If they're outside, I let them do their thing and catch flies or spiders. If I'm growing them indoors, then I rehydrate freeze dried meal worms and use those. I have to cut them to make sure they fit. General rule of thumb is that whatever you're feeding them is only about 1/3 the size of the trap.
I'm not sure about potato bugs, but I don't see why those would be a problem.
Is there a significant nutritional difference between bloodworms and mealworms. I bought a bag of dehydrated mealworms today while picking up bird seed. I've been feeding my traps freeze dried bloodworms to supplement the VFTs outside. I know that spiders are the best food value for VFTs.
Once a month I soak the bloodworms in dilute Maxsea for an added boost. They seem to respond well to the treat! I've also got freeze dried crickets for my one Nep. but haven't fed it with them yet.