I could see darkling beetles laying eggs in frass and surviving on the mixture of frass, dead bodies, and the occasional bit of salad delight offered to the roaches. I'm doubtful that they would actually harm the roaches unless you had massive quanitites of them... they aren't exactly speedy or overly voracious. I'm confident they can survive and breed with very little offered to them as well - I once tried to destroy a meaworm (Tenebrio molitor) colony by neglect. Didn't touch them, feed em, water them, or anything for about 18months and I still had adult beetles and larvae moving around. I feel like I almost created a perfect example of 'conservation of energy'...then I threw them in a big fire =P

If you really want a good clean-up crew for roaches, consider getting some Dermestid beetles; they'll take care of the dead and some shed skins for you. Springtails and isopods are fine for roaches too, although they obviously fare better with some kind of substrate, I really only use them for some collector species.


And on a side note as well - Lobsters kind of scare me at the rate at which they can breed, and the temperatures at which they can breed. They're kind of smelly too... I burn a lot of them if I can't feed them because no one seems to want them (the whole climbing thing, I suspect). If it weren't for the climbing and smell, they'd be the ultimate feeder insect to breed. You can't kill them with neglect either, they just keep breeding... Like you, I pretty much ignore my lobsters...and lats... thankfully down to small colonies now. I only keep the lobsters around because they're adorable.