent internal parasites.
Be careful not to inhale much of it. Wear a dust mask while dusting your chickens, and don't hold them near your face for a couple days after.