I was going to try earthworms. But I started to think of how easy it is for them to get access to bacteria. They burrow down into moist soil that is mixed in with their poop. Also I wouldn't know how to gut load them. I usually don't feed anything that can't be easily gut loaded.
I read something somewhere not sure but get a ten gallon tank, put sometop soil about 2 or 3 in. High, 3/4 the length of the tank, and gut lod by putting fresh veggies and stuff on the 1/4 that has about a inch or 2 of soil. I heard they will eat anything. But I don't know that's my 2 cents.