I feed mine earthworms a lot. I would believe meal worms or superworms would be find to feed them... probably maggots as well, as long as your getting the clean sterile ones and not pulling them outta roadkill or something...
I feed maggot's to my fish they love em never tried chicken liver ,meal or super worm's though . They are ok from a bait shop although i won't buy blue one's just give them a rinse before you feed them .