Well, if I'm not mistaken, supers live in tropical, forest floor type environment. So, there wouldn't really be an abundance of grain unless the natives go feed them! Sorry, don't mean to be sarcastic but an insect that lives in the soil, like nightcrawlers, supers, pill bugs, etc, usually lives on decaying plant matter.
Seems to me that if you want your critters to have a varied diet then you would want to introduce different types of feeders. IF all the feeders are all fed the same stuff then doesn't that sort of defeat the purpose? I understand that we want the feeders to be nourished but each is going to provide a source of different minerals and such.
So, the supers in my viv are eating. IF they weren't they wouldn't still be alive and multiplying after 3 years! Yes, they have been living in there for that long! They clean up the dead leaves and other plant litter and dead feeders that escape into the soil. When I clean house I remove feces and leave the rest for the supers. Now mind you my dragons don't get them often, only when once happens to surface when they are digging or when I lift the water tank or feeder dish. They are usually there on the surface just like red wigglers would be.
In my viv I have mealies, supers, red wigglers and other beneficial varmints growing in the soil. I think it's more natural and it cleans up the environment for my animals via a living soil.
Just my opinion.
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Marcia - FroggieB Dragons
www.froggieb.com/MHDHome.html