I'm curious too. I've been reading about food grade DE and plan on using it when I get laying hens next year in their dust bath. It is supposed to kill mites, could be useful in the bin if it doesn't harm the little fellas.

Diatomaceous Earth won't harm worms or warm blooded critters - it's commonly used in commercial scale worm bins

Bill

I started researching DE when I saw baby roaches in my worm bin which I keep in the crawl space under the house. Apparently the egg case was in some compost I put in the bin.

All references I could find saying it was safe for worms / used in commercial worm farms was the same quote from the manufacturer repeated on every web site selling DE. I did find University or government research saying to use DE to discourage earthworms.

The only DE I could find locally was "Greenlight" which contains attractants for some insects. I sprinkled some on top of the dry cardboard in the bin and on the ground around the bin and the roaches disappeared. I also had a serious mite issue at the time and they seemed to be greatly reduced also. The mite reduction may have been a coincidence since I was reducing feeding and moisture also.

I have since greatly increased feeding and moisture and have not seen a resurgence in mite population.

DE kills anything with a hard shell by cutting the shell with the sharp microscopic edges on the small grandules. It will not hurt soft bodied creatures. You can even eat the stuff yourself if it is foodgrade!

I was under the impression that putting too much lime in a bin would change the PH suddenly, that the worms will die. Should it be mixed with water and then sprayed on the bedding, or just sprinkle very, very sparingly in the bedding?
I consistently get a lot of mites in my bins, even though the bins aren't wet or over-fed.