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I have an organic garden, and use diatomaceous earth to discourage slugs from eating my plants. Lately I have worried that the diatomaceous earth might hurt the earthworms in my soil. Does diatomaceous earth have any detrimental effect on earthworms?

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It appears that earthworms will not be harmed by it. "Diatomaceous Earth will not harm warm-blooded animals or earthworms Earthworm farmers use it to treat their worm beds for parasites, fungus gnat larva etc. Earth worms are structurally different from insects in that they can actually digest particles of DE. The particles are then eliminated in their castings."

http://www.ghorganics.com/DiatomaceousEarth.html

Klendathu

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I'd add that the diatomaceous earth must be food grade for use in areas where there are worms - I couldn't find out why, except that pool grade diatomaceous earth will kill them.

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    Crystalline silica in the pool kind, which comes from salt water sources, is probably harder to digest than the amorphous silica in food grade diatomaceous earth, which comes from fresh water sources. I could be wrong about that being the reason. You can change amorphous silica into crystalline silica by heating it enough. Also, the pool kind is cancerous to humans, while the food grade kind is GRAS (generally regarded as safe). I imagine worms can get cancer. – Shule Apr 2 '15 at 2:15
  • I seriously doubt that pool grade DE is cancerous. I had pool for 15 years, and it had a DE filter. You add the DE to the filter by pouring into the skimmer, in other words, right into the water stream. I don't think that DE would be used in pool filters if it was cancerous. The only mentions that I've seen suggesting that pool grade DE is cancerous have been from people selling food grade DE. – Cary Jensen Apr 11 '15 at 22:45
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DE harms insects because it gets between pieces of their carapace and cuts them up and dries them out.

Worms are not insects and although a pile of dry DE might be rather excruciating to them, it won't harm them in the soil.

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