Scott Strough wrote:No, DE run through a horse as a dewormer does NOT hurt Earthworms. Different kind of worm. You do need to use food grade though. That is important for both the horse and the earthworms. PS Earthworms actually eat DE and use it for grit in their digestive systems. Ironically they are attracted to it. Certainly doesn't harm them.
I agree with Scott. I use DE in my compost piles and the earth worms thrive just fine. I have several types including night crawlers and the red wigglers.
Btw, when using horse manure, make sure you let the compost pile sit for a week and cook before turning over. The horse does not thoroughly digest whole seed and the seed may germinate, thus creating unwanted weeds in a garden.